Clinical application of real-time PCR to screening critically ill and emergency-care surgical patients for methicillin-resistant Staphylococcus aureus: a quantitative analytical study.
The clinical utility of real-time PCR screening assays for methicillin (methicillin)-resistant Staphylococcus aureus (MRSA) colonization is constrained by the predictive values of their results: as MRSA prevalence falls, the assay's positive predictive value (PPV) drops, and a rising proportion of positive PCR assays will not be confirmed by culture. We provide a quantitative analysis of universal PCR screening of critical care and emergency surgical patients using the BD GeneOhm MRSA PCR system, involving 3,294 assays over six months. A total of 248 PCR assays (7.7%) were positive; however, 88 failed to be confirmed by culture, giving a PPV of 65%. Multivariate analysis was performed to compare PCR-positive culture-positive (P+C+) and PCR-positive culture-negative (P+C-) assays. P+C- results were positively associated with a history of methicillin-sensitive Staphylococcus aureus infection or colonization (odds ratio [OR], 3.15; 95% confidence interval [CI], 1.32 to 7.54) and high PCR thresholds of signal intensity, indicative of a low concentration of target DNA (OR, 1.19 per cycle; 95% CI, 1.11 to 1.26). P+C- results were negatively associated with a history of MRSA infection or colonization (OR, 0.19; 95% CI, 0.09 to 0.42) and male sex (OR, 0.40; 95% CI, 0.20 to 0.81). P+C+ patients were significantly more likely to have subsequent positive MRSA culture assays and microbiological evidence of clinical MRSA infection. The risk of subsequent MRSA infection in P+C- patients was not significantly different from that in case-matched PCR-negative controls. We conclude that, given the low PPV and poor correlation between a PCR-positive assay and the clinical outcome, it would be prudent to await culture confirmation before altering infection control measures on the basis of a positive PCR result.
Directorate of Infection, St Thomas' Hospital, Guy's and St Thomas' NHS Foundation Trust, London SE1 7EH, United Kingdom.
M Trent
MT
Herdman
Duncan
D
Wyncoll
Eugene
E
Halligan
Penelope R
PR
Cliff
Gary
G
French
Jonathan D
JD
Edgeworth
D000328:Adult; D001431:Bacteriological Techniques; D002353:Carrier State / Q000175:diagnosis* / Q000382:microbiology; D002648:Child; D002675:Child, Preschool; D016638:Critical Illness; D003470:Culture Media; D004638:Emergency Treatment; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008403:Mass Screening / Q000379:methods*; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification*; D015999:Multivariate Analysis; D009296:Nasal Cavity / Q000382:microbiology*; D016133:Polymerase Chain Reaction / Q000379:methods*; D011237:Predictive Value of Tests; D013203:Staphylococcal Infections / Q000175:diagnosis / Q000382:microbiology; D013514:Surgical Procedures, Operative
D003470:Culture Media