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Pneumonia Center

Pneumonia Causes and Risk Factors

How do you get pneumonia?
People most commonly contract pneumonia from viruses and/or bacteria that enter the body through the mouth or nose, or through infections already in the bloodstream. Pneumonia can also develop after a cold, flu, or other illness through an infection that is already in the bloodstream. For example, the microorganisms that cause pneumonia may live in the body for some time before they make you ill. Alternatively, pneumonia is transmitted via droplets in the air after other people cough and/or sneeze. You may also get pneumonia by breathing in organisms from the environment.

What causes pneumonia?
Over 100 types of germs (microorganisms) can cause pneumonia. These include different kinds of bacteria, viruses, and, less often, fungi. However, it is often difficult or impossible to identify the specific microorganism which causes pneumonia.
The most common causes of pneumonia include:

Bacterial - Bacteria are the most common causes of pneumonia. Dozens of different types of bacteria can cause pneumonia and are the most common cause of pneumonia in adults. This type of pneumonia often affects one lobe, or area, of a lung. The most common types of bacterial pneumonia include:

  • atypical pneumonia (Mycoplasma pneumonia)
  • chlamydia pneumonia
  • hemophilus influenza
  • klebsiella pneumoniae
  • legionnaire's disease ( Legionella pneumonia)
  • pneumocystis carinii pneumonia
  • streptococcus pneumoniae

Fungal - Fungal infections can lead to fungal pneumonia but are relatively infrequent in the U.S. as they originate from fungi found in the soil. Serious fungal infections are most common in people with weak immune systems. Fungal infections are most frequently caused by the following fungi: histoplasmosis, coccidiomycosis, blastomycosis, aspergillosis, and cryptococcosis.

Nosocomial – Nosocomial organisms are resistant bacteria that have been exposed to strong antibiotics and have developed to them. If nosocomial organisms enter the lungs, a person may develop a serious pneumonia infection. Examples of this type of bacteria include the organisms “staphilococcus aureus” and “pseudomonas”.

Other - Anthrax, plague, and tularemia also may cause pneumonia, but their occurrences are rare.

Viral – Viral pneumonia is caused by viruses, especially the flu virus and do not respond to antibiotics. Most cases of viral pneumonia are mild and get better after 1-3 weeks without treatment. Although viral pneumonia is usually less severe than bacterial pneumonia, it can damage the lungs and may allow bacteria to cause a more serious infection that requires hospitalization. The most common types of viruses that cause viral pneumonia include: adenoviruses, herpes simplex virus, rhinovirus, influenza virus (flu), respiratory syncytial virus (RSV), severe acute respiratory syndrome (SARS), and/or parainfluenza virus.

Risk factors
A risk factor is something that increases the chance that you will contract a disease or condition. Risk factors may not be a direct cause of a particular disease, but seem to be associated with its development in some way. Risk factors for pneumonia often depend on the specific type of disease and/or microorganism which causes it. However, some people are more likely than others to develop pneumonia. Risk factors for pneumonia include:

Age People younger than 1 year or older than 65 are more likely to develop pneumonia. In particular, babies and newborns are at increased risk of breathing mucus or saliva from the nose or mouth, liquids, or food from the stomach into the lungs. However, one-third of cases of pneumonia occur in people over the age of 65.

Alcohol or drug use- Alcohol and drug use or abuse is closely associated with the development of pneumonia. First, alcohol acts as a sedative and diminishes the reflexes that trigger coughing and sneezing. Alcohol also interferes with white blood cells that destroy bacteria and other microbes.

Diet – Pneumonia occurs more frequently in people who are malnourished.

Drug use - Intravenous drug abusers are at risk for pneumonia from infections that start at the injection site and spread through the bloodstream to the lungs.

Ethnicity – People of Native Alaskan or certain Native American ethnicities are more at risk of developing pneumonia.

Hospitalization – People who are hospitalized in an intensive care unit are more likely to develop pneumonia than those who are not.

Housing People who live on military bases and college students living in dormitories are at higher-than-average risk for pneumonia.

Medical history – People diagnosed with flu, chronic bronchitis, emphysema, asthma, respiratory illnesses, chronic obstructive pulmonary disease (COPD), chronic illnesses (heart or lung disease), stroke, viral pneumonia are at risk of getting bacterial pneumonia.

Medications – People who use medicines for gastroesophageal reflux disease (GERD) are at higher risk of pneumonia.

Season - Most pneumonia infections occur in the autumn or winter.

Smoke and environmental pollutants - The risk for pneumonia in people who smoke more than a pack a day is three times that of nonsmokers. Also, people who are chronically exposed to secondhand cigarette smoke are also at risk. Chronic exposure to certain chemicals (eg, work in construction or agriculture) such as toxic fumes, industrial smoke, and other air pollutants may also damage cilia function, which is a defense against bacteria in the lungs.

Weakened immune system – People with weakened or impaired immune systems are at higher risk of developing pneumonia than those with strong immunity. Some weakened immune systems can be caused by medical condition such as AIDS, malnutrition

Do you know how to identify the symptoms of pneumonia? Early identification and diagnosis is key to receiving the best treatment available. While some of the symptoms of pneumonia are well known, such as coughing and chest, there are additional symptoms to look for. Continue reading the next section for more information about symptoms of pneumonia.

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