Is pneumonia contagious?

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Published: February 26, 2016
Last reviewed: December 22, 2017

Pneumonia by itself is not contagious. From someone who has pneumonia, you do not catch pneumonia but only the microbes, which may then, in your case, cause no disease at all, a disease other than pneumonia, such as the flu, or pneumonia.

To get pneumonia, you do not need to be in contact with someone who has pneumonia. If you have a weak immune system, you can get pneumonia by inhaling microbes that normally live in your own mouth. You can get a type of pneumonia called Legionnaires’ disease, by inhaling water mist contaminated by the Legionella bacteria but not from the infected people. You can get fungal pneumonia by inhaling the fungi from the soil but much less likely from individuals with fungal pneumonia.

What are the risk factors for pneumonia?

  • Age under 2. Risk factors in infants include premature birth, zinc or vitamin A deficiency, lack of measles immunization and non-exclusive breastfeeding [1].
  • Age over 65
  • Acute viral infection, such as influenza (the flu) or measles
  • Chronic health conditions, such as asthma, chronic obstructive pulmonary disease (COPD), alcoholism, liver cirrhosis, malnutrition, teeth or gum infection (periodontitis), sickle cell anemia, diabetes mellitus, congestive heart failure, weak immunity (HIV/AIDS, removed spleen, cancer, leukemia), neurological diseases with impaired cough reflex, cystic fibrosis or being in wheelchair or bedridden
  • Hospital stay, especially when being on a mechanical ventilator in the intensive care unit, or after a major surgery (mainly brain, neck, chest or upper abdominal surgery) [33]
  • Smoking tobacco [4], cocaine (crack) or marijuana (weed) [5]
  • Drugs: prolonged steroid therapy [33,34,35], chemotherapy, immunosuppressant therapy associated with organ transplantation, proton pump inhibitors
  • Crowded environments (college dorms, daily care units, nursing homes, military), mostly during winter and early spring (bacterial and viral pneumonia) or late summer or autumn (Mycoplasma pneumonia) [30]
  • Living near big hospitals or hotels with cooling towers (Legionnaires’ disease)
  • Exposure to bird/bat droppings
  • Pregnancy [2]
  • Genetic susceptibility [6]
  • Other references: [1,7,8,9,26]

There is insufficient evidence about low body temperature (hypothermia) [10] or exposure to cold and dry air [3,11,12,13] as risk factors for pneumonia.

How can you get viral pneumonia?

Viral pneumonia usually develops as a complication of flu, bronchitis or rarely an infection of upper respiratory tract, such as common cold, mainly in young children, older adults and individuals with weak immunity [2].

If you are healthy and you are in close contact with someone who has viral pneumonia, you will more likely get the flu or other viral diseas rather than pneumonia [2,29].

How can you get bacterial pneumonia?

If you have poor immunity, flu, viral pneumonia or you are in intensive care unit on mechanical ventilation, you can get bacterial pneumonia by inhaling bacteria from your own nose or throat [22,26] or by being in prolonged and close (<3 feet or 1 meter) contact with someone who has bacterial pneumonia and coughs and sneezes [14,30].

If you are otherwise healthy, it is not very likely you will get pneumonia after being in contact with someone who has bacterial pneumonia [17].

Intravenous drug users can get pneumonia from the Staphylococcus aureus bacteria, which normally live on their skin and which–during a drug injection–enter the blood and from there the lungs [26].

A spread of the microbes from other infected internal organs (bowel, kidney, liver, heart valves) to the lungs can also cause pneumonia.

How can you get atypical (walking) pneumonia?

You can get atypical pneumonia by inhaling bacteria, such as Mycoplasma pneumoniae or Chlamydophila pneumoniae, when you are in close contact with someone who has atypical pneumonia and coughs and sneezes. Mycoplasma may not be very contagious, but outbreaks of pneumonia in crowded settings can occur [18,19].

The bacterium Legionella, which causes atypical pneumonia called Legionnaires’ disease, is not spread from person to person but by aerosolized water from cooling towers, air conditioners, hot tubs, whirlpools and showers, mainly in the buildings with complex water systems, such as hospitals and hotels [21]. The infection can occur year round but more commonly during the summer [32].

How can you get fungal pneumonia?

Fungi, such as Coccidioides and Histoplasma, which can cause pneumonia, rarely spread among otherwise healthy individuals but you can inhale them from the bird, bat and rat droppings in the soil, especially in the farms in the Mississippi River and Ohio River Valley and southwestern United States [25].

If you have a weak immune system, for example, due to HIV/AIDS or chemotherapy, you can get fungal pneumonia by inhaling the fungi, such as Candida, that normally live in your own mouth or from Pneumocystis jirovecii that normally lives in your lungs (opportunistic infection) [16,27].

How can you get aspiration pneumonia?

Aspiration means the entrance of fluid or solid material into your lungs. This can happen if you have an impaired gag reflex due to a neurological disease or if you vomit while unconscious, for example, while being severely drunk. When the material you have aspired is contaminated by bacteria (usually from your own mouth), you can develop bacterial pneumonia [31].

There is a chance that you get bacterial pneumonia when you are in close contact with someone who has developed aspiration pneumonia and coughs and sneezes.

Rarely, you can get pneumonia after inhaling dust from the skin or feathers of cats, cattle, sheep, goats (Q fever, anthrax pneumonia) or birds (bird flu, psittacosis).

How long does contagiousness in pneumonia last?

It is not known for how long does contagiousness in pneumonia last. In general, a person less likely spreads microbes after the onset of antibiotic treatment or after a drop of high temperature, that is usually after 2-10 days [15,24].

Can pneumonia spread from a mother to her baby?

During delivery, a newborn can contract the bacterium Chlamydia trachomatis from the vaginal canal of the infected mother and develop pneumonia [20].

Pregnant women are at increased risk of getting pneumonia [2]. Some viruses that cause pneumonia in mothers, for example, Influenza A virus (H1N1 – pandemic flu, but less likely H3N2 – seasonal flu) [28] , HIV and Varicella-zoster virus (chicken pox), can cross the placenta and cause pneumonia or other complications in the unborn babies [23].

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