Pneumonia - InDepth






Risk Factors



Pharmacologic Intervention

Drug Classes




Inflammation in the Lungs

Pneumonia is inflammation of the air sacs in the lungs that is most often caused by infection with bacteria, viruses, or other organisms. Occasionally, inhaled chemicals other non-infectious factors can cause lung inflammation (pneumonitis). Age groups at the extremes, that is the very young and old, are more vulnerable to pneumonia. Healthy adults can usually fight off pneumonia caused by infections. However, it is easier for bacteria to grow in the lungs of people who are sick and have a weakened immune system, like those who are recovering from influenza (the flu) or an upper respiratory illness. Pneumonia is the 6th leading cause of death for Americans age 65 years and older. Worldwide, pneumonia (with a bacterial origin) is a leading cause of death in children under age 5 years.

Lung anatomy

When air is inhaled through the nose or mouth, it travels down the trachea to the left bronchus and right bronchus, where it first enters the lungs. From the bronchus, air goes through the smaller bronchi, into the even smaller bronchioles, and lastly into the alveoli.

Defining Pneumonia by Location in the Lung

Pneumonia may be defined according to its location in the lung:

Defining Pneumonia by Origin of Infection

Health care providers often classify pneumonia based on where the disease is contracted. This helps predict which organisms are most likely responsible for the illness and, therefore, which treatment is most likely to be effective.

Community-Acquired Pneumonia (CAP)

People with this type of pneumonia contracted the infection outside of a hospital setting. It is one of the most common infectious diseases. It often follows a viral respiratory infection, such as the flu.

One of the most common causes of bacterial CAP is Streptococcus pneumoniae. Other causes include Haemophilus influenza (H influenzae), Mycoplasma pneumoniae, and Chlamydia pneumoniae (not to be confused with a different chlamydia that is sexually transmitted).

Pneumonia Arising in Institutional Settings

The term "healthcare associated pneumonia" is also utilized for all the above types of pneumonia as a group.

Hospital-acquired pneumonia

Click the icon to see an image of hospital-acquired pneumonia.

Disease Process Leading to Pneumonia

Pneumonia-causing agents reach the lungs through different routes:

However, in normal situations, the airways protect the lungs from substances that can cause infection.

Blood cells

Click the icon to see an image of blood cells.

The above-mentioned defense systems normally keep the lungs healthy. If these defenses are weakened or damaged, however, bacteria, viruses, fungi, and parasites can easily infect the lungs, producing pneumonia.

The Lungs

The lungs are 2 spongy organs in the chest surrounded by a thin, moist membrane called the pleura. Each lung is composed of smooth, shiny lobes. The right lung has 3 lobes, and the left has 2. About 90% of the lung is filled with air. Only 10% is solid tissue. There are several parts to each lung.

When a person takes a breath (inhales), air travels from the windpipe (trachea) into the lung through the main (primary) right and left bronchi, which branch into smaller tubes called secondary bronchi.

The secondary bronchi keep dividing, like the branches of a tree, into smaller airways. The smallest tubes are called bronchioles.

The bronchioles lead to a group of microscopic sacs called alveoli, which look like clusters of grapes. Each healthy adult lung contains millions of tiny alveoli. (Note: The singular of alveoli is alveolus.)


Click the icon to see an image of the lungs.

Each alveolus has a thin membrane that allows oxygen and carbon dioxide to pass in and out of the capillaries, the smallest of the blood vessels, which surround the alveolus. When you take a deep breath, the membrane unfolds and expands. Fresh oxygen moves into the blood stream in the capillaries, and carbon dioxide passes from the capillaries into the air in the alveoli, where it is carried out of the body through the lungs.

Blood vessels carry the oxygen-rich blood to the heart, where it is pumped throughout the body.


Gram Staining

Bacteria are the most common causes of pneumonia. However, pneumonia can also be caused by viruses, fungi, and other agents. It is often impossible to identify the specific culprit.

Many bacteria are grouped into 1 of 2 large categories by a laboratory procedure known as Gram staining. Bacteria are stained with special dyes and then washed in a special solution. The color of the bacteria after washing determines whether they are Gram-negative or Gram-positive. Knowing which group the bacteria belong to helps determine the severity of the disease, and how to treat it. Different bacteria are treated with different drugs.

Gram-Positive Bacteria

These bacteria appear blue on the stain and are the most common organisms that cause pneumonia. They include:

Gram-Negative Bacteria

These bacteria stain pink. Gram-negative bacteria commonly cause infections in hospitalized or nursing home patients, patients with cystic fibrosis, and people with long-term (chronic) lung conditions.

Atypical Pneumonia

Atypical pneumonia generally produces milder symptoms and a dry cough. They are called atypical because they produce symptoms besides those related to the lung, may appear different on chest x-ray, and respond to different antibiotics than "typical" pneumonias. "Mini-epidemics" are sometimes seen in school or military settings. It occurs at any age, but it is more common in children and young adults. Organisms that cause atypical pneumonia include:

Legionnaire disease - organism legionella

Legionnaires disease was first described in 1976 after an outbreak of fatal pneumonia at an American Legion convention. The organism that caused the disease was named Legionella pneumophila, shown in this picture. (Courtesy of the Centers for Disease Control and Prevention.)

Viral Pneumonia

Viral pneumonia accounts for a third or more of CAP cases. In young children, viral pathogens cause the majority of CAP cases. Many viruses can cause pneumonia, either directly or indirectly. They include:

Avian Influenza Pneumonia

"Bird flu" (type A influenza subtype H5N1) is spreading around the globe. Fortunately, only a few hundred human cases have been identified. Most have resulted from close contact with infected birds. The virus does not seem to spread easily from person to person. All people diagnosed with "bird flu" show signs of pneumonia, although symptoms may be mild. Oseltamivir (Tamiflu) is the most effective treatment for this type of influenza, which can be fatal.

A newer strain of avian influenza, H7N9, has been reported in humans in China as of 2013. This new "bird flu" strain causes severe pneumonia and has a high mortality rate, though to date the virus is not transmitted from human to human.

