Pneumonia

Mild pneumonia may be healed by the body’s defense system.

Pneumonia is an inflammation of the airspace (alveoli; singular alveolus) in the lung most commonly caused by infections. Bacteria, viruses, or fungi (infrequently) can cause pneumonia. There are also a few noninfectious types of pneumonia that are caused by inhaling or aspirating foreign matter or toxic substances into the lungs.

Some cases of pneumonia are life-threatening. Around 50,000 people die each year of pneumonia in the U.S. Although anyone of any age can be affected, pneumonia is more common in elderly people and often occurs when the immune system becomes weakened via a prior infection or another condition.

Pneumonia is generally more serious when it affects older adults, infants, and young children, those with chronic medical conditions, or those with weakened immune function.

Sometimes, types of pneumonia are referred to by the type of organism that causes the inflammation, such as bacterial pneumonia, viral pneumonia, or fungal pneumonia. The specific organism name may also be used to describe the types of pneumonia, such as pneumococcal (Streptococcus pneumoniae) pneumonia or Legionella pneumonia.

Other types of pneumonia that are commonly referenced include the following:

• Aspiration pneumonia develops as a result of inhaling food or drink, saliva or vomit into the lungs. This occurs when the swallowing reflex is impaired, such as with brain injury or in an intoxicated person.
• Several types of bacteria, including Legionella pneumophila, Mycoplasma pneumoniae, and Chlamydophila pneumoniae, cause atypical pneumonia. It is sometimes called “walking pneumonia” and is referred to as atypical because its symptoms differ from those of other types of bacterial pneumonia.
• Pneumonia that arises from being on a ventilator for respiratory support in the intensive care setting is known as ventilator-associated pneumonia.

Causes of pneumonia include the following:

• Streptococcus pneumoniae, a type of bacteria, is the most common cause of pneumonia.
• Legionella pneumophila is the bacterial type that causes pneumonia known as Legionnaires' disease.
• Other bacteria types that can cause pneumonia include the bacteria that cause so-called “atypical” pneumonia, Legionella pneumophila, Mycoplasma pneumoniae, and Chlamydophila pneumonia.
• Haemophilus influenzae is a type of bacteria that can cause pneumonia. It most commonly causes disease in babies and children younger than 5 years of age. Adults 65 years or older, American Indians, and Alaska Natives are also at increased risk for developing H. influenzae disease.

The most common causes of viral pneumonia in adults are the influenza virus, respiratory syncytial virus (RSV), and SARS-CoV2 (the virus that causes COVID-19). Several different respiratory viruses cause pneumonia in children, including respiratory syncytial virus (RSV). While viral pneumonia tends to be less severe than bacterial pneumonia, it may cause serious problems in some patients. There is a risk of developing secondary bacterial pneumonia when viral pneumonia is present. Other virus types that can cause pneumonia include measles and varicella (chickenpox) viruses. Rarely, certain viruses may cause lethal pneumonia, including SARS-CoV2SARS-CoV (cause of severe acute respiratory syndrome) or MERS (Middle East respiratory syndrome); both diseases are caused by different coronaviruses.

Fungi that cause pneumonia include Cryptococcus, Histoplasma, and Coccidioides. In most individuals, these organisms don’t cause illness, but they can cause pneumonia in some people. Fungal infections are most common in those with weakened immune systems due to HIV/AIDS or those taking medications that suppress immune function. Another infection that is considered a fungal type of pneumonia is Pneumocystis jirovecii, formerly known as Pneumocystis carinii. This organism became known as a frequent cause of pneumonia in patients with HIV/AIDS.

The emphasis of this article is on the more common causes of infectious pneumonia, but others may be related to inflammatory and allergic conditions or caused by noninfectious lung irritants like inhalation of chemicals, foods, gasses, liquids, and/or dust. Electronic cigarette (e-cigarette or vape pen) use has been uncommonly associated with severe lung injury (e-cigarette or vape-associated lung injury [EVALI]) and lipoid pneumonia (lung injury and scarring due to aerosolized oils). Several substances commonly found in vape products are still being investigated for toxicity.

