Detecting extra-ocular Chlamydia trachomatis in a trachoma-endemic community in Ethiopia: Identifying potential routes of transmission

Background: Trachoma elimination efforts are hampered by limited understanding of Chlamydia trachomatis (Ct) transmission routes. Here we aimed to detect Ct DNA at non-ocular sites and on eye-seeking flies. Methods: A population-based household survey was conducted in Oromia Region, Ethiopia. Ocular and non-ocular (faces, hands, clothing, water containers and sleeping surfaces) swabs were collected from all individuals. Flies were caught from faces of children. Flies, ocular swabs and non-ocular swabs were tested for Ct by quantitative PCR. Results: In total, 1220 individuals in 247 households were assessed. Active trachoma (trachomatous inflammation—follicular) and ocular Ct were detected in 10% and 2% of all-ages, and 21% and 3% of 1–9-year-olds, respectively. Ct was detected in 12% (95% CI:8–15%) of tested non-ocular swabs from ocular-positive households, but in none of the non-ocular swabs from ocular-negative households. Ct was detected on 24% (95% CI:18–32%) of flies from ocular-positive households and 3% (95% CI:1–6%) of flies from ocular-negative households. Conclusion: Ct DNA was detected on hands, faces and clothing of individuals living in ocular-positive households suggesting that this might be a route of transmission within Ct infected households. In addition, we detected Ct on flies from ocular-positive households and occasionally in ocular-negative households suggesting that flies might be a vector for transmission within and between Ct infected and uninfected households. These potential transmission routes may need to be simultaneously addressed to suppress transmission. Author summary: Trachoma elimination efforts are hampered by limited understanding of Ct transmission routes. One previous study demonstrated Ct in nasal secretions, with lower loads than in paired ocular samples. Two other studies reported 15–23% of Musca sorbens caught leaving the faces of Ethiopian children to be PCR-positive for Ct in untreated villages with 30–50% TF prevalence. To date, no published studies have systematically documented the relative frequency of Ct by PCR on non-ocular surfaces and flies. Cross-sectional studies consistently find active trachoma and ocular Ct infection associated with factors such as dirty faces, fly-eye contact, limited water access, crowded living conditions and limited sanitation. In this study, we conducted a population-based household survey in Oromia Region, Ethiopia and test the hypothesis that Ct can be detected at multiple non-ocular sites and on eye-seeking flies. The results of our study show that Ct DNA was only detected on hands, faces and clothing of individuals living in ocular-positive households. In addition, Ct-positive flies were much more likely to be found in ocular-positive households. These findings suggest there may be several plausible ocular Ct transmission routes between people, within and between households, which would need to be simultaneously addressed within communities to suppress transmission.