Serology for Trachoma Surveillance after Cessation of Mass Drug Administration

Abstract

BackgroundTrachoma, caused by Chlamydia trachomatis (Ct), is the leading infectious cause of blindness worldwide. Yearly azithromycin mass drug administration (MDA) plays a central role in efforts to eliminate blinding trachoma as a public health problem. Programmatic decision-making is currently based on the prevalence of the clinical sign “trachomatous inflammation-follicular” (TF) in children. We sought to test alternative tools for trachoma surveillance based on serology in the 12-year cohort of Kahe Mpya, Rombo District, Tanzania, where ocular chlamydial infection was eliminated with azithromycin MDA by 2005.Methodology and Principal FindingsThe present study was a community-based cross-sectional survey in Kahe Mpya. Of 989 residents, 571 people aged 6 months to 87 years were enrolled: 58% of the total population and 73% of 1–9 year olds, the key WHO indicator age group. Participants were examined for TF, had conjunctival swabs collected for nucleic acid amplification test (NAAT)-based detection of Ct, and blood collected for analysis of antibodies to the Ct antigens pgp3 and CT694 by multiplex bead-based immunoassay. Seroconversion rate was used to estimate changes in the force of infection in a reversible catalytic model. No conjunctival swabs tested positive for Ct infection by NAAT. Among 1–9 year olds, TF prevalence was 6.5%, whereas only 3.5% were seropositive. Force of infection modelling indicated a 10-fold decrease in seroconversion rate at a time corresponding to MDA commencement. Without baseline serological data, the inferences we can make about antibody status before MDA and the longevity of the antibody response are limited, though our use of catalytic modelling overcomes some of these limitations.Conclusions/SignificanceSerologic tests support NAAT findings of very low to zero prevalence of ocular Ct in this community and have potential to provide objective measures of transmission and useful surveillance tools for trachoma elimination programs.

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

“…We might expect those with TF in the absence of Ct to be at lower risk of progression to TS and TT than those with repeated Ct infection and inflammation (40), however, such individuals have not been studied longitudinally to assess outcomes therefore it is unclear how these cases should be managed. Furthermore, years after MDA has been administered, TF persists at levels above the threshold for elimination (>5%) in communities where Ct infection is not readily detectable (41, 42). The public health risk of trachoma in these communities is also unclear.…”

Community seroprevalence survey for yaws and trachoma in the Western Division of Fiji

“…21 Steeply increasing age-specific anti-pgp3 prevalence in children aged between 1 and 10 years is thought to be indicative of intense transmission of ocular C. trachomatis ; in this population the prevalence of anti-pgp3 antibodies was already high in the 1-year age group, suggesting the majority of seropositivity was acquired at in the first year of life. 12,21 As Pgp3 is conserved between urogenital and ocular strains of C. trachomatis we cannot discount the possibility that the Pgp3 seroprevalence may reflect transmission in the birth canal as well as, or indeed more than, ocular transmission of chlamydia. The prevalence of urogenital C. trachomatis infection amongst pregnant women has previously been reported to be high in Fiji and community prevalence surveys in other Pacific countries have also reported high rates of urogenital C. trachomatis .…”

“…For trachoma, antibodies to Pgp3 are thought to be a long-lived and specific marker for prior C. trachomatis exposure. 11,12 Serology is also a major tool in surveillance for yaws. Treponemal antibodies persist for life and cannot distinguish between yaws and syphilis.…”

Serology reflects a decline in the prevalence of trachoma in two regions of The Gambia

“…Situations such as this highlight the need to develop new tools that can support programmes to make informed decisions about how to use antimicrobials in trachoma control. Antibodies against Chlamydia trachomatis reflect cumulative exposure to Ct 10 , 11 and it has been suggested that programmes could use some measure of seroprevalence as an alternative indicator of changes in transmission 12 , 13 . Previous work has investigated the use of age-specific seroprevalence for surveillance in the peri- 14 and post-MDA setting 13 , 15 , 16 .…”

“…Antibodies against Chlamydia trachomatis reflect cumulative exposure to Ct 10 , 11 and it has been suggested that programmes could use some measure of seroprevalence as an alternative indicator of changes in transmission 12 , 13 . Previous work has investigated the use of age-specific seroprevalence for surveillance in the peri- 14 and post-MDA setting 13 , 15 , 16 . Serological techniques for the detection of antibodies against Ct have been used to study the epidemiology of both urogenital and ocular Ct infections 17 , 18 .…”