Risk Factors:

Risk factors for pneumonia often depend on the specific type of disease.

Risk Factors for Institutional- and Hospital-Acquired (Nosocomial) Pneumonia

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:

• The elderly and very young.
• People with chronic or severe medical conditions, such as lung problems, heart disease, neurologic disorders, and cancer.
• People who have had surgery, particularly people over age 80. Among the surgical procedures that pose a particular risk are removal of the spleen (splenectomy), abdominal aortic aneurysm repair, or operations that impair coughing.
• People who have been 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.
• People who have received 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 especially dangerous in people who are already ill.

Risk Factors for Community-Acquired Pneumonia (CAP)

CAP is the most common type of pneumonia. It develops outside of the hospital. Each year 2 - 4 million people in the US 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. In patients with COPD, vaccination with the pneumococcal vaccine can substantially reduce the risk of developing pneumonia or decrease its severity.

Bronchitis is the inflammation of the bronchi, the main air passages to the lungs. It generally follows a viral respiratory infection. Symptoms include coughing, shortness of breath, wheezing, and fatigue.

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:

• Adult and pediatric cancers, especially leukemia and Hodgkin's lymphoma
• Chemotherapy
• Organ transplantation

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:

• Children
  • Patients with asthma, COPD, and compromised immune systems
• The elderly

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:

• Abnormalities of the muscles of the esophagus
• Illnesses such as Parkinson's disease
• Neurologic disorders involving the esophagus
• Stroke
• Surgical or radiation treatment for cancers of the mouth, throat, or esophagus
• Traumatic brain injuries

All of these may increase the risk of aspiration pneumonia.

Dementia. The impaired vigilance while swallowing contributes to an increased risk of aspiration pneumonia.

Gastroesophageal Reflux Disease. Gastroesophageal reflux disease (GERD) is a condition in which acids from the stomach move up into the esophagus. This 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 appear to have an above-average risk for:

• Chronic bronchitis
• Chronic sinusitis
• Emphysema
• Lung scarring (pulmonary fibrosis)
• Recurrent pneumonia

If a person inhales fluid (aspirates) from the esophagus into the lungs, it may trigger inflammation in these upper passages.

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.

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.

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:

• Abnormalities in muscle coordination of the mouth and throat
• Asthma
• Certain genetic disorders such as sickle-cell disease, cystic fibrosis, and Kartagener's syndrome, which result in poorly functioning cilia, the hair-like cells lining the airways
• Gastroesophageal reflux disorder (GERD)
• Impaired immune system
• Inborn lung or heart defects
• Infection with the respiratory syncytial virus (RSV)
• Leukemia