Surveillance For Peri-Elimination Trachoma Recrudescence: Exploratory Studies In Ghana

Author summaryThe goal for trachoma programmes is elimination of trachoma as a public health problem. This means that ongoing low-level eye-to-eye transmission of the causative bacterium, Chlamydia trachomatis (Ct), is acceptable. Countries need to implement a suitable surveillance system to identify any return to higher transmission levels. The best methodology for doing this is not known. We first explored the approach used by Ghana in its standard programme, which involved monitoring a limited number of randomly selected communities for evidence of active (inflammatory) trachoma visible in children's eyes on examination by trained observers. Although this strategy led to identification of at least one community that had probably had recent Ct transmission, the approach is unlikely to consistently identify places where return to higher levels of transmission is a risk. We also explored using information on infection (detected in eye swabs) and antibodies to Ct (detected in the blood) to identify communities at risk. We found evidence of both persistent eye-to-eye Ct transmission and areas where infection was transient and has now gone away. We conclude that the use of infection and antibody data for surveillance of trachoma appears promising.

IntroductionTo date, eleven countries have been validated as having eliminated trachoma as a public health problem, including Ghana in 2018. Surveillance for recrudescence is needed both pre- and post-validation but evidence-based guidance on appropriate strategies is lacking. We explored two potential surveillance strategies in Ghana.

Methodology/principal findingsAmongst randomly-selected communities enrolled in pre-validation on-going surveillance between 2011 and 2015, eight were identified as having had trachomatous-inflammation follicular (TF) prevalence >= 5% in children aged 1-9 years between 2012 and 2014. These eight were re-visited in 2015 and 2016 and neighbouring communities were also added ("TF trigger" investigations). Resident children aged 1-9 years were then examined for trachoma and had a conjunctival swab to test for Chlamydia trachomatis (Ct) and a dried blood spot (DBS) taken to test for anti-Pgp3 antibodies. These investigations identified at least one community with evidence of probable recent Ct ocular transmission. However, the approach likely lacks sufficient spatio-temporal power to be reliable.

A post-validation surveillance strategy was also evaluated, this reviewed the ocular Ct infection and anti-Pgp3 seroprevalence data from the TF trigger investigations and from the pre-validation surveillance surveys in 2015 and 2016. Three communities identified as having ocular Ct infection >0% and anti-Pgp3 seroprevalence >= 15.0% were identified, and along with three linked communities, were followed-up as part of the surveillance strategy. An additional three communities with a seroprevalence >= 25.0% but no Ct infection were also followed up ("antibody and infection trigger" investigations). DBS were taken from all residents aged >= 1 year and ocular swabs from all children aged 1-9 years. There was evidence of transmission in the group of communities visited in one district (Zabzugu-Tatale). There was no or little evidence of continued transmission in other districts, suggesting previous infection identified was transient or potentially not true ocular Ct infection.

Conclusions/significanceThere is evidence of heterogeneity in Ct transmission dynamics in northern Ghana, even 10 years after wide-scale MDA has stopped. There is added value in monitoring Ct infection and anti-Ct antibodies, using these indicators to interrogate past or present surveillance strategies. This can result in a deeper understanding of transmission dynamics and inform new post-validation surveillance strategies. Opportunities should be explored for integrating PCR and serological-based markers into surveys conducted in trachoma elimination settings.