Middle East respiratory syndrome coronavirus (MERS-CoV)

A new cause of severe pneumonia was first reported in Saudi Arabia in September 2012. Within a year, 58 cases, including 33 deaths, were reported in Jordan, Qatar, Saudi Arabia, the United Arab Emirates (UAE), France, Germany, Italy, Tunisia, and the United Kingdom. Since 2012 there have been over 1730 cases. The World Health Organization warns this new viral illness could become a pandemic. However, person-to-person transmission has been limited to close contacts. In the United States, no cases of MERS have been reported since 2014.


Coronavirus disease 2019 (COVID-19) is a respiratory illness caused by the SARS-CoV-2 virus (severe acute respiratory syndrome coronavirus 2). SARS-CoV-2 is a betacoronavirus, like the MERS and SARS coronaviruses. COVID-19 was first reported in Wuhan City, Hubei Province, China in early December 2019. Since then, it quickly spread within China and to other locations on all continents, causing a pandemic.

COVID-19 is thought to spread to people within close contact (about 6 feet or 1.8 meters). When someone with the illness coughs or sneezes, infected droplets spray into the air. You can catch the illness if you breathe in droplets, or if you touch these particles and then touch your face. It is more infectious than the flu and other epidemic coronaviruses (SARS and MERS) and this led to the current pandemic.

COVID-19 can cause mild to serious illness. Severe COVID-19 can lead to pneumonia and even death. The United States Centers for Disease Control and Prevention (CDC) and the World Health Organization consider COVID-19 a serious public health threat globally and in the United States. The situation is evolving quickly, so it's important to follow current local guidance on how to protect yourself and others from getting and spreading COVID-19.

Aspiration Pneumonia and Anaerobic Bacteria

The mouth contains a mixture of bacteria that is normally harmless. However, if this mixture reaches the lungs, it can cause a serious condition called aspiration pneumonia. This may happen after a head injury or general anesthesia, or when a person takes drugs or alcohol. In such cases, the gag reflex does not work as well as it should, so bacteria can enter the airways. Unlike other organisms that are inhaled, some of the bacteria that cause aspiration pneumonia do not need oxygen to live. These bacteria are called anaerobic bacteria.

Opportunistic Pneumonia

Impaired immunity leaves people vulnerable to serious, life-threatening pneumonias known as opportunistic pneumonia. They are caused by organisms that are harmless to people with healthy immune systems. Such organisms include:

In addition to AIDS, other conditions put people at risk for opportunistic pneumonia. They include cancers, such as lymphoma and leukemia. Long-term use of corticosteroids and drugs known as immunosuppressants also increases the risk for these pneumonias.


Mycobacterium tuberculosis is the microorganism responsible for causing tuberculosis (TB), a long-term (chronic) granulomatous disease primarily involving the lung. Although not common in the United States, TB affects almost a quarter of the world population and is one of the top 10 causes of mortality globally. TB is usually a chronic lung condition, but can sometimes manifest as pneumonia, particularly in immunocompromised people, and must be distinguished from it in the diagnosis process.

Occupational and Regional Pneumonias

Exposure to chemicals can also cause inflammation and pneumonia. Where you work and live can put you at higher risk for exposure to pneumonia-causing organisms.

Inhalation Anthrax

Click the icon to see an image of inhalation anthrax.

Inhalation or respiratory anthrax is a life-threatening infectious disease caused by inhaling the spores of the bacterium Bacillus anthracis. Although the spores are dormant when breathed in, they germinate when exposed to a warm, moist environment, such as the lungs. Not all particles are small enough to pass into the alveoli, or air sacs, but those that do begin to multiply and may spread to the lymphatic system. When the spores germinate, several toxins are released. Particles illustrated are not to scale.

Coccidioidomycosis - chest X-ray

Click the icon to see an image of an x-ray of coccidioidomycosis.
Hanta virus

Click the icon to see an image of hanta virus.


General Symptoms

Symptoms vary among children, adults, and older people. The symptoms of some bacterial pneumonias, such as pneumococcal pneumonia, develop very quickly and typically include:

Emergency Symptoms

Symptoms of pneumonia indicating a medical emergency include:

Symptoms in Children

Common symptoms in infants include fever, rapid breathing, nasal flaring, and low oxygen saturation. Children ages 2 to 4 years with pneumonia usually present with a cough plus one or more lower respiratory tract infection symptoms, such as fever, rapid breathing, and low oxygen levels.

Symptoms in the Elderly

It is important to note that older people may have fewer or different symptoms than younger people. Symptoms may be subtle or non-specific. Some older people may be confused, lethargic, and show general deterioration.

Symptoms of Atypical Pneumonia

Atypical pneumonia is most commonly caused by mycoplasma, chlamydia, or a virus. It usually appears in children and young adults. Symptoms are usually mild and often go undiagnosed and untreated. Legionnaire disease, however, is a severe form of atypical pneumonia that usually strikes adults and seniors.

The disease progresses gradually:



Between 5 and 10 million people get pneumonia in the United States each year. More than 1 million people are hospitalized due to the condition. In 2015, pneumonia was the 5th most common cause of hospitalization in the US.

Although the majority of people with pneumonia respond well to treatment, the infection kills 40,000 to 70,000 people each year. In 2020, SARS-CoV-2 infection has dramatically increased these numbers.

Men with CAP tend to fare worse than women.

Outlook for High-Risk Individuals

Hospitalized Patients

The death rate for CAP can range from well below 5% in mildly ill outpatients to 10% to 30% in seriously ill patients who need to be admitted to a hospital. If pneumonia develops in patients already hospitalized for other conditions, or those in a nursing home, death rates can be much higher. This is true for anyone who is on a ventilator.

Older Adults

CAP is responsible for 350,000 to 620,000 hospitalizations in older people every year. Older adults have lower survival rates than younger people. Even when older individuals recover from CAP, they have higher-than-normal death rates over the next several years. Older people who live in nursing homes or who are already sick are at particular risk.

Very Young Children

Small children who develop pneumonia and survive are at risk for developing lung problems in adulthood, including chronic obstructive pulmonary disease (COPD). People with a history of pneumonia and other respiratory illnesses in childhood are more than twice as likely to die of COPD as those without a history of childhood respiratory disease.

