Pneumonia is an infection that causes the air sacs in one or both lungs to fill with fluid or pus. Each year, more than 250,000 Americans are hospitalized with pneumonia, and about 50,000 die from the disease.

Signs and symptoms of pneumonia can vary depending on the type and severity, but they typically include:

There are many different types of pneumonia – and most of them can be contagious. Here’s what you need to know about the types of pneumonia, how they spread, and how to protect yourself.

Which types of pneumonia are contagious?

Pneumonia is contagious when it is caused by infectious pathogens, like bacteria or viruses. This is the case with most types of pneumonia, including:

  • Bacterial pneumonia is the most common type of pneumonia in adults and is typically caused by the bacterium Streptococcus pneumoniae. Bacterial pneumonia can occur on its own, or as a result of a viral cold or flu. You might also catch bacterial pneumonia during a hospital stay for another illness, because your immune system is already weakened and you are more susceptible.
  • Methicillin-resistant staphylococcus aureus (MRSA) pneumonia is a type of bacterial pneumonia caused by antibiotic-resistant bacteria. Those who work or live in crowded spaces with frequent skin-to-skin contact, like nursing homes, daycare centers or hospitals, are at an increased risk for this type of pneumonia.
  • Viral pneumonia is the most common cause of pneumonia in children younger than five years old. Any virus that infects the respiratory tract can cause viral pneumonia, but the flu virus is the most common cause of viral pneumonia in adults, according to the National Heart, Lung and Blood Institute (NHLBI).
  • Walking pneumonia, also known as atypical pneumonia, generally describes a mild case of pneumonia, often caused by a common bacterium known as Mycoplasma pneumonia. This type of pneumonia accounts for about 10% to 40% of pneumonia cases not acquired in hospitals or health care facilities.

If you have bacterial pneumonia, you'll remain contagious until you've been on antibiotics for 24 to 48 hours. If you have viral pneumonia, you will be contagious until your symptoms subside.

However, pneumonia is not contagious when it is caused by a foreign substance, like when food, drink, or saliva enters the lungs and causes inflammation. This is called aspiration pneumonia, which accounts for about 5% to 15% of pneumonia cases acquired outside of health care facilities.

Risk factors for aspiration pneumonia include anything that may make swallowing more difficult, such as:

  • Poor gag reflex after a stroke or brain injury
  • Receiving medication, like general anesthesia, meant to put you in a deep sleep
  • Drinking large amounts of alcohol

How do you get pneumonia?

The way pneumonia develops and spreads depends on the type and cause, says David Cutler, MD, family medicine physician at Providence Saint John's Health Center.

Many types of microbes - including bacteria, viruses, and fungi - can cause pneumonia. These germs commonly spread when an infected person coughs or sneezes and expels bacterial or viral droplets. These droplets could land on a surface, such as a table or a doorknob, infecting others who come into contact with the surface and then touch their eyes or mouth. Or, you may breathe in respiratory droplets from an infected person.

Most of the time, your immune system can effectively fight off these germs. But sometimes they overpower your body's natural defenses and invade your lungs. In response, your body produces white blood cells to fight off the attackers, filling the lung's air sacs with pus or cellular debris and causing pneumonia.

Adults older than 65 and children under the age of two are at an increased risk of developing pneumonia. This is because an older adult's immune system isn't as robust as a young adult's, and a young child's immune system is still developing.

Those who are immunocompromised or take medication that suppresses the immune system, like oral corticosteroids, are also at an increased risk of pneumonia because their bodies may not be able to fight off the germs that cause the infection.

How to prevent the spread of pneumonia

To reduce your risk of getting or spreading pneumonia, you should do the following:

  • Practice good hygiene. Wash your hands with soap and water for at least 20 seconds after touching frequently used public surfaces. In addition, coughing into your elbow - and not your hands - can help decrease the spread of pathogens that cause pneumonia.
  • Boost your immune system. To keep your immune system strong and protect yourself against illness, you should exercise regularly and eat a healthy diet full of fruits and vegetables. Read more about how to boost your immune system.
  • Don't smoke. Smoking damages your lungs and reduces their ability to defend against germs. A 2016 analysis of 27 studies examining the effect of tobacco smoke on developing pneumonia found that smokers older than 65 are at a 64% increased risk for pneumonia.

Get the necessary vaccines

In addition, there are several vaccines that can help protect against some viruses and bacteria that cause pneumonia, Cutler says.

These include the following:

  • Pneumococcal pneumonia vaccine. The Centers for Disease Control and Prevention (CDC) recommends this vaccine for babies and children younger than two years old and adults age 65 and older.
  • Influenza vaccine. The CDC recommends everyone six months and older get a flu vaccine every year to protect against the infectious diseases and related health complications, like pneumonia.
  • Hib vaccine. The CDC recommends this vaccine for all children younger than five years old. It protects against the Haemophilus influenzae type b (Hib) bacteria that can cause pneumonia and meningitis.

Takeaways

Most people who have pneumonia are effectively treated at home, according to the NHLBI. But pneumonia can also be a life-threatening condition, especially for older adults or people with chronic lung problems, like asthma.

Overall, getting vaccinated, practicing good hygiene, and staying away from someone you know is sick can reduce your risk for developing pneumonia, Cutler says.

If you do experience signs of pneumonia, like difficulty breathing, chest pain, and a persistent fever of 102 degrees Fahrenheit or higher, you should seek immediate medical attention.

Related articles from Health Reference: