Estimating the duration of antibody positivity and likely time of Leptospira infection using data from a cross-sectional serological study in Fiji

Abstract

Background Leptospirosis is a zoonotic disease prevalent throughout the world, but with particularly high burden in Oceania (including the Pacific Island Countries and Territories). Leptospirosis is endemic in Fiji, with outbreaks often occurring following heavy rainfall and flooding. As a result of non-specific clinical manifestation and diagnostic challenges, cases are often misdiagnosed or under-ascertained. Furthermore, little is known about the duration of persistence of antibodies to leptospirosis, which has important clinical and epidemiological implications. Methodology and principal findings Using the results from a serosurvey conducted in Fiji in 2013, we fitted serocatalytic models to estimate the duration of antibody positivity and the force of infection (FOI, the rate at which susceptible individuals acquire infection or seroconversion), whilst accounting for seroreversion. Additionally, we estimated the most likely timing of infection. Using the reverse catalytic model, we estimated the duration of antibody persistence to be 8.33 years (4.76–12.50; assuming constant FOI) and 7.25 years (3.36–11.36; assuming time-varying FOI), which is longer than previous estimates. Using population age-structured seroprevalence data alone, we were not able to distinguish between these two models. However, by bringing in additional longitudinal data on antibody kinetics we were able to estimate the most likely time of infection, lending support to the time-varying FOI model. We found that most individuals who were antibody-positive in the 2013 serosurvey were likely to have been infected within the previous two years, and this finding is consistent with surveillance data showing high numbers of cases reported in 2012 and 2013. Conclusions This is the first study to use serocatalytic models to estimate the FOI and seroreversion rate for Leptospira infection. As well as providing an estimate for the duration of antibody positivity, we also present a novel method to estimate the most likely time of infection from seroprevalence data. These approaches can allow for richer, longitudinal information to be inferred from cross-sectional studies, and could be applied to other endemic diseases where antibody waning occurs.

Gender differences in the perception of leptospirosis severity, behaviours, andLeptospiraexposure risk in urban Brazil: a cross-sectional study

“…While it is conventionally characterized that younger adult age groups are at higher risk (12,13), our findings are consistent with previous studies in the city of Salvador that have also identified a linear trend with age (4,15). This may also be partially attributable to the persistence of antibodies, which can remain detectable for several years following exposure and reflects a limitation of this study (53). The persistence of antibodies over several years presents additional challenges as behaviours were self-reported during the previous six months as a measure of exposure risk (53).…”

Quantifying the relationship between climatic indicators and leptospirosis incidence in Fiji: A modelling study

“…This is further compounded, as, to conserve testing capability, once a leptospirosis outbreak has been declared, it is recommended that diagnosis is done based on case definitions and clinical judgement [ 34 ]. Therefore, the cases and the outbreaks reported by the ELISA-positive data are likely to be a small fraction of the true cases occurring in Fiji [ 58 ]. Furthermore, changes in case detection, case reporting and diagnostic capabilities have occurred over time.…”

Seroprevalence, distribution, and risk factors for human leptospirosis in the United States Virgin Islands

“…This association has also been seen in previous Caribbean serosurveys [ 30 , 31 ]. While acute cases tend to occur in young and middle-aged adults most often, anti- Leptospira antibodies can persist for several years, sometimes up to a decade or more [ 33 , 46 ]. Notably, two seropositive participants were children aged five and thirteen years.…”