Pregnant Women

Pneumonia poses a special hazard for pregnant women, possibly due to changes in a pregnant woman's immune system. This complication can lead to premature labor and increases the risk of death during pregnancy.

Patients With an Impaired Immune System

Pneumonia is particularly serious in people with an impaired immune system. This is particularly true for AIDS patients.

Patients With Serious Medical Conditions

Pneumonia is also very dangerous in people with diabetes, cirrhosis, sickle cell disease, cancer, and in those whose spleen has been removed.

Risk by Organisms

Specific organisms vary in their effects. Mild pneumonia is usually associated with the atypical organisms mycoplasma and chlamydia. Severe pneumonia is most often associated with a wide range of organisms. Some are very potent (virulent) but extremely curable, while others are difficult to treat:

Complications of Pneumonia


An abscess in the lung is a thick-walled, pus-filled cavity that forms when infection has destroyed lung tissue. It is more commonly seen with aspiration pneumonia, when a mixture of organisms is carried into the lung. Untreated abscesses can cause hemorrhage (bleeding) in the lung, but targeted antibiotic therapy significantly reduces the danger. Drainage with a needle may also be needed. Abscesses are more common with anaerobic bacteria, S aureus, P aeruginosa, or K pneumoniae, and are uncommon with S pneumoniae.

Respiratory Failure

Respiratory failure is one of the top causes of death in people with more severe pneumonia. Acute respiratory distress syndrome (ARDS) is the specific condition that occurs when the lungs are unable to function and oxygen is so severely reduced that the person's life is at risk. Failure can occur if pneumonia leads to physical changes in the lungs that make it even harder for the lungs to exchange oxygen (ventilatory failure).


Bacteremia -- bacteria in the blood -- is the most common complication of pneumococcus infection, although it rarely spreads to other sites. Bacteremia is a frequent complication of infection from Gram-negative organisms, including H influenzae.

Pleural Effusions and Empyema

The pleura is a 2-layered membrane that surrounds each lung. In some cases of pneumonia the pleura becomes inflamed, which can result in breathlessness and chest pain when breathing.

In about 20% of pneumonia cases, fluid builds up between the pleural membranes, a condition known as pleural effusion. Ordinarily, the narrow zone between the 2 membranes contains only a tiny amount of fluid, which lubricates the lungs.

In most cases, particularly in S pneumoniae, the fluid remains sterile (no bacteria are present), but occasionally it can become infected and even filled with pus, a condition called empyema. Empyema is more likely to occur with specific organisms, such as S aureus or K pneumoniae infections. The condition can cause permanent scarring.

Collapsed Lung

In some cases, air may fill up the area between the pleural membranes, causing the lungs to collapse. This is called pneumothorax. It may be a complication of pneumonia (particularly S pneumoniae) or of the invasive procedures used to treat pleural effusion.

Pneumothorax - chest X-ray

Pneumothorax occurs when air leaks from inside the lung to the space between the lung and the chest wall. The lung then collapses. The dark side of the chest (right side of the picture) fills with air from outside of the lung tissue.

Other Complications of Pneumonia

In rare cases, infection may spread from the lungs to the heart and possibly throughout the body. This can cause abscesses in the brain and other organs. Bacterial pneumonia is linked with an increased risk of acute heart problems, such as heart attack or abnormal heart rhythm (arrhythmia).

Kidney complications and electrolyte imbalances are common in people admitted to the hospital with pneumonia. If not treated, these problems cause more severe illness and increase the risk of death. Hydration through a vein (intravenous) controls the problem.

Long-Term Effects of Atypical Pneumonias

Pneumonias caused by the atypical organisms mycoplasma and chlamydia are usually mild.


Chlamydia pneumoniae, Mycoplasma pneumoniae, and RSV are becoming suspects in many cases of severe adult asthma.

Risk Factors

Risk Factors for Hospital-Acquired Pneumonia

Pneumonia that is contracted in the hospital is called hospital-acquired, or nosocomial, pneumonia. It is the most common hospital-acquired infection in the intensive care unit (ICU). It affects an estimated 5 to 10 of every 1,000 hospitalized patients every year. More than half of these cases may be due to strains of bacteria that have developed resistance to antibiotics. In fact, methicillin-resistant Staphylococcus aureus (MRSA) and multidrug-resistant P aeruginosa are leading causes of death from hospital-acquired pneumonia. Those at highest risk are:

Hospitalized patients are particularly vulnerable to Gram-negative bacteria and staphylococci, which can be particularly dangerous in people who are already ill.

Risk Factors for Community-Acquired Pneumonia

CAP is the most common type of pneumonia. It develops outside of the hospital. Each year 2 to 4 million people in the US develop CAP, and 600,000 are hospitalized. Older people, infants, and young children are at greatest risk for the disease.

Chronic Lung Disease

Chronic obstructive lung disease (COPD), which includes long-term (chronic) bronchitis and emphysema, affects 15 million people in the US. This condition is a major risk factor for pneumonia. Long-term use of corticosteroid inhalers may increase the risk of pneumonia in people with COPD. People with other types of chronic lung diseases, such as bronchiectasis and interstitial lung diseases, are also at increased risk for getting pneumonia and more likely to have complications.


Bronchitis is the inflammation of the bronchi, the main air passages to the lungs. It generally follows a viral respiratory infection. Symptoms include coughing, shortness of breath, wheezing, and fatigue.


Click the icon to see an image of emphysema.

People With Compromised Immune Systems

People with impaired immune systems are extremely susceptible to pneumonia. It is a common problem in people with HIV and AIDS. A wide variety of organisms, including P jiroveci, Myobacterium species, Histoplasma capsulatum, Coccidioides immitis, Aspergillus species, cytomegalovirus, and Toxoplasma gondii, can cause pneumonia.

In addition to AIDS, other conditions that compromise the immune system include:

People who are on corticosteroids or other medications that suppress the immune system (such as chemotherapy drugs) are also prone to infection.

Also, drugs that treat gastroesophageal reflux (GERD) may slightly increase one's risk for CAP. People at high risk for pneumonia should take gastric acid-suppressing drugs only when necessary and at the lowest possible dose. This association is strongest with protein pump inhibitors (PPIs). Reducing levels of bacteria-killing stomach acid may allow germs to spread in the upper gastrointestinal tract and move into the respiratory tract. The risk posed by these medications is highest in:

The risk is strongest when people have recently begun treatment with PPIs, and lessens over time.

