Pneumonia is a lower respiratory lung infection that causes inflammation in one or both lungs.

Air sacs in your lungs called alveoli can then fill up with fluid or pus, causing flu-like symptoms that can persist for weeks or cause rapid deterioration of breathing leading to hospitalization. Pneumonia doesn't respond to over-the-counter cold and sinus medicines.

Pneumonia comes in different forms and is caused primarily by bacteria or viruses, which are contagious, and less commonly by fungi or parasites.

The type of germ contributes to how serious the illness can become and how it’s treated. The severity of an infection depends on many factors, including your age and overall health, as well as where you may have acquired the illness.

Causes and Risk Factors of Pneumonia

How do you get pneumonia? The majority of the germs that cause infection are spread from person to person through droplets, from coughing or sneezing.

Young children and people older than 65 are the most vulnerable to pneumonia, notes Mayo Clinic.
According to the National Heart, Lung, and Blood Institute (NHLBI), you're also at higher risk for pneumonia if you have any of the following conditions:
  • Asthma
  • Cystic fibrosis
  • Chronic obstructive pulmonary disease (COPD)
  • A weakened immune system due to human immunodeficiency virus (HIV) or cancer

People who smoke are at higher risk for pneumonia, as are people on immunosuppressive medications, and people who are frequently in close, crowded spaces with others, such as college students and military personnel.

RELATED: 10 Pneumonia-Related Terms You Need to Know

What Types of Pneumonia Are There?

Your doctors will try to classify your type of pneumonia to help guide your treatment.

Community-Acquired Pneumonia (CAP)

This is the most common form of pneumonia because you can catch it in public places, such as at school or work. It can be caused by bacteria, viruses, or fungi, according to the National Library of Medicine.

You can also develop CAP after you get a viral infection, such as a cold or the flu or the SARS-CoV-2 virus, which causes COVID-19.

RELATED: What You Need to Know About the COVID-19 Pandemic

CAP ranges from mild to serious and, if left untreated, can lead to respiratory failure or death.

Bacterial CAP is usually more serious than other types and is more common among adults. Atypical pneumonia, often called walking pneumonia, is a milder form often caused by the bacteria Mycoplasma pneumoniae. Walking pneumonia symptoms include sore throat, persistent, dry cough, fatigue, and headaches, and fever, per the Cleveland Clinic.

Various types of bacteria can be responsible for the illness. In most cases, the bacteria will enter the lung during inhalation, then travel into the bloodstream, potentially causing damage to other organs and systems in the body.

Streptococcus pneumoniae, also known as pneumococcal pneumonia, can be treated with antibiotics. But according to the Centers for Disease Control and Prevention (CDC), many types of bacteria, including some S. pneumoniae (pneumococcus), are resistant to those antibiotics, which can lead to treatment failures. Pneumococcal pneumonia causes an estimated 150,000 hospital admissions a year in the United States.
Risk factors for bacterial CAP include:
  • Having an underlying lung disease, like asthma or COPD
  • Having a systemic disease, such as diabetes
  • Having a weakened immune system
  • Abusing alcohol
  • Smoking

Depending on how sick you are and whether you have any other health conditions, your doctor may treat you for a presumptive bacterial pneumonia with antibiotics either at home or in the hospital.

Getting a vaccination against pneumococcal pneumonia reduces your risk for bacterial CAP, per the CDC.There are two different pneumonia vaccines; ask your doctor if you qualify for either.
Viral CAP, particularly the respiratory syncytial virus (RSV), is the most common cause of pneumonia in children younger than one year old, notes the CDC.
Although cases of viral pneumonia are often relatively mild, infections caused by certain flu viruses can be very serious, notes the ALA.So can infections caused by coronaviruses, such as severe acute respiratory syndrome ( SARS) and SARS-CoV-2, the virus that causes COVID-19. (See the section below for information on COVID-19 and Pneumonia).

Antibiotics are ineffective against viral pneumonia. Your doctor will most likely treat the symptoms — fever, cough, and dehydration.

You or your child may need to be hospitalized if your viral pneumonia symptoms become severe.

Fungal CAP is most common in people with an underlying health problem or a weakened immune system, including those with HIV or acquired immunodeficiency syndrome (AIDS) and people undergoing treatment for cancer, according to the NHLBI.

Hospital-Acquired Pneumonia

As the name suggests, this develops during a hospital stay for a different health problem. People who are on machines to help them breathe are particularly prone to developing hospital-acquired pneumonia, notes MedlinePlus.

Hospital-acquired pneumonia usually needs to be treated in the hospital with intravenous antibiotics.

Aspiration Pneumonia

This can develop after a person inhales food, drink, vomit, or saliva into their lungs. Once your lungs have been irritated by breathing in food or stomach contents, a bacterial infection can develop.

