Effect of blind passage and multiple sampling on recovery of Chlamydia trachomatis from urogenital specimens

Detection of Chlamydia trachomatis by enzyme immunoassay in patients with trachoma

Trachoma control necessitates identification of individuals shedding ocular chlamydiae. Conventional techniques of chlamydial culture are unsuitable for large field surveys in developing countries. In this study an enzyme immunoassay (EIA) developed for the detection of chlamydial antigen in genital-tract infection was used in trachoma. Conjunctival swabs were taken for chlamydial antigen detection from 1225 subjects in a Gambian village with endemic trachoma. Of these, 997 had insignificant or no disease and 172 had mild, 30 moderate, and 26 severe disease. Chlamydial antigen was detected in 5.0%, 20.3%, 46.7%, and 26.9% of subjects in these four categories, respectively. Samples for chlamydial isolation were obtained from 259 subjects. The corresponding rates of detection obtained by chlamydial isolation were 3/90 (3.3%), 16/129 (12.4%), 7/21 (33.3%), and 7/19 (36.8%). If isolation is taken as the "gold standard", the EIA technique had a sensitivity of 70.6% and a specificity of 90%. A substantial proportion of subjects with severe conjunctival scarring, from whom chlamydiae cannot generally be isolated, were antigen positive by EIA, implying that persistent chlamydial antigen plays a part in the pathogenesis of the late sequelae of trachoma.

Failure of multiple passages to increase chlamydial recovery

Because of a previous publication indicating that increasing the number of blind passages to five resulted in a marked increase in Chlamydia trachomatis isolation rates, we evaluated a multiple-blind-passage system in vials. Cervical specimens from 119 pregnant women and 82 specimens from other sources were tested for chlamydial infection. The recovery rate for C. trachomatis was not markedly increased after the first blind passage. Thus, we conclude that multiple blind passages are not necessary to maximize the C. trachomatis isolation rate in a vial system.

Diagnosis of chlamydial infection in women attending antenatal and gynecologic clinics

Two antigen detection systems (MicroTrak [MT], Syva Co., Palo Alto, Calif.; and Chlamydiazyme [CZ], Abbott Laboratories, North Chicago, Ill.) were compared with semiquantitative culture for diagnosis of chlamydial infection in 1,059 patients. Cultures were done on microtiter plates and blind passaged once. Culture-negative but CZ- or MT-positive specimens were recultured. True positives were positive by either initial or repeat cultures. Of 827 nonpregnant and 231 pregnant patients, 9.1 and 12.1%, respectively, had positive cultures. Overall sensitivity of the initial culture was 48.5% without passage and 86.4% with passage. The sensitivity of CZ was 67%. The sensitivity of MT in our laboratory was 50%; however, further review of these specimens by Syva employees gave a combined sensitivity of 71.6%. MT and CZ were more sensitive for pregnant patients (MT, 84.6%; CZ, 85.7%) than for nonpregnant patients (MT, 65.5%; CZ, 60.0%). All the tests had specificities above 95%. Of the specimens that were positive after initial culture without subculture, MT-negative specimens had a mean of 3.7 inclusions in culture, and MT-positive specimens had a mean of 24.8 (P = 0.002); CZ-negative specimens had a mean of 4.3 inclusions, and CZ-positive specimens had a mean of 20.0 (P = 0.026). In addition, cultures of specimens from pregnant patients had more inclusions than did those from gynecology patients, but this was not statistically significant (P = 0.096). No method is ideal; however, MT and CZ were less sensitive than was this culture system for detecting chlamydial infection in patients in gynecology clinics and were of comparable sensitivity for pregnant patients.