Improved sensitivity of a modified polymerase chain reaction amplified DNA probe in comparison with serial tissue culture passage for detection of Chlamydia trachomatis in conjunctival specimens from nepal

Abstract

A sensitive means for detecting ocular chlamydial infections is needed to accurately define the epidemiology of trachoma. Tissue culture is considered the "gold standard," yet it is less than 50% sensitive for ocular specimens. The purpose of this study was to improve the detection rate of culture by serial passage and thereby provide a more reliable basis for comparing polymerase chain reaction (PCR) amplified and 32P DNA probes and direct fluorescent antibody (DFA) tests with culture. Ocular exams on 1043 individuals were scored for trachoma; 252 (24%) had moderate/severe intensity. A total of 1214 conjunctival samples were collected and passaged twice. Of 1053 samples, 276 negative at second passage were passaged an additional two times. The vast majority (93%) of all culture-positive samples were recovered by first passage. Only 80 of 252 cases (32%) with moderate/severe intensity were diagnosed by culture. The sensitivity of the 32P and PCR probes were 87% and 90%, respectively. For DFA versus culture, the sensitivity rate was 48%. Our results indicate that true rates of infection can not be accurately determined by culture even with serial passage. The sensitivity of the probes and DFA tests may, therefore, be higher. The PCR probe holds promise as an epidemiologic tool for studying chlamydial ocular infections.