Temporal trends in, and risk factors for, HIV seroconversion among female sex workers accessing Zimbabwe's national sex worker programme, 2009-19: a retrospective cohort analysis of routinely collected HIV testing data.

BACKGROUND: The frequency of new HIV infections among female sex workers in sub-Saharan Africa is poorly understood. We used routinely collected data that enable unique identification of repeat HIV testers to assess temporal trends in seroconversion and identify associated risk factors for female sex workers accessing Sisters with a Voice, Zimbabwe's national sex worker programme. METHODS: We pooled HIV testing data gathered between Sept 15, 2009, and Dec 31, 2019, from 36 Sisters programme sites in Zimbabwe. We included female sex workers aged 16 years or older with an HIV-negative test and at least one subsequent programme test. We calculated HIV seroconversion rates (using the midpoint between the HIV-positive test and the last negative test as the seroconversion date) and estimated rate ratios to compare 2-year periods by using Poisson regression, with robust SEs to account for clustering by site and adjusting for age and testing frequency to assess temporal trends. We did sensitivity analyses to explore assumptions about seroconversion dates and the effects of variation in follow-up time on our conclusions. FINDINGS: Our analysis included data for 6665 female sex workers, 441 (7%) of whom seroconverted. The overall seroconversion rate was 3·8 (95% CI 3·4-4·2) per 100 person-years at risk. Seroconversion rates fell with time since first negative HIV test. After adjustment, there was evidence of a decrease in seroconversion rates from 2009 to 2019 (p=0·0053). In adjusted analyses, being younger than 25 years, and having a sexually transmitted infection diagnosis at a previous visit, were significantly associated with increased seroconversion rates. Our findings were mostly robust to sensitivity analyses, but when 1 month before an HIV-positive test was used as the seroconversion date, seroconversion rates no longer fell with time. INTERPRETATION: We identified high rates of seroconversion shortly after linkage to programme services, which emphasises the need to strengthen HIV prevention programmes from first contact with female sex workers in Zimbabwe. New infections among female sex workers remain challenging to measure, but longitudinal analysis of routine testing data can provide valuable insights into seroconversion rates and associated risk factors. FUNDING: UN Population Fund, Deutsche Gesellschaft für Internationale Zusammenarbeit, the Bill & Melinda Gates Foundation, The Global Fund to Fight AIDS, Tuberculosis and Malaria, US President's Emergency Plan for AIDS Relief, US Agency for International Development, and the Elton John AIDS Foundation.

Interpreting declines in HIV test positivity: an analysis of routine data from Zimbabwe's national sex work programme, 2009-2019.

INTRODUCTION: Early diagnosis of HIV is critical for epidemic control. To achieve this, successful testing programmes are essential and test positivity is often used as a marker of their performance. The aim of this study was to analyse trends and predictors of HIV test positivity over time and explore how an understanding of seroconversion rates could build on our interpretation of this indicator among female sex workers in Zimbabwe. METHODS: We analysed HIV test data from Zimbabwe's nationally scaled sex work programme between 2009 and 2019. We defined test positivity as the proportion of all tests that were HIV positive and measured new diagnoses by estimating seroconversion rates among women with repeat tests, defined as an HIV-positive test after at least one HIV-negative test in the programme. We used logistic regression to analyse test positivity over three time-periods: 2009-2013, 2014-2017 and 2018-2019, adjusting for potential confounding by demographic factors and the mediating effects of time since last HIV test. We calculated the seroconversion rates for the same time-periods. RESULTS: During the 10-year study period, 54,503 tests were recorded in 39,462 women. Between 2009 and 2013, 18% of tests were among women who reported testing in the previous 6 months. By 2018-2019, this had increased to 57%. Between 2018 and 2019, test positivity was 9.6%, compared to 47.9% for 2009-2013 (aOR 6.08 95% CI 5.52-6.70) and 18.8% for 2014-2017 (aOR 2.17 95% CI 2.06-2.28). Adjusting for time since last test reduced effect estimates for 2009-2013 (aOR 4.03 95% CI 3.64-4.45) and 2014-2017 (aOR 1.97 95% CI 1.86-2.09) compared to 2018-2019. Among 7573 women with an initial HIV-negative test in the programme and at least one subsequent test, 464 tested HIV positive at a rate of 3.9 per 100 pyar (95% CI 3.5-4.2). CONCLUSIONS: Test positivity decreased among women testing through the programme over time, while seroconversion rates remained high. These declines were partly driven by changes in individual testing history, reflecting comprehensive coverage of testing services and greater knowledge of HIV status, but not necessarily declining rates of seroconversion. Understanding testing history and monitoring new HIV infections from repeat tests could strengthen the interpretation of test positivity and provide a better understanding of programme performance.

Residual colonization by vaccine serotypes in rural South Africa four years following initiation of pneumococcal conjugate vaccine immunization.

BACKGROUND: We evaluated pneumococcal colonization in children and adults between the time of 7-valent pneumococcal conjugate vaccine (PCV) introduction in the immunization program in 2009 to two years after transitioning to PCV13 in 2011. METHODS: Community-based carriage surveillance was undertaken between May-November 2013 (Period-3), with similar surveys in 2009 (Period-1) and 2011 (Period-2). Households with children below two years had a similar probability of being sampled in all surveys. Nasopharyngeal swabs were processed using standard methods and serotyped by Quellung. RESULTS: In children>9-59 months old, overall pneumococcal colonization prevalence declined from 81.8% in Period-1 to 65.0% in Period-3 (p<0.001). Reductions of 70% (41.2% vs. 13.6%) in PCV7-serotypes colonization and 66% (15.3% vs. 4.4%) for the six additional PCV13-serotypes (PCV13-add6VT) were observed. There was, however, high residual colonization by PCV7-serotypes 19F (14.9% vs. 6.3%) and 23F (8.5% vs. 4.1%), despite reduction of 57% and 52%, respectively. Among individuals>12 years of age, there was 61% reduction in PCV7-serotype colonization (3.1% vs. 1.3%) and 75% decrease for PCV13-add6VT (2.1% vs. 0.6%) between Period-1 and Period-3. CONCLUSIONS: The residual prevalence of serotypes 19F and 23F, four years after introducing PCV in the South Africa, suggests ongoing community transmission and transient vaccine effects.