Swallowing disorders, including dysphagia

Difficulty swallowing has a variety of causes, including:

All of these may increase the risk of aspiration pneumonia.


Click the icon to see an animation about heartburn.

Factors Associated with a Higher Risk in Healthy Adults

Dormitory or Barrack Conditions

Recruits on military bases and college students living in dormitories are at higher-than-average risk for Mycoplasma pneumonia. These groups are at lower risk, however, for more serious types of pneumonia.

Smoke and Environmental Pollutants

The risk for pneumonia in people who smoke more than a pack a day is 3 times that of nonsmokers. Those who are chronically exposed to secondhand cigarette smoke, which can injure airways and damage the cilia, are also at risk. Quitting smoking reduces the risk of dying from pneumonia to normal, but the full benefit takes up to 10 years to be realized. Toxic fumes, industrial smoke, and other air pollutants may also damage cilia function, which is a defense against bacteria in the lungs.

Drug and Alcohol Abuse

Alcohol or drug abuse is strongly associated with pneumonia. These substances act as sedatives and can diminish the reflexes that trigger coughing and sneezing. Alcohol also interferes with the actions of macrophages, the white blood cells that destroy bacteria and other microbes. Intravenous drug abusers are at risk for pneumonia from infections that start at the injection site and spread through the bloodstream to the lungs.


Men with CAP tend to fare worse than women. Men are 30% more likely than women to die from the condition.

Specific Risk Factors for Recurrent Pneumonia in Children

Certain children have a higher-than-normal risk for pneumonia and pneumonia that returns. Conditions that predispose infants and small children to pneumonia include:


Diagnostic Challenges

Diagnostic Difficulties in CAP

It is important to determine whether the cause of CAP is a bacterium, atypical bacterium, or virus, because they require different treatments. In children, for example, S pneumoniae is the most common cause of pneumonia, but RSV may also cause the disease. Although symptoms may differ, they often overlap, which can make it difficult to identify the organism by symptoms alone. The cause of CAP is found in only about half of cases.

Nevertheless, in many cases of mild-to-moderate CAP, the physician is able to diagnose and treat pneumonia based solely on a medical history and physical examination.

Diagnostic Difficulties with Hospital-Acquired (Nosocomial) Pneumonia

Diagnosing pneumonia is particularly difficult in hospitalized patients for a number of reasons:

Medical and Personal History

The person's history is an important part of making a pneumonia diagnosis. People should report any of the following:

Physical Examination

Auscultation (Use of the Stethoscope) and Percussion

The stethoscope is the tool that the physician uses to listen to the body sounds, including chest sounds produced while breathing. Sounds that may indicate pneumonia include:

Pulse Oximetry

A pulse oximetry test can help determine if a person needs hospital care. A simple test using a device on the fingertip or earlobe, determines the amount of oxygen in the blood.

Laboratory Tests

Although current antibiotics can attack a wide spectrum of organisms, it is best to use an antibiotic that targets the specific one making a person sick. Unfortunately, people carry many bacteria, and sputum and blood tests are not always effective in distinguishing between harmless and harmful kinds. The Infectious Diseases Society of America/American Thoracic Society (IDSA/ATS) recommends diagnostic testing when it may impact the choice of antibiotic and in people with a high likelihood of accurate results (sicker patients). Many of these laboratory tests take 4 to 5 days or longer to complete, however, and therapy should be started before results are available.

Although viral pneumonia accounts for more than a third of CAP cases, it can sometimes be difficult to determine if the pneumonia is viral or bacterial in origin.

In severe cases, a doctor needs to use invasive diagnostic measures to identify the cause of the infection. These tests are not commonly performed in outpatients. Standard lab tests are used to help diagnose pneumonia.

Sputum Tests

A sputum sample may reveal the organism causing the infection.

The person coughs as deeply as possible to bring up mucus from the lungs, since a shallow cough produces a sample that usually only contains normal mouth bacteria. Some people may need to inhale a saline spray to produce an adequate sample. In some cases, a tube will be inserted through the nose into the lower respiratory tract to trigger a deeper cough.

The physician will check the sputum for:

The sputum sample is sent to the laboratory, where it is analyzed for the presence of bacteria and to determine whether the bacteria are Gram-negative or Gram-positive.

Blood Tests

The following blood tests may be performed:

Urine Tests

Urine antigen tests for Legionella pneumophila (Legionnaires disease) and S pneumoniae may be helpful in some people with severe CAP.

Invasive Tests

In critically-ill people with VAP, doctors have tried sampling fluid taken from the lungs or trachea. These techniques enabled the physicians to identify the pneumonia-causing bacteria and start the appropriate antibiotics. However, this made no difference in the length of stay in the ICU or hospital, and there was no significant difference in outcome.

Imaging Techniques


A chest x-ray is nearly always taken on a patient admitted to the hospital to confirm a pneumonia diagnosis.


X-rays are a form of electromagnetic radiation (like light). They are of higher energy, however, and can penetrate the body to form an image on film. Structures that are dense (such as bone) will appear white, air will be black, and other structures will be shades of gray depending on density. X-rays can provide information about obstructions, tumors, and other diseases, particularly when coupled with the use of barium and air contrast within the bowel.

A chest x-ray may reveal the following:

Other Imaging Tests

Computed tomography (CT) scans or magnetic resonance imaging (MRI) scans may be useful in some circumstances, such as when:

CT scan

Click the icon to see an image of a CT scan.

CT and MRI can help detect tissue damage, abscesses, and enlarged lymph nodes. They can also detect some tumors that block bronchial tubes. No imaging technique can determine the actual organism causing the infection. However, features on the CT scan of people with certain forms of pneumonia -- for example that are caused by Legionella pneumophila -- are usually different from features produced by other bacteria in the lungs.

Invasive Diagnostic Procedures

Invasive diagnostic procedures may be necessary when:


If a doctor detects pleural effusion during the physical exam or from an imaging procedure, and suspects that pus (empyema) is present, a thoracentesis is performed.