Several factors increase the risk of developing pneumonia, such as:

• A weakened immune system, either due to diseases such as HIV/AIDS or cancer or to medications that suppress immune function
• Infants and children 2 years of age or younger
• Age 65 and older
• Having a chronic disease such as pulmonary disease (including cystic fibrosis and COPD), sickle cell anemia, asthma, heart disease, or diabetes
• Swallowing or coughing problems, as may occur following a stroke or other brain injury
• Being a patient in an intensive care unit of a hospital, particularly if on ventilator support
• Malnutrition
• Cigarette smoking or electronic cigarette use (vaping)

Symptoms and signs of pneumonia may be mild or severe and depend upon someone's overall state of health and the type of organism causing pneumonia.

Severe symptoms of pneumonia include:

• Cough
• Chest pain when breathing or coughing
• Labored breathing or shortness of breath
• Coughing up phlegm
• Fever
• Chills
• Fatigue

Nausea, vomiting, and diarrhea are other possible symptoms that can accompany respiratory symptoms.

Infants and newborns may not show specific symptoms of pneumonia. Instead, the baby or child may appear restless or lethargic. A baby or child with pneumonia may also have a fever, cough, or vomit. Older adults or those with weak immune systems may also have fewer symptoms and a lower temperature. A change in mental status, such as confusion, can develop in older adults with pneumonia.

The incubation period for pneumonia depends on the type of organism causing the disease, as well as the characteristics of the patient, such as his or her age and overall health status. Most cases of pneumonia begin with symptoms similar to those of a cold that lasts longer than seven to 10 days and becomes more severe. The symptoms of pneumonia can occur from a few days to a week following flu-like symptoms.

The duration of symptoms varies according to the type of pneumonia and the underlying health status of the individual. In previously healthy people, pneumonia can be a mild illness that resolves within two to three weeks. In older adults and those with chronic diseases or other health problems, recovery may take six to eight weeks or longer.

Most types of bacterial pneumonia are not highly contagious. Even though it is possible to spread bacteria from one person to another, pneumonia typically occurs in people with risk factors or weakened immune defenses when bacteria that are normally present in the nose or throat invade the lung tissue. Any kind of bacterial or viral pneumonia has the potential to be contagious, but Mycoplasma pneumoniae and Mycobacterium tuberculosis (the cause of tuberculosis) are two types of bacterial pneumonia that are highly contagious. Breathing in infected droplets that come from patients who are coughing or sneezing can spread the disease to others.

It is impossible to say with certainty exactly how long an adult or child with pneumonia is contagious since this varies according to the type of germ or organism that caused pneumonia. This contagious period can range from one to two days to weeks. In general, while an infected person is coughing or sneezing, there is the potential to release contaminated droplets into the air.

Many bacterial types of pneumonia are much less contagious after antibiotics have been taken for about 24-48 hours. However, this period may vary for some organisms. For example, with tuberculosis, it can take two weeks or more of antibiotics before the person is no longer contagious. With viral pneumonia, the patient becomes less contagious after the symptoms have improved, especially fever. Some people with viral pneumonia may not be contagious after one to two days with no fever, but others may still shed some infectious virus particles for a much longer time.

You should call your doctor if you have a cough that doesn't improve, shortness of breath or difficulty breathing, chest pain, fever, or if you feel worse after having a cold.

In some cases, primary care physicians, including pediatricians, internists, and family medicine specialists, may manage the care of patients with pneumonia. In more severe cases, other types of specialists may be involved in treating the patient with pneumonia. These include infectious disease specialists, pulmonologists, critical care specialists, and hospitalists.

The diagnosis of pneumonia always begins with taking a medical history and performing a physical examination to look for characteristic signs. In particular, listening to the lungs may reveal areas where sound is diminished, wheezing or crackling sounds in affected areas.

