OBJECTIVETo detect the RNA of severe acute respiratory syndrome virus (SARS-CoV) by using reverse transcription polymerase chain reaction (RT-PCR) targeted for a two loci and a modified nested real-time RT-PCR as to improving the reliability and sensitivity of tests.

METHODSA nested RT-PCR was used for detecting one fragment of SARS-CoV RNA in oropharyngeal swabs from 3 SARS probable patients, 4 SARS suspect patients and other 27 patients with fever in Hangzhou, and the nested RT-PCR product from one SARS probable patient was sequenced. Meanwhile in these 3 SARS probable patients, other three RT-PCR methods, including a hemi-nested RT-PCR targeted for another fragment of SARS-CoV RNA, a real-time RT-PCR and a modified nested real-time RT-PCR, were employed to detect SARS-CoV RNA.

RESULTSTwo positives were found in the 3 SARS probable patients, and none positive in 4 SARS suspect patients and other 27 patients with fever, using the nested RT-PCR. The sequence of the nested RT-PCR product from one SARS probable patient was identified with the counterpart of SARS-CoV genomes published in public database. The results of the hemi-nested RT-PCR, the real-time RT-PCR and the modified nested real-time RT-PCR in the 3 SARS patients were consistent with the one of the nested RT-PCR. During detecting specimen with low copies of RNA, a weak positive signal was produced after about 35 cycles in the real-time RT-PCR, but a strong positive signal was found only after 10 cycles in the modified nested real-time RT-PCR.

CONCLUSIONIt might improve the reliability of test by employing RT-PCR targeted for two or more fragments in SARS-CoV genome. The modified nested real-time RT-PCR might have higher sensitivity than the routine real-time RT-PCR.