Risk factors for pneumonia often depend on the specific type of disease.
Pneumonia that is contracted in the hospital is called hospital-acquired or nosocomial pneumonia. It affects an estimated 5 - 10 of every 1,000 hospitalized patients every year. More than half of these cases may be due to strains of bacteria that have developed resistance to antibiotics. In fact, methicillin-resistant Staphylococcus aureus and multidrug-resistant Pseudomonas aeruginosa are leading causes of death from hospital-acquired pneumonia. Those at highest risk:
Hospitalized patients are particularly vulnerable to Gram-negative bacteria and staphylococci, which can be especially dangerous in people who are already ill.
CAP is the most common type of pneumonia. It develops outside of the hospital. Each year 2 - 4 million people in the U.S. develop CAP, and 600,000 are hospitalized. The elderly, infants, and young children are at greatest risk for the disease.
Chronic Lung Disease. Chronic obstructive lung disease (COPD), which includes chronic bronchitis and emphysema, affects 15 million people in the U.S. This condition is a major risk factor for pneumonia. Long-term use of corticosteroid inhalers may increase the risk of pneumonia in COPD patients. Patients with other types of chronic lung diseases, such as bronchiectasis and interstitial lung diseases are also at increased risk for getting pneumonia, and are more likely to have complications.
People With Compromised Immune Systems. People with impaired immune systems are extremely susceptible to pneumonia. It is a common problem in people with HIV and AIDS. A wide variety of organisms, including Myobacterium species, Histoplasma capsulatum, Coccidioides immitis, Aspergillus species, cytomegalovirus, and Toxoplasma gondii, can cause pneumonia.
In addition to AIDS, other conditions that compromise the immune system include:
Patients who are on corticosteroids or other medications that suppress the immune system are also prone to infection.
Also, drugs that treat gastroesophageal reflux (GERD) may slightly increase one's risk for community-acquired pneumonia. Patients at high risk for pneumonia should take gastric acid-suppressing drugs only when necessary and at the lowest possible dose. This association is strongest with protein pump inhibitors (PPIs) such as Prilosec and Nexium. Reducing levels of germ-killing stomach acid may allow germs to spread in the upper gastrointestinal tract and move into the respiratory tract. The risk posed by these medications is highest in:
Researchers have found that the risk is strongest when people have recently begun treatment with PPIs, and lessens over time.
Swallowing disorders, including dysphagia. Difficulty swallowing has a variety of causes, including:
All of these may increase the risk of aspiration pneumonia.
Dementia. The lack of ability to concentrate while swallowing contributes to an increased risk of aspiration pneumonia. Elderly patients with dementia who are treated with antipsychotic drugs for psychosis have a 60% increased risk of developing pneumonia. Researchers are not sure why these drugs increase the pneumonia risk.
If a person inhales fluid (aspirates) from the esophagus into the lungs, it may trigger inflammation in these upper passages.
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.
Drug and Alcohol Abuse. 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 start at the injection site and spread through the bloodstream to the lungs.
Certain children have a higher-than-normal risk for pneumonia and pneumonia that returns. Conditions that predispose infants and small children to pneumonia include:
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