Complications of this procedure are rare, but they can include collapsed lung, bleeding, and infection.


Bronchoscopy is an invasive test to examine respiratory secretions. It is not usually needed in people with CAP, but it may be appropriate for people with a severely compromised immune system who need immediate diagnosis, or in people whose condition has worsened during treatment. In patients who need a breathing machine to breathe (severely ill) this procedure can be done via the existing breathing tube.

A bronchoscopy is done in the following way:


Click the icon to see an image of a bronchoscopy.

Bronchoalveolar lavage (BAL) may be done at the same time as bronchoscopy. This involves injecting high amounts of saline through the bronchoscope into the lung and then immediately sucking the fluid out. The fluid is then analyzed in the laboratory. BAL is an effective method for detecting specific infection-causing organisms.

The procedure is usually very safe, but complications can occur. They include:

Lung Biopsy

In very severe cases of pneumonia or when the diagnosis is unclear, particularly in people with a damaged immune system, a lung biopsy may be required. A lung biopsy involves taking some tissue from the lungs and examining it under a microscope.

Lung Tap

This procedure typically uses a needle inserted between the ribs to draw fluid out of the lung for analysis. It is known by a number of names, including:

This is a very old procedure that is not done often anymore because it is invasive and poses a slight risk for collapsed lung. Some experts argue, however, that a lung tap is more accurate than other methods for identifying bacteria, and the risk it poses is slight. Given the increase in resistant bacteria, they believe its use should be reconsidered in young people.

An infectious disease specialist may need to be consulted in severe or difficult cases.

Differential Diagnosis

Common Causes of Persistent Coughing

The four most common causes of persistent coughing are:

Other common causes of long-term (chronic) cough include heavy smoking or the use of blood pressure drugs known as ACE inhibitors.

Acute Bronchitis

Acute bronchitis is an infection in the passages that carry air from the throat to the lung. The infection causes a cough that produces phlegm. Acute bronchitis is almost always caused by a virus and usually clears up on its own within a few days. In some cases, acute bronchitis caused by a cold can last for several weeks.

Chronic Bronchitis

Chronic bronchitis causes shortness of breath and is often accompanied by infection, mucus production, and coughing, but it is a long-term and irreversible condition. The same bacteria and viruses that cause pneumonia can cause an infection in people with chronic bronchitis. However, infections involve only the airways leading to the lungs, and not the lung tissue itself. The 2 disorders may share the same symptoms, such as:

There are significant differences between chronic bronchitis and pneumonia:


In asthma, the cough is usually accompanied by wheezing and occurs mostly at night or during activity. Fever is rarely present (unless the person also has an infection). Asthma symptoms from occupational causes can lead to persistent coughing, which is usually worse during the workweek. Tests, like the methacholine inhalation challenge and pulmonary function studies, may be effective in diagnosing asthma. Chest X-ray can also help in ruling out pneumonia.

Other Disorders that Affect the Lung

Many conditions mimic pneumonia, particularly in hospitalized patients. They include:

Ruling Out Causes in Children

Important causes of coughing in children at different ages include:



The approach to treating people with pneumonia generally involves:

Whether people are treated at home or admitted to the hospital, receiving their first dose of antibiotics quickly improves the outcome of the illness and the speed at which they get better.

Determining the Need for Hospitalization

Determining the site of care is an important clinical decision. A clinician must decide whether the person would best be treated in one of the following settings:

Many adult people do not need to be hospitalized for pneumonia, and can be safely treated at home. Likewise, many people who are admitted to the hospital could be released sooner. Strategies are being devised to determine which people can be safely discharged and when they can be discharged. In general, low-risk people with mild-to-moderate pneumonia do just as well when treated as outpatients. They return to work and normal activities faster than those treated in the hospital.

A variety of guidelines and tools have been developed to help determine who can safely be treated at home and who cannot. Commonly used tools include the Pneumonia Severity Index (PSI), British Thoracic Society Rule (BSR), and CURB-65. All of these assessment tools evaluate several risk factors. The more of these risk factors that are present, the less likely  it is that the person can be safely treated at home. The combination of these risk factors determines a specific score or risk group, helping to guide the clinician in the decision. The results must be used along with the doctor's clinical judgment.

Some of the important factors used to make a decision include:


Other Medical Illnesses

People may be considered at greater risk if they have:

Findings on a Physical Exam

Concerning findings include:

Laboratory and X-ray Findings

Laboratory findings that are of concern include:

People with very few of these risks often can be discharged with outpatient care only. This determination can often be made with a simple physical examination and history. Sometimes a person needs to be hospitalized for only 24 hours for observation.

People with higher scores on these assessment tests often have many risk factors and usually are hospitalized.

When possible, treatment of CAP should be started within 4 hours of admission to the emergency room or hospital to reduce the chances of mortality and decrease the amount of time a person needs to spend in the hospital.

The following characteristics should prompt hospitalization in children and infants:

Home care may be possible, even in severe cases, when there is good support and available home nursing services. Often, caregivers can even be trained to administer intravenous antibiotics and chest therapy to people at home.

Home Treatment

The following tips are suggested:

Hospitalization Guidelines


If the pneumonia is severe enough for hospitalization, the standard treatment is intravenous antibiotics for 5 to 8 days. In cases of uncomplicated pneumonia, many patients may need only 2 or 3 days of intravenous antibiotics followed by oral therapy. Antibiotics taken by mouth are prescribed when the patient has improved substantially or leaves the hospital.

IDSA/ATS guidelines recommend that patients admitted to the hospital (but not the ICU) be treated with fluoroquinolones or a beta-lactam (such as cefotaxime [Claforan] or ceftriaxone [Rocephin]) plus a macrolide.

Duration of Stay

Patients should remain in the hospital until all their vital signs are stable. Most patients become stabilized in 3 days and can continue treatment at home. Many experts use these 7 variables to measure stability and to determine whether the patient can go home:

  1. Temperature

    Some experts believe that patients can go home when their temperature drops to 101°F (38.3°C). Stricter criteria require that it be at or close to 98.6°F (37°C).

  2. Respiration rate

    The goal is a normal breathing rate, although expert opinion differs on the degree of normality required for discharge.

