INTERPRETATION OF CHLAMYDIA-TRACHOMATIS ANTIBODY-RESPONSE IN CHLAMYDIAL OCULOGENITAL INFECTION

Objective-To study: (a) the chlamydial antibody response (to the D-K s erovars) using the micro-immunofluorescence (micro-IF) test in the fol lowing groups: (I) chlamydial genital infection only, (II) chlamydial ocular infection only, (III) combined chlamydial ocular and genital in fection (oculo-genital infection), (IV) chlamydial ocular infection wi th chlamydia-negative non-gonococcal urethritis, (V) adenovirus conjun ctivitis (control group 1), (VI) male partners of group I-IV with no c hlamydial oculogenital infection or non-gonococcal urethritis (control group 2) (b) the cross reactivity of antibodies in patients' sera bet ween the three chlamydial species and within the serovars of C trachom atis in those with culture-positive chlamydial oculogenital infection. Setting-oculogenital (diagnostic) clinic at Moorfields Eye Hospital, London, UK. Subjects-209 consecutive patients attending the clinic wit h Chlamydia trachomatis oculogenital infection and 86 patients with ad enovirus conjunctivitis (control group 1) and 55 male partners with no evidence of chlamydial oculogenital infection or non-gonococcal ureth ritis (control group 2). Results-Of all the patients with proven chlam ydial oculogenital infection, 10.5% (22/209) and 94% (197/209) had IgM and IgG antibodies respectively. The geometric mean IgG antibody titr es (GAIT) were 1:98, 1:123, 1:245 and 1:101 in groups I to IV respecti vely. The IgG GAIT values seen in control groups 1 and 2 were 1:45 and 1:36 respectively. Only 2/86(2%) patients in group V (control group 1 ) had IgG chlamydial antibodies of 1:32 and 1:64, whilst only 1/55(1.8 %) and 4/55(7.3%) of patients in group VI(control group 2) had chlamyd ial IgG antibody titres of greater than or equal to 1:256 and greater than or equal to 1:128 respectively. A four-fold rise or fall in IgG a ntibody titre occurred in 56%(107/192) of patient groups I-IV over 2-6 weeks. Low titre cross-reactive antibody responses against different chlamydial species and serovars were commonly seen; 71%(148/209) of al l patients showed cross-reactivity with Chlamydia pneumoniae or psitta ci species or both, whilst 92% (193/209) of patients showed some level of crossreactivity to other pooled serovars of C trachomatis (A-C and L 1-3). Conclusions-Serological diagnosis of chlamydial infection as evidenced by a positive IgM antibody response, high IgG titre (greater than or equal to 1:256) or greater than or equal to 4-fold rise or fa ll in IgG antibody titre was seen in 78%(163/209) of patients with cul ture-positive chlamydial oculogenital infection. Chlamydial IgG antibo dy titres of greater than or equal to 1:256 had a sensitivity of 42.6% , specificity of 98.2%, positive predictive value of 98.8% and a negat ive predictive value of 31% for chlamydial infection at any site, when considering groups I-IV and control group 2. In this study of 216 pat ients with conjunctivitis, a positive IgG antibody response (titre gre ater than or equal to 1:16) had a sensitivity of 98.5%, specificity of 97.7%, positive predictive value of 98.5% and a negative predictive v alue of 97.7%, for chlamydial conjunctivitis. Patients with dual chlam ydial infection of conjunctiva and genital tract had a higher IgG GAIT titre than those with ocular or genital infection alone: infection at a second site may produce an anamnestic response. Although the micro- IF test is a useful adjunct for the diagnosis of chlamydial infection, cross-reactivity between different chlamydial species and serovars is common. Chlamydial seroepidemiological studies should be interpreted with caution, as studies may attribute a serological response to a par ticular species or serovar in a setting where two or more are prevalen t.