Some commonly performed diagnostic tests are as follows:

• A chest X-ray can illustrate whether or not pneumonia is present, but it does not provide information about the organism responsible for the infection.
• In some cases, a chest CT scan may be performed. This will reveal more detail than the chest X-ray.
• Pulse oximetry measures the amount of oxygen in the bloodstream. The test involves a painless sensor attached to the finger or ear. Blood levels of oxygen may be reduced in pneumonia.
• Microbiology tests to identify the causative organism. Tests may be performed on blood or sputum. Rapid urine tests are available to identify Streptococcus pneumoniae and Legionella pneumophila. Cultures of blood or sputum not only identify the responsible organism but can also be examined to determine which antibiotics are effective against a particular bacterial strain.
• Bronchoscopy is a procedure in which a thin, lighted tube is inserted into the trachea and major airways. This allows the doctor to visualize the inside of the airways and take samples if needed. Bronchoscopy may be performed in patients with severe pneumonia or if pneumonia worsens despite antibiotic treatment.

Pneumonia can be classified or characterized in different ways. Healthcare professionals often refer to pneumonia based on the way that the infection is acquired, such as community-acquired pneumonia or hospital-acquired pneumonia.

• Community-acquired pneumonia (CAP), as the name implies, is a respiratory infection of the lung that develops outside of the hospital or healthcare environment. It is more common than hospital-acquired pneumonia. CAP is most common in winter and affects about 4 million people a year in the U.S.
• Hospital-acquired pneumonia (HAP) is acquired when an individual is already hospitalized for another condition. HAP is generally more serious because it develops in ill patients already hospitalized or under medical care for another condition. Being on a ventilator for respiratory support increases the risk of acquiring HAP. Healthcare-associated pneumonia is acquired from other healthcare settings, like kidney dialysis centers, outpatient clinics, or nursing homes.

Other classification systems for pneumonia describe the way the inflammatory cells infiltrate the lung tissue or the appearance of the affected tissue (see the following examples).

• Bronchopneumonia causes scattered, patchy infiltrates of inflammation in the air sacs throughout the lungs. It is more diffuse than lobar pneumonia.
• Lobar pneumonia causes inflammation of one lobe of a lung and typically involves all the airspace in a single lobe.
• Lipoid pneumonia is characterized by the accumulation of fats within the airspace. It can be caused by the aspiration of oils or associated with airway obstruction.

Antibiotic and antifungal medications are the treatment of choice for pneumonia caused by bacterial and fungal infections. The exact choice of medications depends on many factors, including the following:

• The organism responsible for the infection
• The likelihood that the organism is resistant to certain antibiotics
• The patient's underlying health condition

About 80% of cases of CAP can be managed at home with the patient taking oral antibiotics. There are numerous treatment regimens available. Initial treatment (before the causative organism has been identified) is called empiric treatment and is based on the organisms most likely to be responsible for the illness. Once the exact organism has been identified in the laboratory and susceptibility testing performed to determine which antibiotics are effective, the treatment regimen can be further individualized. Over-the-counter pain and fever-reducing medications may be recommended for some people in addition to antibiotics or antiviral drugs for symptom relief. Do not take cough or cold medications when suffering from pneumonia without a doctor's approval.

In around 20% of cases, CAP must be managed in the hospital, typically with intravenous antibiotics initially. HAP care is managed in the hospital, typically with intravenous antibiotics.

Antibiotics are not effective against viral pneumonia. Depending upon the type of virus that causes pneumonia, antiviral medications can provide benefits when started early in the course of the disease. For example, those at risk for pneumonia due to COVID-19 may be treated with antivirals to reduce the likelihood of hospitalization, including oral nirmatrelvir-ritonavir (Paxlovid) or intravenous remdesivir. The medications oseltamivir (Tamiflu) and zanamivir (Relenza) are used to treat influenza virus infections. Antifungal agents are used to treat most fungal pneumonia.

Most people with pneumonia improve after three to five days of antibiotic treatment, but a mild cough and fatigue can last longer, up to a month. Patients who require treatment in a hospital may take longer to see improvement.

