False positive results with the use of chlamydial antigen detection tests in the evaluation of suspected sexual abuse in children.

The presence of rectal or genital infection with Chlamydia trachomatis in children is frequently considered an indicator of sexual abuse. The diagnosis of chlamydial infection in these children has been complicated by the use of antigen detection methods instead of culture. We report five cases in which the use of chlamydial antigen detection tests in the evaluation of suspected child abuse gave false positive results. An enzyme immunoassay was used in two cases (Chlamydiazyme; Abbott Diagnostics) and a direct fluorescent antibody test was used in the remaining three cases (Microtrak; Syva). The sites examined were the urethra, vagina and rectum. In all cases chlamydial cultures obtained several days later with no interim antibiotic therapy were negative. Four of the five children examined were probably victims of sexual abuse. The enzyme immunoassay and direct fluorescent antibody tests have been evaluated primarily for urethral and cervical cultures from adults; neither test has been approved or evaluated for rectal or genital sites in children. At these sites use of both tests may be associated with a large proportion of false positives caused by contamination with fecal flora which can cross-react with the antibodies used in the test. These tests also have limited utility in populations where the prevalence of chlamydial infection is low (less than 10%), as has been reported for sexually abused children. Because of the medicolegal implications only "gold standard" methods (i.e. culture) performed by a competent laboratory should be used in evaluating chlamydial infection in sexually abused children.