Pneumonia risk factors

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Editor(s)-in-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Priyamvada Singh, M.D. [2]Philip Marcus, M.D., M.P.H.[3]

Overview

The risk factors for pneumonia include: smoking, age, immuno-suppression, exposure to chemicals, underlying lung disease, and exposure to chemicals.

Risk Factors

Obstruction

• When part of the airway (bronchi) leading to the alveoli is obstructed, the lung is not able to clear fluid when it accumulates. This can lead to infection of the fluid resulting in CAP.
• One cause of obstruction, especially in young children, is inhalation of a foreign object such as a marble or toy. The object is lodged in the small airways and pneumonia can form in the trapped areas of lung.
• Another cause of obstruction is lung cancer, which can grow into the airways blocking the flow of air.

Lung Disease

• Smoking, and diseases such as emphysema, result in more frequent and severe bouts of CAP.
• In children, recurrent episodes of CAP may be the first clue to diseases such as cystic fibrosis or pulmonary sequestration.

Immune Problems

• People who have immune system problems are more likely to get CAP.
• Risk factors for increased mortality from community acquired pneumonia are: active malignancy, immuno-suppression, neurological disease, congestive heart failure, coronary artery disease, and diabetes mellitus
• People who have AIDS are much more likely to develop CAP. Pneumonia could be the first manifestation of an underlying undiagnosed HIV. It is thus recommended by the Center for Disease Control (CDC) that all patients aged 13 to 64 in a medical setting regardless of known risk factors be screened for HIV. The American College of Physicians and HIV Medicine Association recommends expanding screening for HIV from age 13 to 75 , .
• Other immune problems range from severe immune deficiencies of childhood such as Wiskott-Aldrich syndrome to less severe deficiencies such as common variable immunodeficiency.
• Elderly people are affected with increased incidence and severity of community acquired pneumonia. It is the fifth most common cause of death among individuals who are > 65 years of age, and fourth in individuals who are 85 years or older. The clinical picture in elderly could be subtle and could present only as delirium without any fever, cough or sputum. Therefore, a high index of suspicion should be kept in these groups of people.

Risk Factors Related to Specific Causative Pathogens in Community-acquired Pneumonia

Condition	Most Common Pathogens
Alcoholism	Streptococcus pneumoniae, oral anaerobes, Klebsiella pneumoniae, Acinetobacter spp, Mycobacterium tuberculosis
COPD	Haemophilus influenzae, Pseudomonas aeruginosa, Legionella spp, S. pneumoniae, Moraxella catarrhalis, Chlamydophila pneumoniae
Smoking	Haemophilus influenzae, Pseudomonas aeruginosa, Legionella spp, S. pneumoniae, Moraxella catarrhalis, Chlamydophila pneumoniae
Aspiration	Oral anaerobes, Gram-negative enteric bacteria
Lung Abscess	Community-acquired MRSA, M. tuberculosis, oral anaerobes, atypical mycobacteria, endemic fungal infection
Early HIV infection	S. pneumoniae, H. influenzae, M. tuberculosis
Late HIV infection	S. pneumoniae, H. influenzae, M. tuberculosis, Pneumocystis jirovecii, Cryptococcus, Histoplasma, Aspergillus, atypical mycobacteria (especially Mycobacterium kansasii), P.aeruginosa
> 2 weeks of cough with whoop or vomiting	Bordetella pertussis
Structural lung disease	P. aeruginosa, Burkholderia cepacia, S. aureus
IV drug use	S. aureus, anaerobes, M. tuberculosis, S. pneumoniae
Bioterrorism	Bacillus anthracis (anthrax), Yersinia pestis (plague), Francisella tularensis (tularemia)
Endobronchial obstruction	S. pneumoniae, anaerobes, H influenzae, S. aureus
Table adapted from IDSA/ATS Guidelines for CAP in Adults

Exposure to Animals

Animals	Most Common Pathogens
Bat or bird droppings	Histoplasma capsulatum
Birds	Chlamydophila psittaci
Rabbits	Francisella tularensis
Farm animals or parturient cats	Coxiella burnetti (Q fever)
Table adapted from IDSA/ATS Guidelines for CAP in Adults

Travel

Condition	Most Common Pathogens
Hotel or cruise ship stay	Legionella spp
Travel to southwestern US	Coccidioides spp, Hantavirus
Travel to southeast or east Asia	Burkholderia pseudomallei, avian influenza, SARS
Table adapted from IDSA/ATS Guidelines for CAP in Adults