Showing papers by "Sharmistha Mishra published in 2013"

Screen more or screen more often? Using mathematical models to inform syphilis control strategies

Abstract: Syphilis incidence among men who have sex with men (MSM) continues to rise despite attempts to increase screening and treatment uptake. We examined the marginal effect of increased frequency versus increased coverage of screening on syphilis incidence in Toronto, Canada. We developed an agent-based, network model of syphilis transmission, representing a core population of 2,000 high-risk MSM. Epidemiological and biological parameters were drawn from regional surveillance data and literature-derived estimates. The pre-intervention period of the model was calibrated using surveillance data to identify 1000 credible simulations per strategy. Evaluated strategies included: annual syphilis screening at baseline coverage, increased screening frequency at baseline coverage, and increased coverage of annual screening. Intervention impact was measured as annual prevalence of detected infectious cases and syphilis incidence per year over 10 years. Of the strategies evaluated, increasing the frequency of syphilis screening to every three months was most effective in reducing reported and incident syphilis infections. Increasing the fraction of individuals tested, without increasing test frequency, resulted a smaller decline in incidence, because reductions in infectious syphilis via treatment were counterbalanced by increased incident syphilis among individuals with prior latent syphilis. For an equivalent number of additional tests performed annually, increased test frequency was consistently more effective than improved coverage. Strategies that focus on higher frequency of testing in smaller fractions of the population were more effective in reducing syphilis incidence in a simulated MSM population. The findings highlight how treatment-induced loss of immunity can create unexpected results in screening-based control strategies.

Sexual behaviour, structural vulnerabilities and HIV prevalence among female sex workers in Pakistan

Abstract: Background We sought to describe differences in individual and structural vulnerabilities faced by female sex workers (FSWs) in Pakistan between 2006 and 2011, and to characterise risk factors for inconsistent condom use and HIV prevalence in this population. Methods To describe differences in vulnerabilities, we analysed behavioural data from serial cross-sectional surveys conducted across nine cities in 2006 and 2011. Using data from 12 cities in 2011, we used logistic regression to characterise risk factors for (a) inconsistent condom use in the past month (N=6987), and (b) HIV (N=4301). Results Compared to FSWs in 2006, FSWs in 2011 were significantly more likely to solicit clients via cell phones, and to report a larger client volume and anal sex with clients, but also consistent condom use with clients (30.0% vs 23.6% in 2006). In 2011, independent risk factors for inconsistent condom use with clients included: recent sexual violence, recent sex with a person who injects drugs, and absence of programme exposure. HIV prevalence was 0.63% (95% CI 0.43% to 0.92%) in 2011, and was associated with a recent history of injection drug use and absence of programme exposure. Conclusions While condom use with clients was higher in 2011, protective behaviours remained low and vulnerabilities related to sex work may have risen. HIV is emerging in this population and an adaptive HIV prevention programme that addresses different vulnerabilities and the intersection of sexual networks with injection drug use is needed.

S04.6 Examining the Population-Level Impact of Scaling-Up ART For FSWs Across Epidemic Context

Abstract: In this presentation, we will summarise the results of a recent systematic review of the published literature on the key parameters of the treatment cascade among female sex workers. Using different examples from transmission dynamics modelling studies of HIV transmission and ART use, we will discuss the potential impact of scaling-up ART for FSWs in contrasting epidemiological settings. We will present results of the impact of ART programmes in settings with different HIV prevalence levels in the general population (very low, low/medium, high) and different history of condom use interventions and level of ART scale-up already achieved. For example, we will compare the impact of different ART scale-up scenarios and eligibility criteria in districts of India (low prevalence settings) where there has been and there has not been a large-scale condom use intervention implemented in recent years. Other settings with higher HIV prevalence such as Benin, Burkina Faso, Columbia or Kisumu will be considered. We will also contrast the impact of ART programme targeted to FSW on HIV transmission in the general population and assess the influence of key parameters of the treatment cascade on the impact of ART among FSWs.

O13.5 The HIV Modes of Transmission Model: A Systematic Review of Its Findings and Adherence to Guidelines

Abstract: Background The HIV Modes of Transmission model (MOT) estimates the annual percentage distribution of new HIV infections (PNI) by key risk groups. It was designed to guide country-specific HIV prevention policies. To determine if the MOT produced context-specific recommendations, we analysed the MOT results by regions and epidemic types and explored the factors (e.g. data inputs, adherence to guidelines) influencing the differences. Methods We systematically searched MEDLINE, EMBASE, UNAIDS reports, and contacted UNAIDS country directors for published MOT results from 2003 (1st published MOT). Results We included 4 journal articles and 20 UNAIDS reports covering 29 countries. The largest PNI was among the low-risk group (one heterosexual partner) in 13 countries [range 26–63%], and increased with low-risk population size. The estimated PNI among female sex workers (FSWs) was universally low [median 1.3%, range 0.04–14.4%], and showed little variability by region and epidemic type despite variation in sexual behaviour e.g. number of partners. In India and Thailand, where FSWs play an important role in transmission, the PNI among FSWs was 2% and 4% respectively. In contrast, the PNI among men who have sex with men (MSM) varied across regions [MSM, range 0.1–89%] and increased with MSM population sizes. The PNI among people who inject drugs [PWID, range 0–82%] was largest in ‘early-phase’ epidemics with low overall HIV prevalence. Most MOT studies are being conducted and reported as per guidelines. However, many countries (n = 23) reported data limitations - especially on high-risk groups - when parameterising the MOT. Conclusion Although countries are generally performing the MOT as per guidelines, results showed little variation in MOT outputs (except MSM and PWID) by regions and epidemic types. Homogeneity in MOT outputs for FSWs, clients and low-risk population may limit the utility of MOT for guiding country-specific interventions in heterosexual HIV epidemics.