A strong gag reflex or cough will usually prevent aspiration pneumonia, but you may be at risk if you have a hard time swallowing or have a decreased level of alertness.

This type of pneumonia can also occur in older people with poor swallowing mechanisms, such as stroke victims, according to MedlinePlus.

Aspiration pneumonia causes inflammation without bacterial infection. These pneumonias can sometimes be difficult to treat, especially because the patients are often sicker to begin with.

Some conditions that may put you at risk for aspiration pneumonia include:

  • Loss of alertness due to medicines, illness, or surgery (getting anesthesia)
  • Overuse of alcohol
  • Old age
  • Poor gag reflex due to brain injury or stroke
  • Coma

Symptoms of aspiration pneumonia include cough, increased sputum, fever, confusion, and shortness of breath.

Treatment may include breathing assistance and intravenous antibiotics given in the hospital.

You can prevent complications by not eating or drinking before surgery, working with a therapist to learn how to swallow without aspirating, and avoiding heavy use of alcohol.

Opportunistic Infection

Finally, Pneumocystis pneumonia is a fungal pneumonia that is extremely rare in healthy people, according to the CDC, but develops in people with a weakened immune system; it’s often referred to as an opportunistic infection.

You're at risk for this type of pneumonia if you have a chronic lung disease, have HIV or AIDS, or have had an organ transplant, notes the CDC.

How Is Pneumonia Diagnosed?

“It’s a tough disease to diagnose,” says Marie Budev, DO, a pulmonologist and the medical director of the lung transplant program at the Cleveland Clinic in Ohio. “Age makes a big difference, as well as a person’s immune status … and, of course, the symptoms themselves.” Pneumonia symptoms often mimic those of the common cold and the flu, as well as acute bronchitis, an inflammation of the lining of your bronchial tubes (that carry air to and from your lungs).


Bronchitis vs. Pneumonia: Why They’re Related and How They’re Different

A pneumonia diagnosis is based on your medical history, a physical exam, and certain test results. Your doctor determines which type of pneumonia you have based on how you became infected, what your X-ray or lung exam reveals, and which kind of germ is responsible for your infection.

When taking your medical history, your doctor will ask about any signs and symptoms you've been having, any recent travel or exposure you may have had, and whether you've had flu or pneumonia vaccinations.

During a physical exam, your doctor will check your vital signs and listen to your lungs with a stethoscope. “Decreased breath sounds is an indication of a lot of inflammation,” says Michelle Barron, MD, a professor in the division of infectious diseases at University of Colorado School of Medicine in Aurora.

If your doctor suspects pneumonia, they may order further diagnostic tests, such as a chest X-ray to help determine the extent of the infection. Blood tests and an analysis of the patient’s sputum can pinpoint what’s causing the pneumonia. Pulse oximetry measures the oxygen level in your blood (which may be low if pneumonia is affecting your lungs).

For people over 65 or for those whose pneumonia isn't clearing, a doctor might order a computerized tomography (CT) scan, which shows more detail of the lungs than a chest X-ray. In severe cases, a pleural fluid culture may also be taken — needle is inserted into the pleural area, between the lungs and the chest wall, to obtain a fluid sample, which is then analyzed to help figure out what's causing the infection, according to Mayo Clinic.


According to the ALA, most cases of pneumonia can be successfully treated, though full recovery can take weeks.
Pneumonia can be life-threatening or fatal, especially in elderly, frail people who may have other medical condition, notes Harvard Health Publishing.

Duration of Pneumonia

According to the ALA, some people can return to their normal routines within a week of treatment for pneumonia. For others, full recovery may take over a month.

Recovery depends on what type of pneumonia you have and how severe it is, and the underlying condition of your lungs. Per the NHLBI, most people with bacterial pneumonia treated with antibiotics begin to improve and have fewer symptoms after one to three days. It's important, though, to continue taking the full course of antibiotics, even if you're feeling better. Otherwise, the pneumonia could return.

Viral pneumonia usually improves in one to three weeks.
Most kids improve in 7 to 10 days with treatment, but those with severe pneumonia may require treatment for two to three weeks, notes MedlinePlus.

Prevention of Pneumonia

There’s no sure way to prevent pneumonia, but there are measures you can take, including pneumonia vaccines for some forms of the infection, and following sensible hygiene rules, to reduce your risk of being infected.

Practice good hygiene. Simple precautions, such as washing your hands frequently, covering your nose and mouth with a tissue when you cough or sneeze, and disposing of used tissues cut down exposure and spread of germs.


Why Proper Hand-Washing Is Essential During Cold and Flu Season

Don’t smoke. “Smokers are at a much greater risk of getting pneumonia because the protective mechanisms that your lungs set up to escalate debris out of your lungs are just paralyzed by tobacco,” says Jason Turowski, MD, a pulmonologist and associate director of the adult cystic fibrosis program at the Cleveland Clinic in Ohio.

