Risk factors for methicillin-resistant Staphylococcus aureus in patients with community-onset and hospital-onset pneumonia

OBJECTIVES

The risk factors for methicillin-resistant Staphylococcus aureus (MRSA) pneumonia have not been fully characterized and are likely to be different depending on whether infection is acquired in the community or the hospital.

METHODS

We conducted a case-control study of 619 adults hospitalized between 2005 and 2010 with either MRSA or methicillin-sensitive S. aureus (MSSA) pneumonia. Patients with a respiratory culture within 48 h of hospitalization had community-onset pneumonia whereas patients with a culture collected after this time point had hospital-onset pneumonia.

RESULTS

Among patients with community-onset disease, the risk for MRSA was increased by tobacco use (OR 2.31, CI 1.23-4.31), chronic obstructive pulmonary disease (OR 3.76, CI 1.74-8.08), and recent antibiotic exposure (OR 4.87, CI 2.35-10.1) in multivariate analysis while patients with hospital-onset disease had an increased MRSA risk with tobacco use (OR 2.66, CI 1.38-5.14), illicit drug use (OR 3.52, CI 2.21-5.59), and recent antibiotic exposure (OR 2.04, CI 3.54-13.01). Hospitalization within the prior three months was associated with decreased risk (OR 0.64, CI 0.46-0.89) in multivariate analysis.

CONCLUSIONS

This study suggests there are common and distinct risk factors for MRSA pneumonia based on location of onset. The decreased risk for MRSA pneumonia associated with recent hospitalization is unexpected and warrants further investigation.

SUMMARY

This case-control study showed that there are common and distinct risk factors associated with MRSA pneumonia depending on whether the infection onset is in the hospital or in the community. Recent hospitalization was unexpectedly shown to be associated with decreased risk for MRSA pneumonia and warrants further investigation.

Penicillin-nonsusceptible Streptococcus pneumoniae at San Francisco General Hospital

Positive pneumococcal cultures of specimens from adult inpatients at San Francisco General Hospital (SFGH) during the period of 11 August 1994 through 31 December 1996 were identified retrospectively. Of the isolates recovered, 15.5% were not penicillin-susceptible (MIC, > or =.1 microg/mL). A case-control study was performed to evaluate risk factors for colonization or infection with penicillin-nonsusceptible Streptococcus pneumoniae (PNSP) and outcomes. Cases (n = 65) were adult inpatients with a positive culture for PNSP, and controls (n = 411) were adult inpatients with a positive culture for penicillin-susceptible pneumococci (PSSP) and no evidence of PNSP. Cases were less likely to have pneumococcal bacteremia (15.4% versus 39.4%; P<.001) and less likely to have pneumonia (50.8% versus 68.9%; P = .006). In a multiple logistic regression model, recent hospital admission and absence of bacteremia were independent predictors of penicillin-nonsusceptibility. Human immunodeficiency virus infection, mortality, and length of hospitalization were not significantly different among cases and controls. These data suggest that PNSP may be less virulent (cause less pulmonary infection) and/or less invasive (cause fewer bloodstream infections) than PSSP at SFGH.