Risk Factors for Antibiotic-Resistant Healthcare-Associated Pneumonia

John G. Bartlett, MD


January 26, 2009

This Viewpoint examines the risk factors for antibiotic-resistant pneumonia related to inpatient and outpatient healthcare, and provides guidance to identify patients at risk for resistant pneumonias.

Prediction of Infection Due to Antibiotic-Resistant Bacteria by Select Risk Factors for Health Care-Associated Pneumonia

Shorr AF, Zilberberg MD, Micek ST, Kollef MH
Arch Intern Med. 2008;168:2205-2210

Article Summary

Shorr and colleagues retrospectively reviewed patients hospitalized from 2003 through 2005 who developed healthcare-associated pneumonia, in order to define the bacteriology and risk factors for resistant bacteria in this population. The investigators used standard methods to define pneumonia and used the following 4 categories to define "healthcare-associated": (1) hospitalization within the previous 90 days; (2) residence in a nursing home or long-term care facility; (3) long-term hemodialysis; and (4) immunosuppression related to long-term use of steroids, HIV infection, or chemotherapy. Resistant bacteria included methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa, extended-spectrum beta lactamase-producing Klebsiella pneumoniae, and nonfermenting gram-negative bacilli.

The analysis included 639 patients; resistant pathogens were detected in 289 cases (45%). The major pathogens were the following:

  • MRSA in 157 (25%);

  • Streptococcus pneumoniae in 130 (20%)

  • P aeruginosa in 120 (19%); and

  • Other gram-negative bacilli in 47 (6%).

Factors associated with resistant bacteria as defined were analyzed by logistic regression that showed 4 important independent variables ( Table ).

On the basis of these observations, investigators assigned scores to the 4 variables as noted in the last column of the Table. With a final score of 0-2, the probability of infection with resistant pathogens was about 20%; for a point total of 3-5, the probability was approximately 55%; and for 6 or more points, it was nearly 80%.

The authors concluded that healthcare-associated pneumonia is commonly caused by resistant bacteria and that the scoring system they propose may be useful to identify patients who are most likely to harbor these resistant organisms.


Healthcare-associated pneumonia is a relatively newly recognized category of community-acquired pneumonia (CAP). It represents a middle position between hospital-acquired pneumonia and CAP in terms of anticipated pathogens. This analysis is among the relatively few studies to define the bacteriology of this newly recognized category, which accounts for a substantial portion of CAP cases. It should be noted that the current Infectious Diseases Society of America (IDSA) and the American Thoracic Society (ATS) recommendations for patients in this category are for empiric use of ceftriaxone, a fluoroquinolone, ampicillin-sulbactam, or ertapenem. These agents would generally be suboptimal therapy for a majority of patients according to this review.

Also of note, the major resistant pathogens found in this study should be easily detected with expectorated sputum cultures. The bad diagnostic reputation of expectorated sputum is based on the experience with Streptococcus pneumoniae, which is fragile, difficult to detect in a sea of "green strep," and infamous for false-negative cultures. This is simply not the case with Staphylococcus aureus and aerobic gram-negative rods. Thus, the significant messages from this study include the potential value of routine cultures with sensitivity tests, and the importance of being alert to these possible resistant pathogens, such as P aeruginosa and MRSA, based on Gram stain, especially in patients with the risk factors noted above.



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