Low Prevalence of Conjunctival Infection with Chlamydia trachomatis in a Treatment-Naïve Trachoma-Endemic Region of the Solomon Islands

Abstract

BackgroundTrachoma is endemic in several Pacific Island states. Recent surveys across the Solomon Islands indicated that whilst trachomatous inflammation—follicular (TF) was present at levels warranting intervention, the prevalence of trachomatous trichiasis (TT) was low. We set out to determine the relationship between chlamydial infection and trachoma in this population.MethodsWe conducted a population-based trachoma prevalence survey of 3674 individuals from two Solomon Islands provinces. Participants were examined for clinical signs of trachoma. Conjunctival swabs were collected from all children aged 1–9 years. We tested swabs for Chlamydia trachomatis (Ct) DNA using droplet digital PCR. Chlamydial DNA from positive swabs was enriched and sequenced for use in phylogenetic analysis.ResultsWe observed a moderate prevalence of TF in children aged 1–9 years (n = 296/1135, 26.1%) but low prevalence of trachomatous inflammation—intense (TI) (n = 2/1135, 0.2%) and current Ct infection (n = 13/1002, 1.3%) in children aged 1–9 years, and TT in those aged 15+ years (n = 2/2061, 0.1%). Ten of 13 (76.9%) cases of infection were in persons with TF or TI (p = 0.0005). Sequence analysis of the Ct-positive samples yielded 5/13 (38%) complete (>95% coverage of reference) genome sequences, and 8/13 complete plasmid sequences. Complete sequences all aligned most closely to ocular serovar reference strains.DiscussionThe low prevalence of TT, TI and Ct infection that we observed are incongruent with the high proportion of children exhibiting signs of TF. TF is present at levels that apparently warrant intervention, but the scarcity of other signs of trachoma indicates the phenotype is mild and may not pose a significant public health threat. Our data suggest that, whilst conjunctival Ct infection appears to be present in the region, it is present at levels that are unlikely to be the dominant driving force for TF in the population. This could be one reason for the low prevalence of TT observed during the study.

Clinical signs of trachoma are prevalent among Solomon Islanders who have no persistent markers of prior infection with Chlamydia trachomatis

“…This is concordant with our previous data, which suggested that although ocular Ct strains are present in the Solomon Islands, they are rare 3 . This contrasts with the data from Kiritimati Island, where we saw that there was a substantial year-on-year increase in age specific seropositivity ( Figure 3B).…”

“…Whilst measures for trachoma elimination have already been deployed in Temotu and Rennell & Bellona, we have previously noted that TI, ocular Ct infection and late-stage disease (TT) are rare 3 . If the village level findings of the current study were replicated throughout the district, then TF would still be sufficiently prevalent to warrant continued intervention.…”

Active trachoma cases in the Solomon Islands have varied polymicrobial community structures but do not associate with individual non-chlamydial pathogens of the eye

“…In the Solomon Islands, the prevalence of TF is sufficient to warrant MDA but the prevalence of trachomatous trichiasis (TT) suggests trachoma may not pose a significant public health problem. A recent trachoma survey in a treatment-naïve population of the Solomon Islands estimated 26% of 19-year-olds to have TF but, surprisingly, conjunctival Ct infection was detected in only 1.3% of that age group (3). Whilst Ct infection is not always detectable in TF cases (4, 5), infection prevalence in the Solomon Islands is far lower than is seen in other countries with similar TF prevalence (3).…”

Survey, Culture, and Genome Analysis of Ocular Chlamydia trachomatis in Tibetan Boarding Primary Schools in Qinghai Province, China

“…All these reports have no description of intense inflammatory trachoma or more severe trachoma cases, likely due to the low prevalence of trachoma in these areas. Given that presence of clinical signs of trachoma such as conjunctival follicles might be due to non-chlamydial causes in low prevalence settings or regions (Butcher et al, 2016), the use of a specific nucleic acid amplification test or preferably whole-genome sequencing is recommended in order to establish or rule out the cause of disease.…”