Abstract
Background: The low population-prevalence of trachomatous trichiasis and high prevalence of trachomatous inflammation-follicular (TF) provide contradictory estimates of the magnitude of the public health threat from trachoma in the Solomon Islands. Improved characterisation of the biology of trachoma in the region may support policy makers as they decide what interventions are required. Here, age-specific profiles of anti-Pgp3 antibodies and conjunctival scarring were examined to determine whether there is evidence of ongoing transmission and pathology from ocular Chlamydia trachomatis (Ct) infection. Methods: A total of 1511 individuals aged ≥1 year were enrolled from randomly selected households in 13 villages in which >10% of children aged 1-9 years had TF prior to a single round of azithromycin mass drug administration undertaken six months previously. Blood was collected to be screened for antibodies to the Ct antigen Pgp3. Tarsal conjunctival photographs were collected for analysis of scarring severity. Results: Anti-Pgp3 seropositivitywas 18% in 1-9 year olds, sharply increasing around the age of sexual debut to reach 69% in those over 25 years. Anti-Pgp3 seropositivity did not increase significantly between the ages of 1-9 years and was not associated with TF (p=0.581) or scarring in children (p=0.472).Conjunctival scars were visible in 13.1% of photographs. Mild (p<0.0001) but not severe (p=0.149) scars increased in prevalence with age. Conclusions: Neither conjunctival scars nor lymphoid follicles were associated with antibodies to Ct, suggesting that they are unlikely to be a direct result of ocular Ct infection . Clinical signs of trachoma were prevalent in this population but were not indicative of the underlying rates of Ct infection. The current World Health Organization guidelines for trachoma elimination indicated that this population should receive intervention with mass distribution of antibiotics, but the data presented here suggest that this may not have been appropriate.
Highlights
Trachoma is responsible for approximately 1.9 million cases of visual impairment or blindness globally1
The reviewers main suggestions were to improve transparency around training and validation of clinical and photograph graders and acknowledge limitations in that process. We feel these were valuable suggestions which would improve the manuscript and have added three new sections to the manuscript: [1] In the Methods section, more detail has been added to the information on Trachoma Grading, both for clinical graders and photograph graders; [2] In the Results section, we have presented the outcome of the comparison between the photograph grade and the field grade and have clarified how many photographs had to be adjudicated; and [3] In the Discussion section, we have added a paragraph on the limitations of photograph and field grading, the potential for disagreement and the implications of that on our data
International partners have committed to elimination of trachoma as a public health problem by the year 2020 and the global elimination strategy is guided by the clinical signs trachomatous trichiasis (TT) and trachomatous inflammation–follicular (TF)
Summary
Trachoma is responsible for approximately 1.9 million cases of visual impairment or blindness globally. A 2013 population-based prevalence survey (PBPS) covering two provinces (Temotu and Rennell & Bellona) of the Solomon Islands showed that the proportion of 1–9-year-old children with TF was moderately high (26.1%). Scarring, caused by immuno-pathological responses to repeated cycles of infection, is an irreversible process that, like Ct seropositivity, is generally considered to be a persistent marker of previous ocular Ct infection. In trachoma, it is characterised by a gradual accumulation of scar tissue in the tarsal conjunctivae, which typically begins to develop to the point of being visible in late childhood. Assuming that trachoma was an endemic problem in this population, we would expect to observe an age-dependent accumulation of scarring, with an increasing proportional representation of severe scars with advancing age
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