  3. Heart rate

    The goal is 100 beats per minute or less.

  4. Blood pressure

    The goal is systolic blood pressure of 90 mm Hg or greater.

  5. Oxygenation

    The doctor determines the goal.

  6. The ability to eat

    The goal is regular appetite.

  7. Mental function

    The goal is normal.

Patients or their families should discuss these criteria with their doctor.

Chest Therapy

Chest therapy using incentive spirometry, rhythmic inhalation and coughing, and chest tapping are all important techniques to loosen the mucus and move it out of the lungs. It should be used both in the hospital and during recovery at home.

Incentive Spirometry

The person uses an incentive spirometer at regular intervals to improve breathing and loosen sputum. The spirometer is a hand-held clear plastic device that includes a breathing tube and a container with a movable gauge. The person exhales, then inhales forcefully through the tube, using the pressure of the inhalation to raise the gauge to the highest level possible.

Rhythmic Breathing and Coughing

During recovery, the person performs rhythmic breathing and coughing every 4 hours:

Oxygen Therapy

People who are not able to get enough oxygen into their cells and bloodstream may need oxygen therapy. It may be done in the hospital or at home under medical supervision. Delivery systems include an oxygen concentrator or more mobile cylinder option. Nasal prongs or a face mask will deliver the oxygen. Oxygen levels will be monitored regularly. Anyone using oxygen should stay away from open flames, including cigarettes.

Pharmacologic Intervention

Choosing the Right Antibiotic

Dozens of antibiotics are available for treating pneumonia, but selecting the best drug is sometimes difficult. People with pneumonia need an antibiotic that is effective against the organism causing the disease. When the organism is unknown, "empiric therapy" is given, meaning the doctor chooses which antibiotic is likely to work based on factors such as the person's age, health, and severity of the illness.

In adults, the choice of antibiotic therapy depends on the severity of infection and site of care. In all cases, the more quickly antibiotic therapy is started once the diagnosis is made, the better the outcomes. In most cases, the organism causing the pneumonia will not be known before antibiotic therapy is started, so the doctor must choose an antibiotic regimen based on history and symptoms. Later, the therapy may be altered when more information becomes available. To determine the appropriate antibiotic, the doctor must first answer a number of questions:

Once an antibiotic has been chosen, there are still difficulties:

Antibiotic Treatments for Community-Acquired Pneumonia

For a more detailed discussion of the different types of antibiotics, see the "Antibiotic Classes" section below.

Joint guidelines issued in 2019 by the IDSA/ATS recommend that mild CAP in otherwise healthy people be treated with amoxicillin or doxycycline. If the person lives in an area with low S pneumoniae resistance to macrolides, a macrolide antibiotic therapy (such as azithromycin or clarithromycin) may also be considered.

The British Thoracic Society recommends amoxicillin, doxycycline, or clarithromycin as alternatives.

Many people with heart disease, kidney disease, diabetes, or other coexisting conditions may still be treated as outpatients.

People with coexisting conditions should be given a macrolide plus a beta-lactam (amoxicillin/clavulanate or a cephalosporin) or a fluoroquinolone as monotherapy. Doxycycline can be given as an alternative to a macrolide. Current recommendations call for at least 5 days of antibiotic therapy. People should have no fever for at least 48 hours and no more than one sign of continuing severe illness before discontinuing antibiotics.

Many cases of CAP are caused by S pneumoniae -- Gram-positive bacteria that usually respond to antibiotics known as beta-lactams (which include penicillin), and to macrolides. However, resistant strains of S pneumoniae are increasingly common. Most resistant strains respond to fluoroquinolones such as levofloxacin (Levaquin), gemifloxacin (Factive), or moxifloxacin (Avelox).

In addition, other important causes of CAP, particularly in younger people, are atypical bacteria, which respond to macrolides (clarithromycin, azithromycin, or erythromycin), or newer fluoroquinolones.

In children, amoxicillin is the first line treatment in non-severe pneumonia. Macrolides may be considered for children with suspected atypical pathogens. Antiviral medications should be given to children with moderate to severe CAP with influenza infection as soon as possible.

It is prudent to follow up on outpatient treatment response within 48 to 72 hours of initiating treatment.

Antibiotic Treatments for Hospital-Acquired (Nosocomial) Pneumonia

A broad range of antibiotics is available for treating hospital-acquired pneumonias and more severe forms of the condition. Factors that may determine the choice of an antibiotic include:

Treatment of Viral Infections

There are not as many choices for treating viral pneumonia. Oseltamivir (Tamiflu), zanamivir (Relenza), and peramivir (Rapivab) have been the recommended drugs for influenza A or B infections, but some strains of influenza A are resistant to them. Generally, the use of these drugs is only recommended if they can be started in the first 48 hours of symptoms. Taken early, these medications may be effective in reducing the severity and duration of illness. However, treatment initiated even after 48 hours may benefit children with severe disease.

Intravenous immunoglobulins may be used in immunodeficient children who develop some viral pneumonias, as they have been shown to improve outcomes.

People with viral pneumonias are at risk for what are called "superinfections," which generally refers to a secondary bacterial infection, usually caused by S pneumoniae, S aureus, or H influenzae. Doctors most commonly recommend treatment with amoxicillin-clavulanate, cefpodoxime, ceftriaxone, cefuroxime, or a newer fluoroquinolone if these secondary infections occur.

People with pneumonia caused by varicella-zoster and herpes simplex viruses are usually admitted to the hospital and treated with intravenous acyclovir for 7 days.

No antiviral drugs have been proven effective yet in adults with RSV, parainfluenza virus, adenovirus, metapneumovirus, coronaviruses, or hantavirus. Treatment is largely supportive, with people receiving oxygen and ventilator therapy as needed.

As the treatment for SARS-CoV-2 is rapidly evolving, we do not have definite recommendations yet, but for severe cases, the antiviral remdesivir and corticosteroids can be utilized.

Treatment of RSV in Children

Ribavarin is the first treatment approved for RSV pneumonia, although it has only modest benefits. The American Academy of Pediatrics recommends this drug for certain children who are at high risk for serious complications of RSV.

