Diagnosis of bubonic plague by PCR in Madagascar under field conditions

The diagnostic value of a PCR assay that amplifies a 501-bp fragment of the Yersinia pestis caf1 gene has been determined in a reference laboratory wi th 218 bubo aspirates collected from patients with clinically suspected pla gue managed in a regional hospital in Madagascar, The culture of Y. pestis and the detection of the F1 antigen (Ag) by enzyme-linked immunosorbent ass ay (ELISA) were used as reference diagnostic methods. The sensitivity of PC R nas 89% (57 of 64) for the Y. pestis-positive patients, and 80.7% (63 of 78) for the F1 Ag-positive patients. The specificity of PCR for the culture -, F1 Ag-, and antibody-negative patients (n = 105) was 100%. Because in Ma dagascar most patients with plague are managed and their clinical samples a re collected in remote villages, the usefulness of PCR was evaluated for ro utine diagnostic use in the operational conditions of the control program. The sensitivity of PCR nas 50% (25 of 50) relative to the results of cultur e and 35.2% (19 of 54) relative to the results of the F1 Ag immunocapture E LISA. The specificity of PCR under these conditions was 96%. In conclusion, the PCR method was found to be very specific but not as sensitive as cultu re or the F1 Ag detection method. The limitation in sensitivity may have be en due to suboptimal field conditions and the small volumes of samples used for DNA extraction. This technique is not recommended as a routine diagnos tic test for plague in Madagascar.