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For MRSA detection, nasal screening alone may be insufficient
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PHILADELPHIA – Conducting nasal screening alone to identify patients with methicillin-resistant Staphylococcus aureus may lead to some missed diagnoses, according to results of a study presented at the 109th General Meeting of the American Society for Microbiology, held here this week.
The results of the study, conducted by Choong Park, PhD, and Deborah Hixon, both from Inova Fairfax Hospital in Falls Church, Va., indicated that adding throat screening as a second test for MRSA helped to identify 12.3% more patients with MRSA.
The researchers screened all patients that were treated in intensive care units at their hospital between June and October 2008. Swabs from throat and both anterior nares were collected from 2,669 patients.
The overall prevalence rate of MRSA was 8.2% (220 patients). One hundred nineteen patients (4.4%) tested positive for MRSA from nasal and throat screening. But 74 patients (2.8%) tested positive for MRSA in the nasal screening alone and 27 patients (1%) tested positive for MRSA in the throat screening alone.
The researchers said these findings were important because if the nasal screening had been the only method of testing for MRSA, the 27 patients whose MRSA was detected by the throat screening alone would have remained undiagnosed.
“The results of this study show that nasal screening alone may be insufficient,” the researchers wrote. “The addition of throat screening increased the detection of positive MRSA by 12.3%.”
Park and Hixon also noted that the cost-effectiveness of using both methods of detection would be “difficult to assess” and that additional screening methods should also be analyzed. – by Jay Lewis
For more information:
- Park C. C-050. Presented at: The 109th General Meeting of the American Society for Microbiology. May 17-21, 2009. Philadelphia.
This is really confirmatory information; there is already an abundance of evidence to show that nasal screening alone is not sufficient to identify all MRSA – or MSSA – carriers. Throat cultures evidently add only a very modest increment of carriers. One wonders what additional increment might have been identified had additional sites been swabbed – eg, axilla and groin.
– Theodore C. Eickhoff, MD
Infectious Disease News Chief Medical Editor
In this day and age, with healthcare associated MRSA occurring in outpatient settings; and the emergence and spread of CA-MRSA as predominant community staphylococcal pathogen, screening protocols should ideally include specimens from both the nares and throat. The throat is a particularly important reservoir, as some CA-MRSA strains may only colonize a patient’s throat and not the nares. Unfortunately, rapid PCR tests for detection of MRSA on swab samples are only approved for use on nares specimens and not on throat specimens. This limitation in the rapid processing of throat specimens is a limitation to screening protocols that include nares and the throat.
This study also stresses the importance of treating everyone as if they might be colonized with a resistant pathogen: proper hand hygiene by healthcare workers for all patients, regardless of their MRSA colonization test status, is tantamount to preventing the spread of MRSA in hospitals.
– Keith Kaye, MD
Infectious Disease News Editorial Board member