[Detection of leptospiral DNA in the serum of 175 patients with early leptospirosis by polymerase chain reaction].

We have developed a sensitive assay for leptospira, using the polymerase chain reaction (PCR). On the basis of the published nucleotides sequence of 23S rRNA gene from Leptospira interrogans serovar canicola strain Moulton, primers were chosen to produce an amplified fragment of 123 bp. Primer A: 5'GAT CTA ATT CGC TGT AGC AGG3' and primer B: 5'ACT TTC ACC CTC TAT GGT CGG3' Eight different svs. of Leptospira interrogans could all be detected by PCR, but the DNAs from L. biflexa. Leptonema bacteria, virus and human could not produce the specific amplified fragment. The assay detected approximately 10 fg of purified leptospiral DNA and 1 microliter serum of experimental animal. Positive results were obtained from simulated positive samples containing a single organism leptospiral DNA. The diagnostic test (proved by "gold standards": Clinical diagnosis; blood culture and MAT) showed that the sensitivity was 92.00%; the specificity 94.35%; the accuracy 92.54%; the positive predictive value 98.17%; the negative predictive value 78.13%; the positive likelihood ratio 16.25; and the negative likelihood ratio 0.0848. The diagnosis of early leptospirosis by using PCR may become a significant addition to diagnostic means.