Comparison of two culture approaches, blind passage and dual observation, for detecting Chlamydia trachomatis in various prevalence populations

Chlamydia trachomatis diagnosis in our laboratory consisted of dual inoculation of shell vials and detection of inclusions by using fluorescein- conjugated monoclonal antiserum; the second culture vial was conventionally used for blind passage when the first vial was negative. We compared the increase in positivity using blind passage with that of a strategy utilizing observation of two stained monolayers (dual observation) without blind passage, in an effort to reduce the reporting time and labor associated with the conventional approach. A total of 4,329 specimens were obtained from an obstetrics and gynecology (OB-GYN) clinic (2,563 specimens) and the sexually transmitted disease clinic (1,766 specimens). These specimens were used to compare the two strategies. Blind passage of 1,269 initially culture-negative specimens from the OB-GYN clinic resulted in an additional 6 positive chlamydial diagnoses. In comparison, a similar number of specimens (1,294) from the OB-GYN clinic collected subsequently to the first group were tested by dual observation. There were five additional positive findings. A similar evaluation of specimens from the sexually transmitted disease clinic was performed. Blind passage of 313 initially culture-negative specimens yielded 3 additional positive diagnoses, whereas dual observation of 1,435 similar specimens resulted in 9 positive diagnoses. On the basis of analysis of 4,332 specimens, sensitivity of dual observation is comparable to that of blind passage; labor, cost, and reporting time of dual observation are reduced in comparison to those of blind passage.