Get vaccinated. Pneumococcal vaccines protect against one of the most common causes of bacterial pneumonia. The flu shot can help avoid influenza-related pneumonia and COVID-19 vaccines can lower your risk for pneumonia related to the coronavirus. Getting vaccinations “is the most important thing you can do,” Dr. Turowski says.

Complications of Pneumonia

Complications are more common in children, seniors, and people who are already challenged with other serious diseases, according to the NHLBI. Possible complications include the following:

  • Respiratory failure is when a patient needs a breathing machine or ventilator to stay alive. A more severe form of respiratory failure is acute respiratory distress syndrome (ARDS); this has been associated with COVID-19.
  • Sepsis is a condition in which bacteria from the lungs gets into your blood, causing uncontrolled inflammation in the body in response to infection; sepsis can lead to organ failure.
  • Lung abscesses are areas of pus that form inside or around the lung. Sometimes antibiotics can take care of them, but surgery or an interventional radiologic procedure may be required to drain them.
  • Kidney, liver, and heart damage can result when these organs don’t get enough oxygen or if your immune system responds negatively to the infection.

Related Conditions and Causes of Pneumonia

Influenza, or the flu, is a common cause of pneumonia, especially among people whose immune systems are compromised in some way. The flu usually doesn't lead to pneumonia, but when it does, the outcomes are much worse and can be fatal, notes the ALA.
Certain chronic medical conditions that affect your respiratory system can make you more vulnerable to pneumonia. These include COPD and asthma. If you develop pneumonia and have one of these conditions, symptoms may be more severe and recovery may take longer, according to the ALA.

Resources We Love

Favorite Orgs for Essential Pneumonia Info

American Lung Association (ALA)

The ALA offers a thorough review of pneumonia, explaining exactly what it is, the symptoms, treatment options, and tips on prevention. The site also presents questions to ask your doctors to determine your risk and vaccines to consider.

American Thoracic Society

This nonprofit focuses on improving care for pulmonary (lung-related) diseases, critical illnesses, and sleep-related breathing disorders. As part of its patient education information series, they provide an extensive summary of pneumonia, covering causes, diagnosis, treatment, and concerns.

Centers for Disease Control and Prevention (CDC)

The CDC not only delivers the essential facts on causes, management, and prevention, the federal agency also connects to studies on the spread of the illness and methods to reduce its prevalence. The CDC stresses that smoking is a prominent risk factor for lung infection and offers resources and support to quit smoking, including advice from former smokers.

Healthy Children

Children under age 2 and people over 65 are two groups that are most likely to develop pneumonia. This organization, created by the American College of Pediatrics, covers the essentials that parents need to know when it comes to their kids and pneumonia. Recommendations on vaccinations are detailed.

National Heart, Lung, and Blood Institute (NHLBI)

This site addresses all major pneumonia concerns, including risk factors, screening and protection, symptoms and complications, diagnosis, and treatment. The NHLBI also explains how to live with the infection, how to participate in clinical trials for new medication, and methods to manage the illness.

Stop Pneumonia

This organization raises awareness about pneumonia’s deadly impact on children around the world. It focuses on promoting interventions to protect against, prevent, and treat the illness. The site reviews important vaccines and practices that can help ward off the disease for all young people.

Favorite Orgs That Can Help Fight Pneumonia

Senior Living

Those over age 65 have a higher risk of getting pneumonia than younger adults. They may be especially susceptible to community-acquired pneumonia, spread among large populations of elderly people in settings such as assisted living facilities. This organization, devoted to finding the best products and services for seniors, publishes advice on how older adults should handle prevention and care.

United Against the Flu

Influenza is a common cause of pneumonia. Several national healthcare organizations and the CDC are collaborating in an effort called United Against the Flu to stress the importance of getting immunized. The group’s website supplies resources and details on the vaccination.

Editorial Sources and Fact-Checking

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  • Pneumonia: Diagnosis and Treatment. Mayo Clinic. June 13, 2020.
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  • COVID-19 and Lung Damage. Johns Hopkins Medicine. April 12, 2021.
  • Mycoplasma Pneumoniae Infection: Antibiotic Treatment and Resistance. Centers for Disease Control and Prevention. March 25, 2016.
  • FastStats: Pneumonia. Centers for Disease Control and Prevention. September 13, 2021.
  • Daily Updates of Totals by Week and State: Provisional Death Counts for Coronavirus Disease 2019 (COVID-19).  Centers for Disease Control and Prevention. October 26, 2021.
  • What Is the Connection Between Influenza and Pneumonia? American Lung Association. October 23, 2020.
  • The Connection Between Pneumonia and Lung Disease. American Lung Association. November 12, 2018.
  • Torres A, Cilloniz C, Niederman MS, et al. Pneumonia. Nature Reviews Disease Primers. April 8, 2021.


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