Not again! Effect of previous test results, age group and reason for testing on (re-)infection with Chlamydia...

Infection with Chlamydia trachomatis (Ct) is the most commonly reported sexually transmitted infection in Europe. In Germany, Ct screening is offered free of charge to pregnant women since 1995 and to women < 25 years of age since 2008. For symptomatic individuals, testing is covered by statutory health insurance. Study results have shown that repeat Ct infection occurs in 10-20% of previously infected women and men. Our aim was to describe persons tested for Ct and to investigate the determinants of (repeat) Ct infection in women and men in Germany.

We analysed Ct test results from men and women tested between 2008 and 2014 in laboratories participating in the German Chlamydia trachomatis Laboratory Sentinel surveillance. Reinfection was defined as at least 2 positive laboratory tests within more than 30 days. We performed logistic regression stratified by sex and, for women, reason for testing to determine the effect of previous test results and age group on subsequent test results.

In total, 2,574,635 Ct tests could be attributed to 1,815,494 women and 123,033 men. 5% of women and 14% of men tested positive at least once. 15-19- and 20-24-year-old women tested positive at least once respectively in 6.8 and 6.0%, while men respectively in 16.6 and 21.2%. Altogether, 23.1% of tested women and 11.9% of tested men were tested repeatedly between 2008 and 2014. Among those who previously tested positive, reinfection occurred in 2.0% of women and 6.6% of men. Likelihood to be tested Ct positive was higher in women and men with a positive Ct test in the past compared to previously tested Ct negative, odds ratios 4.7 and 2.6 (p < 0.01) respectively. Odds ratios ranged by age group and test reason.

A history of Ct infection increased the likelihood of infection with Ct in women and men taking into account the result of the previous test. Health education, safer sex and treatment of partners are necessary for women and men who have tested positive to prevent reinfection and complications and to interrupt the chain of transmission. To identify potential reinfection repeat testing after treatment should be performed.