September 27, 2011 (Chicago, Illinois) — Carriers of Staphylococcus aureus in the nose do not have a raised risk for death after an S aureus infection. Marin Schweizer, PhD, an associate in general internal medicine at the University of Iowa in Iowa City, and colleagues performed what they believe is the first meta-analysis to look for such an association among infected patients, she reported at here at the 51st Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC).
In a poster presentation, the investigators pointed out that previous studies have found that colonized patients were more likely to die than uncolonized ones, but those studies found an association when all patients were considered, not just ones infected with S aureus. Therefore, although nasal colonization appears to increase the risk for infection, and people infected with S aureus are more likely to die, it was unknown whether nasal colonization was an independent risk factor for death among infected people.
The investigators reviewed 140 article abstracts and 36 articles in detail and then pooled the odds ratios (OR) from 8 independent study populations that looked for an association between colonization and mortality of infected patients. One of the 8 included study populations consisted of patients in neonatal intensive care.
Using a random effects model, the authors found no association between colonization and mortality in the infected population (pooled OR, 1.25; 95% confidence interval [CI], 0.43 - 3.66; n = 8; heterogeneity P = .002).
Restricting the analysis to infection-attributable mortality, a nonsignificant trend toward a protective effect of colonization against mortality emerged (pooled OR, .42; 95% CI, 0.10 - 1.84; n = 3; heterogeneity P = .14).
A previous study to which the investigators referred also showed that people with nasal colonization were less likely to die if they became infected with S aureus. Dr. Schweizer explained to Medscape Medical News that one possible explanation for the lower risk for death could be that these people had developed enhanced immunity to the bacterium before they became infected. Another idea is that colonizing strains may be less invasive than noncolonizing ones.
Aninda Das, MD, a member of Healthcare Partners Medical Group in Mission Hills, California, and an assistant clinical professor in infectious diseases at Children's Hospital of Los Angeles, California, commented to Medscape Medical News that a study strength was that it included diverse patient populations, ranging in age from neonates to adults.
"Our level of immune response is very different at different stages of our lives, so what may apply to someone who is older may not apply to someone who is of neonatal age," he warned. "To actually now paint them with one brush and say that this is what we should do for all age groups from what we see now" is not a good idea, he said. Dr. Das noted that given such diverse populations, there may be other confounding factors that could contribute to the findings.
He commended the researchers for recommending performing a larger study to more rigorously investigate any association of nasal colonization and risk for or protection from death.
This study received no commercial support. Dr. Schweizer has received research support from Pfizer. Dr. Das has disclosed no relevant financial relationships.
51st Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC): Abstract K-222. Presented on September 17, 2011.
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