Abstract

Background : The BD GeneOhm MRSA PCR assay (Becton Dickinson, USA) is a qualitative realtime PCR test for rapid detection of nasal colonization of methicillin-resistant Staphylococcus aureus (MRSA). We evaluated the performance of BD GeneOhm MRSA PCR assay versus MRSASelect (Bio-Rad, France) and broth enrichment cultures for detection of MRSA from nasal swabs. Methods : From August 2008 to January 2009, 295 nasal swabs were taken from patients in intensive care units and transported to the laboratory with BD CultureSwab Liquid Stuart Single Swab (Becton Dickinson, USA). The swabs were inoculated onto MRSASelect first and then suspended into GeneOhm sample buffer: 100 $\mu$L of the suspension was inoculated into 6.5% NaCl-tryptic soy broth (Becton Dickinson, USA), which was subcultured on MRSASelect after overnight incubation (TSBS). Performances of GeneOhm MRSA and MRSASelect were compared to TSBS. Results : With GeneOhm MRSA, 125 swabs (44.6%) were positive for MRSA, 13 (4.4%) were unresolved, and 2 were not determined. With MRSASelect and TSBS 86 (29.4%) and 106 swabs (36.2%), respectively, were positive. The sensitivity, specificity, and positive and negative predictive value of GeneOhm MRSA were 85.8%, 77.5%, and 72.8% and 93.5%, respectively, and corresponding values for MRSASelect were 78.3%, 94.8%, and 96.5% and 88.9%. Of the 33 patients whose 34 specimens were found false positive in GeneOhm MRSA, 23 patients were MRSA-positive either previously or subsequently to this study. All of the 10 patients with false-negative specimens in GeneOhm MRSA PCR assay were previously MRSA or methicilln-resistant coagulase negative staphylococci (MRCNS)-positive and were treated for MRSA, but they became MRSA-positive after 1 to 4 negative surveillance cultures. Conclusions : GeneOhm MRSA PCR assay showed a relatively high negative predictive value. However, its low specificity and frequent occurrence of unresolved results would be problematic in the endemic areas with a high prevalence of MRSA.

배경 : BD GeneOhm$^{TM}$ MRSA PCR assay (Becton Dickinson, USA)은 메티실린 내성 황색포도알균 비강보균자의 신속한 검출을 위한 정성적 실시간 PCR 검사이다. 저자들은 전비공 도말 검체에서의 MRSA 선별에 GeneOhm MRSA의 수행능을 MRSASelect (Bio-Rad, France) 선별배지와 액체증균배지에 비교하여 평가하였다. 방법 : 2008년 8월에서 2009년 1월 사이에 중환자실에서 의뢰한 295개의 전비공 도말 검체를 대상으로 하였고, 이들은 BD CultureSwab Liquid Stuart Single Swab (Becton Dickinson, USA)으로 채취, 수송되었다. 전비공 도말 검체는 먼저 MRSASelect에 접종 후 GeneOhm 검체완충튜브에 풀었고 현탁액100 $\mu$L을 6.5% NaCl을 첨가한 tryptic soy broth (Becton Dickinson, USA)에 접종하고 하룻밤 배양 후 MRSASelect 선별배지에 계대배양하였다(TSBS). GeneOhm MRSA와 MRSASelect의 수행능을 TSBS에 비교하여 평가하였다. 결과 : GeneOhm MRSA는 125검체(44.6%)가 양성이었고 13검체(4.4%)가 '판독불가', 2검체가 '작동오류'였다. MRSASelect와 TSBS는 각각 86검체(29.4%), 106검체(36.2%)가 양성이었다. GeneOhm MRSA와 MRSASelect의 민감도/특이/양성예측도/음성예측도는 각각 85.8%/77.5%/72.8%/93.5%, 78.3%/98.4%/96.5%/88.9%이었다. 34개의 GeneOhm MRSA 위양성 검체는 33명의 환자에서 얻어졌고, 23명은 직전 또는 직후 감시배양에서 MRSA 양성이었다. 10개의 GeneOhm MRSA 위음성 검체는 모두 이전에 MRSA 또는 메티실린 내성 coagulase negative staphylococci 양성이었으며 항 MRSA 항균제 치료를 받았고 1-4회의 감시배양이 음성이다가 양성으로 전환된 경우였다. 결론 : GeneOhm MRSA는 상대적으로 높은 음성예측도를 보이나 특이도가 낮고'판독불가'결과가 존재하여 MRSA 유병률이 높은 토착화된 장소에서 감시배양을 대치하는데 문제가 될수 있다.

Keywords

• BD GeneOhm;
• MRSA;
• Nasal colonization;
• Performance