Side Effects of Antibiotics

Most antibiotics have the following side effects (although specific antibiotics may have additional or fewer of these side effects):

Drug Classes


Beta-lactam antibiotics share common chemical features. They include penicillins, cephalosporins, and some newer similar medications. They interfere with bacterial cell walls.


Penicillin was the first antibiotic. There are many forms of this still-important drug:

Many people have a history of an allergic reaction to penicillin, however, that the allergy may not occur again in a significant number of adults. Skin tests are available to help determine if those with a history of penicillin allergies could use these important antibiotics.


Most of these antibiotics are not very effective against bacteria that have developed resistance to penicillin. They are classed according to their generation:

Other Beta-Lactam Agents

Ceftaroline, a cephalosporin, is the first beta-lactam active against MRSA and multidrug-resistant S pneumoniae.

Carbapenems include meropenem (Merrem), ertapenem (Invanz) and combinations (imipenem/cilastatin [Primaxin]). These drugs are used to treat a wide variety of bacteria. They are now used for serious hospital-acquired infections and bacteria that have become resistant to other beta-lactams.


Fluoroquinolones (quinolones) interfere with bacteria's genetic material to prevent them from reproducing.

S pneumoniae -- strains resistant to the "respiratory" fluoroquinolones are uncommon in the US, but resistance is dramatically increasing.

Many quinolones cause side effects, including:

Pregnant women should not take these medications. The drugs also enhance the potency of oral anti-clotting drugs.


Macrolides also affect the genetic material of bacteria. These medications include:

These antibiotics are effective against atypical bacteria such as mycoplasma and chlamydia. Macrolides are also used in some cases for S pneumoniae and M catarrhalis, but there is increasing bacterial resistance to these antibiotics.

ER azithromycin (Zmax) is the first anti-pneumonia antibiotic that can be given in a single dose. It is effective against Gram-positive, Gram-negative, and atypical bacteria. A single-dose ER antibiotic decreases the likelihood that a person will stop taking the antibiotic early, which rapidly contributes to the development of drug-resistant bacteria.


Tetracyclines inhibit the growth of bacteria. They include doxycycline, tetracycline, and minocycline. They can be effective against S pneumoniae and M catarrhalis, but bacteria that are resistant to penicillin are also often resistant to doxycycline. The side effects of tetracyclines include:


Aminoglycosides (gentamicin, tobramycin, and amikacin) are given by injection for very serious bacterial infections. Some are available in inhaled forms. Others can be applied in a solution directly to mucus membranes, skin, or body cavities. They can have very serious side effects, including:


Lincosamides prevent bacteria from reproducing. The only member of this group in clinical use is clindamycin (Cleocin). This antibiotic is useful against anaerobic bacteria, S pneumoniae and S aureus, but not against H influenzae.


Glycopeptides (vancomycin) are used for S aureus infections that have become resistant to standard antibiotics. The drug must be given intravenously for pneumonia and other infections beyond the intestinal tract. The newest glycopeptide, a derivative of vancomycin, is called telavancin (Vibativ). It has an indication for the treatment of hospital-acquired Gram-positive pneumonia when alternative treatments are not suitable.


Trimethoprim-sulfamethoxazole (Bactrim, Cotrim, and Septra) is less expensive than many other antibiotics. It is particularly useful for adults with mild bacterial upper respiratory infections who are allergic to penicillin. The drug is no longer effective against certain streptococcal strains. It should not be used in people whose infections occur after dental work, or in people who are allergic to sulfa drugs. Allergic reactions can be very serious.


Linezolid (Zyvox) is the first antibacterial drug in a new class of man-made antibiotics called oxazolidinones. It has been shown to work against certain aerobic Gram-positive bacteria. Dangerous drug interactions, however, can occur when taking this medication with other common medications, including cold medicines and certain antidepressants known as selective serotonin reuptake inhibitors (SSRIs).


Lefamulin (Xenleta) is the first antibacterial drug from the pleuromutilin class that was approved for the treatment of community-acquired pneumonia in adults. Pleuromulitins interfere with the production of proteins in bacteria. Lefamulin is given orally or by intravenous infusion in patients with community-acquired pneumonia caused by susceptible Streptococcus pneumoniae, Staphylococcus aureus (methicillin-susceptible isolates), Haemophilus influenzae, Legionella pneumophila, Mycoplasma pneumoniae, and Chlamydophila pneumoniae.

Other Medications

Tigecycline (Tygacil) is now approved for community-acquired bacterial pneumonia. It is given intravenously and works against most gram-positive organisms including MRSA. This drug can cause tooth discoloration in young children. It is not recommended for use during pregnancy, unless no other alternative is available. In 2010 the FDA announced a safety warning that there is increased risk of death when IV Tygacil is used compared to other antibiotics. Tygacil should be used in situations when alternative treatments are not suitable.

Inhaled polymyxin, a drug used in people with cystic fibrosis, is showing some effectiveness against pneumonia caused by multidrug-resistant Gram-negative bacteria, including pseudomonas and klebsiella.

Corticosteroid use in people with pneumonia is also under investigation. Corticosteroids impact the immune system, carbohydrate and protein metabolism, electrolyte balance, and stress response. They may help to speed recovery and resolve symptoms, but more research is necessary to suggest recommendations for populations.


Chest Tubes

Although most people with pneumonia do not need invasive therapy, it may be necessary in people with empyema or certain other complications.

Chest tubes are used to drain infected pleural fluid. Tubes are not typically required for pneumonia or abscesses. The tubes are inserted after the person receives a local anesthetic. They remain in place for 2 to 4 days. They are removed in one quick movement. This can be very distressing, although some people feel no discomfort. Complications of chest tubes include:

Removing the chest tubes may cause the lung to collapse. In this case, a chest tube may be needed to inflate the lung.

Chest tube insertion - series - Pleural cavity

Click the icon to see an image series about chest tube insertion.


Good Hygiene and Preventing Transmission

The best way to prevent serious respiratory infections such as pneumonia is to avoid sick people (if possible) and to practice good hygiene.

