Pneumonia: Causes, Risk Factors, Symptoms, Tests and Treatment

Pneumonia is an infection of one or both lungs that makes the air sacs fill with fluid or pus. It can be mild or severe, depending on the germ causing it, your age and your overall health.

Causes

Bacteria, viruses and fungi can all cause pneumonia.

• Bacteria are the most common cause. Bacterial pneumonia can arise on its own or after certain viral infections, such as a cold or the flu. Culprits include Streptococcus pneumoniae, Legionella pneumophila (the cause of what is often called Legionnaires' disease), Mycoplasma pneumoniae, Chlamydia pneumoniae and Haemophilus influenzae.
• Viruses that infect the respiratory tract — respiratory syncytial virus (RSV), some cold and flu viruses, and SARS-CoV-2, the virus that causes COVID-19 — can cause it too. Viral pneumonia is often mild and clears up within a few weeks, but it can be serious enough to need hospital care, and it raises the risk of bacterial pneumonia as well.
• Fungi cause pneumonia more often in people with chronic health problems or weakened immune systems. Types include Pneumocystis pneumonia (PCP), coccidioidomycosis (which causes valley fever), histoplasmosis and cryptococcus.

Who is at risk

Anyone can get pneumonia, but risk is higher with:

• age: children 2 and under, and adults 65 and older
• exposure to certain chemicals, pollutants or toxic fumes
• smoking, heavy drinking or malnourishment
• a hospital stay, especially in intensive care, and more so when sedated or on a ventilator
• lung disease or a weakened immune system
• trouble coughing or swallowing, from a stroke or other condition
• a recent cold or flu

Symptoms

Symptoms range from mild to severe: fever, chills, a cough that usually brings up phlegm, shortness of breath, chest pain when breathing or coughing, nausea or vomiting, and diarrhea. They can vary by group:

• Newborns and infants may show no sign of infection, or may vomit, have a fever and cough, and seem ill, listless or restless.
• Older adults and people with serious illness or weak immune systems may have fewer and milder symptoms, even a lower than normal temperature. Older adults sometimes show sudden changes in mental awareness.

Complications

Pneumonia can lead to serious problems, including bacteremia (bacteria entering the bloodstream, which can lead to septic shock), lung abscesses (pockets of pus in the lungs), disorders of the pleura (the tissue covering the lungs and lining the chest cavity), kidney failure and respiratory failure.

Diagnosis

Because its symptoms can resemble a cold or the flu, pneumonia can be hard to spot, and it may take time to realize something more serious is going on. A provider may use a medical history, a physical exam including listening to the lungs, a chest x-ray, and blood tests such as a complete blood count or a blood culture.

For people in the hospital, with serious symptoms, who are older or who have other health problems, further tests may include a sputum test, a chest CT scan (which shows how much of the lungs is affected and can reveal abscesses or pleural effusions), a pleural fluid culture, pulse oximetry to measure blood oxygen, and bronchoscopy to look inside the airways.

Treatment and recovery

Treatment depends on the type, the germ and the severity. Antibiotics treat bacterial pneumonia and some fungal pneumonia, but not viral pneumonia; antiviral medicines are sometimes prescribed for viral pneumonia, and antifungal medicines treat other fungal types. Severe symptoms or a risk of complications may mean hospital care, with extra treatment such as oxygen if blood oxygen is low. Some people feel better within a week; for others recovery takes a month or more.

Prevention

Vaccines help prevent pneumonia caused by pneumococcal bacteria or the flu virus. Good hygiene, not smoking and a healthy lifestyle may also help.

Sources

Based on "Pneumonia", MedlinePlus, U.S. National Library of Medicine, drawing on the National Heart, Lung, and Blood Institute; a work of the United States government in the public domain.