Pneumonia is an infection of the lung tissue that can make it difficult to breathe due to inflammation, fluid, and pus. Viruses or bacteria, which are contagious, cause most forms of pneumonia.
Not all cases of pneumonia are contagious, however, and the period during which it can spread from one person to another depends on the cause of the infection.
Pneumonia refers to an infection in the lungs caused by certain germs, such as bacteria or viruses. When one person spreads germs that can cause pneumonia to someone else, the recipient can develop a range of respiratory infections, from mild cold symptoms to pneumonia.
A range of factors determine whether pneumonia is contagious:
Type of pneumonia
Most cases of pneumonia are due to the spread of bacteria and viruses. Bacteria are living organisms that respond to antibiotics. Viruses are tiny strands of protein and genetic material that cannot be treated with antibiotics. Both viruses and bacteria are contagious.
Pneumonia often develops after a person has had a different infection, such as a head cold. This makes a person more vulnerable to other types of infections. An infection that develops in the lungs is called pneumonia.
Some organisms are more likely to cause pneumonia than others. One common example is pneumococcal disease, a bacterial infection that can cause ear infections, sinus infections, infections of the brain and blood, and pneumonia.
Another type of bacteria called Mycoplasma pneumoniae can cause other forms of pneumonia. Mycoplasma bacteria are also contagious.
Less common causes of pneumonia include:
- inhaling food particles or contents from the intestinal tract
- some fungi
These forms of pneumonia are not contagious.
Length of infection
In most cases, infections are contagious for a few days before symptoms appear and for a few days after. The exact length of time a person is contagious depends on the type of microorganism causing the infection.
Some forms of pneumonia, such as pneumonia caused by mycoplasma, remain contagious for several weeks. If a person has pneumonia, they should speak to a doctor about how long the infection will be contagious.
People with bacterial pneumonia will usually be prescribed antibiotics that stop the infection from progressing. Pneumonia will usually stop being contagious a day or two after treatment begins.
A person is also considered contagious during a fever, so it is best to stay home from work or school until the fever is gone.
People who have been vaccinated against infections that can cause pneumonia, such as pneumococcal bacteria, are usually immune to those specific germs. Getting the vaccination can help prevent this type of infection from developing.
Although anyone can get pneumonia, some people are at greater risk. Pneumonia occurs when an infection develops within the lungs. It can cause complications with breathing and spread to other parts of the body such as the bloodstream.
People who are more likely to get pneumonia include:
- very young children and babies whose immune systems are not fully developed
- older people with weakened immune systems
- pregnant women
- people taking medications that suppress the immune system
- people with diseases that weaken the immune system, such as cancer, HIV, and AIDS
- people with autoimmune diseases, such as rheumatoid arthritis
- people with lung and respiratory conditions, such as chronic obstructive pulmonary disease (COPD), cystic fibrosis (CF), and asthma
People at risk of pneumonia need to be especially cautious around people who have recently had pneumonia or another respiratory infection.
Pneumonia is transmitted when germs from the body of someone with pneumonia spread to another person. This can happen in a variety of ways, including:
- Inhaling the infection. This can occur when a person with pneumonia coughs or sneezes and another person inhales the infected particles. This is more likely between people in close contact with each other, such as parents and children, or in poorly ventilated spaces, such as airplanes.
- Through the mouth or eyes. This can happen when a person touches a surface that an infected person has coughed or sneezed on. When a person with an infection coughs into their hand and then shakes another person’s hand, the second person can become infected if they touch their mouth or eyes without washing their hands.
Food particles and irritants from the intestinal tract can also cause pneumonia. This is called aspiration pneumonia and can occur when a person accidentally inhales these substances.
Fungal pneumonia typically develops when people inhale microscopic particles of fungus from the environment. People with weakened immune systems are more likely to develop this type of pneumonia.
A number of strategies can prevent the spread of pneumonia. The single most effective way to prevent the spread of viruses and bacteria is with frequent hand-washing, especially during the colder months.
People should wash their hands before eating, after using the bathroom, after touching someone else, before visiting people vulnerable to pneumonia, and upon returning home after going out in public.
Other strategies to prevent pneumonia include:
- staying up-to-date on all vaccinations, as well as getting a flu shot annually
- quitting smoking, since smoking makes the lungs more vulnerable to infection and affects the body’s immune system
- managing any chronic medical conditions, especially those that affect the immune system or lungs
- staying home from school or work when ill or with a fever
Most people recover from pneumonia without any lasting effects. In vulnerable people, pneumonia can be fatal. Worldwide, pneumonia accounts for 16 percent of deaths in children under 5. Older people and those with a weakened immune system are also more likely to experience serious complications.
Older people, people with serious illnesses, parents of newborns, and caregivers to sick people should make sure all visitors wash their hands. It is best that people with symptoms of a respiratory illness or fever do not visit a vulnerable person until their symptoms are gone.
Other strategies that can reduce the risk include:
- washing hands before eating, after touching people, and after going out in public
- disinfecting all surfaces in the home, particularly if someone has recently been sick
- keeping up-to-date on all vaccinations, especially any household members around infants who are too young to be vaccinated
- avoiding locations with inadequate air filtration during cold and flu season
Pneumonia killed more than 50,000 people in the United States in 2014. Despite this, around two-thirds of older adults do not get the recommended pneumococcal pneumonia vaccination to prevent pneumonia.
Pneumonia can be prevented, particularly in people who do not have chronic lung diseases. By avoiding sick people, staying home when ill, washing hands, and adopting basic health measures, such as getting vaccinated, it is possible to prevent this potentially fatal illness.