Pneumonia can also be fatal. The mortality (death) rate is up to 30% for patients with severe pneumonia who require treatment in an intensive care unit. Overall, around 5%-10% of patients who are treated in a hospital setting die from the disease. Pneumonia is more likely to be fatal in the elderly or those with chronic medical conditions or a weakened immune system.

There are several potential complications of pneumonia. The infection that causes pneumonia can spread to the bloodstream, causing sepsis.

• Sepsis is a serious condition that can result in a lowering of blood pressure and failure of oxygen to reach the tissues of the body, resulting in the need for intensive care management.
• Another complication is the accumulation of fluid in the space between the lung tissue and the chest wall lining, known as a pleural effusion. The organisms responsible for pneumonia may infect the fluid in a pleural effusion, known as empyema.
• Pneumonia can also result in the formation of an abscess (collection of pus) within the lungs or airways.

It is not possible to prevent all types of pneumonia, but one can take steps to reduce the chance of contracting the condition by quitting smoking, practicing good hand-washing, and avoiding contact with people who have colds, the flu, or other infections.

A vaccine is available against the most common bacterial cause of pneumonia, Streptococcus pneumoniae (also known as pneumococcus).

The vaccine options for bacterial pneumonia continue to evolve for different individuals, as well as the recommended type and order of dosing. As of 2023, the vaccines include:

1. PPSV23 (Pneumovax), a pneumococcal polysaccharide vaccine against 23 types of pneumococcus
2. PCV15 (Vaxneuvance), a pneumococcal conjugate vaccine that protects against 15 types of pneumococcus
3. PCV20 (Prevnar20), a pneumococcal conjugate vaccine that protects against 20 types of pneumococcus

Side effects of pneumococcal vaccines in children include drowsiness, temporary loss of appetite, redness, swelling, or tenderness where the shot was given. Mild fever and irritability are other common side effects. Adults receiving pneumococcal vaccines have reported pain, redness, rash, and swelling where the shot was given; also mild fever, fatigue, headache, chills, or muscle pain.

Any type of vaccine has the potential to cause an allergic reaction, which can be severe, but this side effect is very rare. This would happen within minutes to a few hours after receiving the vaccine.

When to see the doctor for pneumonia vaccine side effects

Serious side effects after receiving the pneumonia vaccination are rare, but not impossible. Call your doctor if you experience the following:

• Allergic reaction
  • Severe allergic reactions only occur in about one in a million shots. An allergic reaction to vaccinations typically happens within a few minutes to a few hours after receiving the shot. Seek emergency medical attention at the first sign of an allergic reaction to the pneumonia vaccine.
• Feeling faint or dizzy
  • If you or your child feel dizzy, have vision changes, or have ringing in your ears, call your doctor.
• Severe pain
  • Some people may experience severe pain in the shoulder and have difficulty moving their arms after the pneumonia vaccine. Notify your doctor if this happens to you.

PCV15 and PCV20 are currently approved by the U.S. Food and Drug Administration for people 65 years of age or older and people 6 weeks to 64 years of age with certain medical conditions.

PPSV23 is FDA-approved for all adults 65 years of age or older and for people who are 2 years of age or older and at high risk for pneumococcal disease (for example, those with sickle cell disease, HIV infection, or other immunocompromising conditions). PPSV23 is also recommended for use in adults 19-64 years of age who smoke cigarettes.

There is no evidence about the safety of conjugate (PCV) vaccine use in pregnancy. Women who need the vaccine should be vaccinated before pregnancy, if possible.

Determining the type and order of immunization with these vaccines may be complicated and depends on age, individual health conditions, and whether a prior conjugate or PPSV23 vaccine was received. Therefore CDC has developed a tool, PneumoRecs VaxAdvisor, to help determine which vaccines are needed.

Seasonal influenza vaccines are available yearly and are recommended to decrease the chance of contracting influenza. Vaccines against RSV and SARS-CoV2 are available and recommended to reduce the chance of severe viral pneumonia and hospitalization in those at risk. Vaccines against the measles virus and varicella virus, two viruses that can also cause pneumonia, are also available. The common side effects of these vaccines are similar to those of the pneumonia vaccine.