Risk Factors
Risk factors for pneumonia often depend on the specific type of disease.
Risk Factors for Community-Acquired Pneumonia (CAP)
CAP is the most common type of pneumonia. It develops outside of the hospital. Each year between two and four million people in the US develop CAP, and 600,000 people are hospitalized. The elderly, infants, and young children are at greatest risk for the disease.
Risk Factors for Hospital-Acquired (Nosocomial) Pneumonia
Pneumonia that is contracted in the hospital is called hospital-acquired or nosocomial pneumonia. It affects an estimated 5 to 10 out of every 1,000 hospitalized patients every year.
Certain individuals, such as the elderly, the very young, and those with chronic or severe medical conditions, are at higher risk.
In addition, the following conditions within the hospital put patients at higher risk:
- Surgery, particularly in people over the age of 80. Among the surgical procedures that pose a particular risk are splenectomy (removal of the spleen), abdominal aortic aneurysm repair, or operations that impair coughing.
- Being in the intensive care unit (ICU). This is particularly true for newborns or patients on breathing machines (mechanical ventilators). In one study, 10% of ICU patients on a breathing machine developed pneumonia. Such patients who lie flat on their backs are at particular risk for aspiration pneumonia. Raising the patient up may reduce this risk.
- Sedation. Hospital patients who receive sedatives also have a higher risk of developing nosocomial pneumonia.
Hospitalized patients are particularly vulnerable to gram-negative bacteria and staphylococci, which can be particularly dangerous in people who are already ill.
Medical Conditions that Pose Risks for Pneumonia
Chronic Lung Disease. Chronic obstructive lung diseases, including chronic bronchitis and emphysema, affect 15 million people in the U.S. This condition is a major risk factor for pneumonia.
Click the icon to see an image of emphysema.
People With Compromised Immune Systems. People with impaired immune systems are extremely susceptible to pneumonia. In addition to AIDS, other conditions that compromise the immune system include organ transplantation, chemotherapy, and cancers, especially leukemia and Hodgkin's disease. Patients who are on corticosteroids or other medications that suppress the immune system are also prone to infection.
Gastroesophageal Reflux Disease. Gastroesophageal reflux disease (GERD) is a condition in which acids from the stomach move up into the esophagus. This action is called reflux. Current studies indicate an association between GERD and various problems that occur in the sinuses, ears, nasal passages, and airways of the lung. People with GERD also appear to have an above-average risk for chronic bronchitis, chronic sinusitis, emphysema, pulmonary fibrosis (lung scarring), and recurrent pneumonia. If a person inhales fluid (aspirates) from the esophagus into the lungs, serious pneumonia can occur. GERD may contribute to these conditions by triggering inflammation in these upper passages.
However, GERD drugs may increase one's risk. Patients at high risk for pneumonia should take gastric acid-suppressing drugs only when necessary and at the lowest possible dose.A 2004 study found that the use of gastric acid-suppressing drugs raises the risk of developing community-acquired pneumonia. The highest risks were associated with proton pump inhibitors (PPIs) such as Prilosec and Nexium, but H2-receptor antagonists (e.g., Tagamet, Pepcid) also elevated risk. The researchers theorize that reducing levels of germ-killing stomach acid allow germs to spread in the upper gastrointestinal tract and move into the respiratory tract. The risk posed by these medications is highest in the elderly, children, and patients with asthma, chronic obstructive pulmonary disease, and compromised immune systems.
Click the icon to see an image of gastric reflux.
Factors Associated with a Higher Risk in Healthy Adults
Dormitory or Barrack Conditions. Recruits on military bases and college students living in dormitories are at higher than average risk for Mycoplasma pneumonia. These groups are at lower risk, however, for more serious types of pneumonia.
Smoke and Environmental Pollutants. The risk for pneumonia in people who smoke more than a pack a day is three times that of nonsmokers. Those who are chronically exposed to secondhand cigarette smoke, which can injure airways and damage the cilia, are also at risk. Quitting smoking reduces the risk of dying from pneumonia to normal, but the full benefit takes 10 years to be realized. Toxic fumes, industrial smoke, and other air pollutants may also damage cilia function, which is a defense against bacteria in the lungs.
Drugs and Alcohol. Alcohol or drug abuse is strongly associated with pneumonia. These substances act as sedatives and can diminish the reflexes that trigger coughing and sneezing. Alcohol also interferes with the actions of macrophages, the white blood cells that destroy bacteria and other microbes. Intravenous drug abusers are at risk for pneumonia from infections that originate at the injection site and spread through the blood stream to the lungs.
Specific Risk Factors for Recurrent Pneumonia in Children
Certain children have a higher-than-normal risk for pneumonia and recurrence. Conditions that predispose infants and small children to pneumonia include:
- Impaired immune system
- Gastroesophageal reflux disorder
- Inborn lung or heart defects
- Abnormalities in muscle coordination in the mouth and throat
- Asthma
- Certain genetic disorders such as sickle-cell disease, cystic fibrosis, and Kartagener's syndrome, which results in malfunctioning cilia, the hair-like cells lining the airways
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