Concordance of ompA types in children re-infected with ocular Chlamydia trachomatis following mass azithromycin treatment for trachoma.

Background: The chlamydial major outer membrane protein, encoded by the ompA gene, is a primary target for chlamydial vaccine research. However, human studies of ompA-specific immunity are limited, and prior studies have been limited in differentiating re-infection from persistent infection. The purpose of this study was to assess whether children living in trachoma-endemic communities with re-infections of ocular chlamydia were more likely to be infected with a different or similar genovar. Methodology and findings: The study included 21 communities from a trachoma-hyperendemic area of Ethiopia that had been treated with a mass azithromycin distribution for trachoma. Conjunctival swabbing was offered to all children younger than 5 years of age at baseline (i.e., pre-treatment), and then at follow-up visits 2 and 6 months later. Swabs were subjected to polymerase chain reaction (PCR) to detect C. trachomatis. A random sample of 359 PCR-positive swabs, stratified by study visit and study community, was chosen for ompA sequencing. In addition, ompA sequencing was performed on all swabs of 24 children who experienced chlamydial re-infection (i.e., positive chlamydial test before treatment, negative test 2 months following mass distribution of azithromycin, and again a positive test 6 months post-treatment). ompA sequencing was successful for 351 of 359 swabs of the random sample and 44 of 48 swabs of the re-infection sample. In the random sample, ompA types clustered within households more than would be expected by chance. Among the 21 re-infected children with complete ompA data, 14 had the same ompA type before and after treatment. Conclusion: The high frequency of ompA concordance suggests incomplete genovar-specific protective immunity and the need for multiple antigens as vaccine targets. Author summary: Trachoma is the world's leading infectious cause of blindness. Periodic mass azithromycin distributions have not resulted in elimination. Re-infection is thought to be an important barrier to elimination, but studies of serovar- or genovar-specific immunity and re-infection with ocular Chlamydia trachomatis have been limited. The present study investigated chlamydial genotypes in children who were infected with ocular chlamydia before azithromycin treatment and were confirmed to have cleared the infection 2 months later, but then were again infected at 6 months. The majority of re-infections were caused by the same ompA strain that was carried pre-treatment, which suggests poor protective immunity to chlamydia. The ompA types clustered by household, suggesting members of the same household as a source of re-infection. These findings could inform future mass treatment strategies and vaccine development. [ABSTRACT FROM AUTHOR]