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What could re-infection tell us about R0? A modeling case-study of syphilis transmission.

ABSTRACT: Many infectious diseases can lead to re-infection. We examined the relationship between the prevalence of repeat infection and the basic reproductive number (R0). First we solved a generic, deterministic compartmental model of re-infection to derive an analytic solution for the relationship. We then numerically solved a disease-specific model of syphilis transmission that explicitly tracked re-infection. We derived a generic expression that reflects a non-linear and monotonically increasing relationship between proportion re-infection and R0 and which is attenuated by entry/exit rates and recovery (i.e. treatment). Numerical simulations from the syphilis model aligned with the analytic relationship. Re-infection proportions could be used to understand how far regions are from epidemic control, and should be included as a routine indicator in infectious disease surveillance.

SUBMITTER: Feldman J

PROVIDER: S-EPMC6806446 | biostudies-literature | 2019

REPOSITORIES: biostudies-literature

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What could re-infection tell us about R<sub>0</sub>? A modeling case-study of syphilis transmission.

Feldman Joshua J Mishra Sharmistha S

Infectious Disease Modelling 20190917

Many infectious diseases can lead to re-infection. We examined the relationship between the prevalence of repeat infection and the basic reproductive number (R<sub>0</sub>). First we solved a generic, deterministic compartmental model of re-infection to derive an analytic solution for the relationship. We then numerically solved a disease-specific model of syphilis transmission that explicitly tracked re-infection. We derived a generic expression that reflects a non-linear and monotonically incr ...[more]

PMID: 31667445

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Project description:BackgroundCanadian Arctic communities have experienced sustained syphilis transmission, with diagnoses rates 18-times higher than the national average. Remoteness from laboratory facilities leads to delays between syphilis screening and treatment, contributing to onward transmission. Rapid diagnostic tests can eliminate treatment delays via testing at the point-of-care. This study aims to describe syphilis diagnostic gaps and to estimate the impact of introducing rapid diagnostic tests at the point-of-care on syphilis transmission.MethodsTo assess the population-level impact of deploying rapid diagnostic tests, an individual-based model was developed using detailed surveillance data, population surveys, and a prospective diagnostic accuracy field study. The model was calibrated to syphilis diagnoses (2017-2022) from a community of approximately 1,050 sexually active individuals. The impacts of implementing rapid diagnostic tests using whole blood (sensitivity: 92% for infectious and 81% for non-infectious syphilis; specificity: 99%) from 2023 onward was calculated using the annual median fraction of cumulative new syphilis infections averted over 2023-2032.FindingsThe median modeled syphilis incidence among sexually active individuals was 44 per 1,000 in 2023. Males aged 16-30 years exhibited a 51% lower testing rate than that of their female counterparts. Maintaining all interventions constant at their 2022 levels, implementing rapid diagnostic tests could avert a cumulative 33% (90% credible intervals: 18-43%) and 37% (21-46%) of new syphilis infections over 5 and 10 years, respectively. Increasing testing rates and contact tracing may enhance the effect of rapid diagnostic tests.InterpretationImplementing rapid diagnostic tests for syphilis in Arctic communities could reduce infections and enhance control of epidemics. Such effective diagnostic tools could enable rapid outbreak responses by providing same-day testing and treatment at the point-of-care.FundingCanadian Institutes of Health Research.

Project description:BACKGROUND:In Uruguay it is mandatory to review all cases of positive HIV or reactive syphilis tests in pregnancy and peripartum. We compared the rates of mother-to-child transmission of syphilis and HIV detected by case reviews to those obtained from the usual surveillance system and described the characteristic of vertical transmission cases. METHODS:This is a cross-sectional study performed with secondary data obtained from official government sources, for all the country cases of maternal to child transmission of HIV and syphilis from 2012 to 2017, with descriptive analyses. For congenital syphilis analyses, the following pregnancy characteristics were investigated: number of antenatal checks, gestational age at pregnancy diagnosis, gestational age at syphilis test and diagnosis, adequate treatment, and treatment of partners. Sociodemographic characteristics included type of health care (public/private), maternal age, distribution of ethnic minorities, maximum educational attainment, presence of partner, planned pregnancy, drug and alcohol use, domestic violence, previous maternal diagnosis of syphilis, and previous children with congenital syphilis. RESULTS:Coverage of syphilis case reviews increased from 82% in 2014 to 97.4% in 2017. For HIV, this coverage reached 100% in 2017 and elimination of mother to child transmission was achieved. A marked decline in congenital syphilis was noted in the public health care sector, especially in the capital Montevideo, whereas the private sector has remained below the elimination target. Variables related with congenital syphilis in exposed children were late pregnancy diagnosis, <?5 antenatal checks, delayed diagnosis of gestational syphilis, lower rate of correct treatment for gestational syphilis, untreated partner, low maternal schooling, unplanned pregnancy, history of syphilis, and having other children with syphilis. CONCLUSION:The use of case reviews provided knowledge regarding the accurate number of mother-to-child transmission cases and the evolution of elimination of mother to child transmission in the country. The results suggest that rates must be adjusted, providing an opportunity to improve the reliability of surveillance data, and point the need to address specific gaps in order to improve the quality of care during pregnancy, delivery, and the neonatal period.

Project description:BackgroundThe long-term impact of sexual transmission on the hepatitis B virus (HBV) infection in China remains unclear. This study aims to estimate the independent influence of sexual transmission on HBV infection.MethodsBased on the natural history of HBV infection and three national serosurvey data of hepatitis B in China, we developed an age- and sex-specific discrete model to describe the transmission dynamics of HBV. The initial conditions of the model were determined according to the age- and sex-specific national serosurvey data in 1992. Based on the national survey data of hepatitis B in 1992 and 2006, by using the Markov Chain Monte Carlo (MCMC) method, we estimated the age- and sex-specific seroclearance rates of hepatitis B surface antigen (HBsAg) and the horizontal transmission rates as well as their 95% confidence intervals (CI). Then we used the age- and sex-specific national serosurvey data of hepatitis B in 2014 to test the accuracy of our model-based estimation. Finally, we evaluated the independent impact of sexual transmission on HBV infection and discussed the long-term effect of promotion of condom use in China.ResultsWe estimated that the annual rates of HBsAg seroclearance for males and females aged 1-59 years were respectively 1.04% (95% CI, 0.49-1.59%) and 1.92% (95% CI, 1.11-2.73%). Due to sexual transmission, in 2014, the total number of chronic HBV infections in people aged 0-100 years increased 292,581, of which males increased 189,200 and females increased 103,381. In 2006, the acute HBV infections due to sexual transmission accounted for 24.76% (male: 31.33%, female: 17.94%) and in 2014, which accounted for 34.59% (male: 42.93%, female: 25.73%). However, if the condom usage rate was increased by 10% annually starting in 2019, then compared with current practice, the total number of acute HBV infections from 2019 to 2035 would be reduced by 16.68% (male: 21.49%, female: 11.93%). The HBsAg prevalence in people aged 1-59 years in 2035 would be reduced to 2.01% (male: 2.40%, female: 1.58%).ConclusionsSexual transmission has become the predominant route of acute HBV infection in China, especially for men. The promotion of condom use plays a significant role in reducing the cases of acute HBV infection.

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What could re-infection tell us about R0? A modeling case-study of syphilis transmission.

Publications

What could re-infection tell us about R<sub>0</sub>? A modeling case-study of syphilis transmission.

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