The use of serological titres of IgA and IgG in (early) discrimination between rectal infection with non-lymphogranuloma venereum and lymphogranuloma venereum serovars of Chlamydia trachomatis.

Objectives: To investigate whether serological titres of species-specific IgA and IgG antibodies in patients with rectal chlamydial infection could discriminate between infection with serovar L2 lymphogranuloma venereum (LGV) and infection with non-LGV serovars.

Methods: A total of 39 male patients with chlamydial infection of the rectum were tested for titres of IgA and IgG antibodies within 14 days after detection of the infection and 6 and 12 months after adequate treatment. Data were collected regarding demographics, sexual orientation, HIV serostatus, history of chlamydial infection, concomitant sexually transmitted infection (STI) or HIV infection, hepatitis C virus antibodies and new STIs during follow-up.

Results: Between May 2003 and November 2005, 24 men with confirmed L2 proctitis and 15 men with non-LGV rectal chlamydial infection were recruited. In multivariable analyses, both high titre of IgA within 14 days after detection of the infection and older age of the individual were found significantly associated with L2 proctitis (p<0.001 and p = 0.001, respectively). A total sum score of seven times IgA titre and individual's age >or=50 years resulted in an overall sensitivity of 92% and specificity of 100%. This total sum score was highly accurate for detection of LGV proctitis, with an area under the curve in a receiver operating characteristic curve of 0.989.

Conclusions: An increased IgA antibody response and the age of the infected individual are of possible diagnostic value for (early) detection of LGV proctitis.