Colds and flu are spread primarily from infected people who cough or sneeze. People commonly transmit a cold when they shake hands. Washing hands frequently can prevent the spread of viral respiratory illnesses. Always wash your hands before eating and after going outside. Using ordinary soap is sufficient. Alcohol-based gels are also effective for everyday use, and may even kill cold viruses. If extreme hygiene is required, use alcohol-based rinses.

Antibacterial soaps add little protection, particularly against viruses. Wiping surfaces with a solution that contains 1 part bleach to 10 parts water is very effective at killing viruses.

Preventing Transmission of COVID-19

At this time there is no vaccine and no medication available that can prevent COVID-19. However, there are a number of ways to protect yourself and others around you from getting COVID-19. To help prevent the spread of COVID-19 within the community, the governments throughout the world and in the United States are recommending that people wear cloth masks or face coverings and practice social distancing. Steps to follow in preventing the spread of COVID-19 include:

If you have COVID-19 or have symptoms of it, you must isolate yourself at home and avoid contact with other people, both inside and outside your home, to avoid spreading the illness. This is called home isolation. Steps to follow in home isolation for COVD-19 include:

For the most up-to-date news and information about COVID-19, you can visit the following websites:

Centers for Disease Control and Prevention website. Coronavirus Disease 2019 (COVID-19).

World Health Organization website. Coronavirus Disease 2019 (COVID-19) Pandemic.

Changing Hospital Practices

Bacteria abound in hospitals and long-term care facilities. They are particularly able to cause disease in areas with the sickest patients, such as ICUs. Health care facilities are changing many of their practices and educating doctors, nurses, and therapists about reducing the likelihood of transmitting bacteria.

Viral Influenza Vaccines (Flu Shot)

Description of Vaccines

Injected vaccines against the flu ("flu shots") use inactivated (not live) viruses. The nasal spray influenza vaccine uses an attenuated (greatly weakened) live flu virus. Flu vaccines are designed to provoke the immune system to attack antigens contained on the surface of the virus. Antigens are foreign molecules that the immune system recognizes and targets for attack.

Timing and Effectiveness of the Vaccine

Each year, scientists decide which viruses are likely to circulate during the upcoming flu season and make recommendations for updated seasonal vaccines. Ideally, people should get a flu shot every October or November. However, it may take longer for a full supply of the vaccine to reach certain locations. In such cases, high-risk groups should get vaccinated first.

The US Centers for Disease Control and Prevention (CDC) Advisory Council recommends that, unless contraindicated, all people ages 6 months and older, unless contraindicated, get a flu shot every year. These universal recommendations simplify earlier recommendations for specific high-risk groups.

Older children and adults need only a single shot each year. However, children under age 9 years may need 2 shots, given 1 month apart the first time they receive the flu vaccine or if they have not previously received two doses during a flu season.

Some people have a higher risk of the disease.

If supplies are limited, people in high-risk groups, such as the following, should get a flu vaccine first:

Pneumococcal Vaccines

The pneumococcal vaccine protects against S pneumoniae bacteria, the most common cause of respiratory infections. There are 2 effective vaccines available:

Experts are now recommending that more people, including healthy older people, receive the pneumococcal vaccine, particularly in light of the increase in antibiotic-resistant bacteria.

Pneumococcal pneumonia

Click the icon to see an image of pneumococcal pneumonia.

Pneumococcal Vaccine in Young Children

The Food and Drug Administration (FDA) has approved the pneumococcal conjugate vaccine (Prevnar 13 or PCV13) for children 6 weeks to 17 years old for the prevention of pneumococcal pneumonia. PCV13 covers 13 types of pneumococci and replaces an earlier version, PCV 7. Children age 2 years or older who have medical conditions that increase the risk of pneumococcal pneumonia should also receive the pneumococcal polysaccharide vaccine PPSV23 at least 8 weeks after completing PCV 13 immunization.

Many experts now recommend the PCV 13 for all children up to age 5, and older children with certain medical conditions. Healthy children who received the PCV 7 vaccine will complete their scheduled doses with the newer PCV 13. The pneumococcal conjugate vaccine has now been added to the Recommended Childhood Immunization Schedule. Studies are suggesting that it prevents common ear infections, as well as pneumonia in children.

The recommended schedule of immunization for PCV13 in healthy children includes 4 doses, given at 2, 4, 6, and 12 to 15 months of age. It is recommended that immune-compromised children be revaccinated at certain intervals.

Pneumococcal Vaccine in Adults

In healthy adults age 65 years and older who have not previously received a pneumococcal vaccine, the Advisory Committee on Immunization Practices (ACIP) now recommends sequential administration of PCV 13 and the pneumococcal polysaccharide vaccine PPSV23 one year or more following the PCV 13 vaccine.

In adults who have previously received a PPSV23 vaccine, a single dose of PCV 13 should be given one year or more after the PPSV23.

The ACIP recommends adults ages 19 to 64 years who have heavy alcohol use, tobacco use, or have medical conditions including diabetes, heart, lung, or liver disease receive pneumococcal polysaccharide vaccine PPSV23.

Sequential administration of PCV 13 and PPSV23 is recommended in adults age 18 years or older who have any of the following medical issues: splenectomy or a condition affecting spleen function, an immunocompromised condition; a cerebrospinal fluid leak, or a cochlear implant. Adults with these medical issues should receive the PPSV23 vaccine 8 weeks or more following the PCV 13 vaccine.

Revaccination schedules vary depending upon age and medical condition.

Preventing Respiratory Syncytial Virus (RSV) Pneumonia in Children

Across the globe, RSV is the most common reason for acute lower respiratory infection in children under the age of 5 years. Parents often spread the infection to their baby. A simple way to help prevent RSV infection is to wash your hands often, particularly before touching your baby. It is important to make sure that other people, particularly caregivers, take precautions to avoid giving RSV to your baby. The following simple steps can help protect your baby:

Prevention of RSV

Two medications have been approved for protecting high-risk children against RSV pneumonia:

Other vaccines

Other vaccines that are part of the recommended immunization schedule for children and adolescents may protect against other causes of pneumonia:



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Review Date: 11/27/2020
Reviewed By: Denis Hadjiliadis, MD, MHS, Paul F. Harron Jr. Associate Professor of Medicine, Pulmonary, Allergy, and Critical Care, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
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