Evaluation of ELISA to detect Chlamydia trachomatis antigen in urine samples from arthritis patients.

Objective: To determine whether examination of urine samples using ELISA allows the detection of asymptomatic C. trachomatis infection in arthritis patients.

Methods: The in vitro sensitivity of IDEIA Chlamydia ELISA to detect C. trachomatis in urine samples was determined by the investigation of serial dilutions of chlamydial elementary bodies. In a clinical study, urine samples from 402 consecutive arthritis patients (182 men and 220 women) in a tertiary care rheumatology clinic were examined for asymptomatic chlamydial infection by ELISA and the results were compared to culture and direct immunofluorescence assay (DFA, MicroTrak) of urogenital swabs.

Results: The in vitro sensitivity of ELISA for detecting purified elementary bodies of C. trachomatis serovar K in urine was 60 infection forming units. Twenty-three of 402 arthritis patients (6%) had asymptomatic chlamydial infection as shown by DFA and culture from urogenital smears. The ELISA method identified only 3 of 17 swab-positive patients among 271 patients when urine specimens were collected during the clinical visit, while the assay detected all 6 swab-positive patients among 131 patients when first-voided early morning urine specimens were used (p < 0.001).

Conclusion: It is mandatory to examine only first voided early morning urine samples if ELISA is used instead of DFA or culture from urogenital swabs to detect asymptomatic chlamydial infection in arthritis patients.