Estimating HIV incidence in Mexico by mode of exposure: insights of the modes of transmission model (MoT)
M. De Luca1, C. Magis-Rodríguez1, E. Bravo-García1, A. Borquez2
1Centro Nacional para la Prevención y el Control del VIH/Sida, México, Dirección de Investigación Operativa, Mexico D.F., Mexico, 2Imperial College London, London, United Kingdom
Background: In the past 8 years, routine surveillance of AIDS and HIV cases as well as cross-sectional serology surveys have suggested changes in the Mexican epidemic: higher number of women, IDUs, FSW, MSW and heterosexual men living with HIV/AIDS, along with decreases in the prevalence among MSM. In order to understand these changes and plan for prevention, an improved characterisation of the current patterns of incidence is needed. With this aim, the UNAIDS MoT model was applied.
Methods: The MoT model estimates the incidence in the next year in groups with different risk behaviours in function of the number of people in each subpopulation, their number of partners and acts per partner and the HIV prevalence among partners, taking into account the effect of STIs and circumcision on transmission. Data needed to parameterize the model were put together, analysed and validated at the national and international levels to produce estimates.
Results: The model suggests that 12,000 new infections will occur in the next year in Mexico. 56% of these will happen among MSM and another 9.5% among their stable female partners. A further 9% will take place among IDUs and 13% among the low risk heterosexual population who represent about 1% and 35% of the total population respectively. The remaining groups contribute to less than 5% of the number of new infections.
Conclusions: Further data collection is needed to estimate the size of certain subpopulations such as FSW and their clients as well as to have a better understanding of their risk behaviours. It is clear that most infections will arise among MSM and their female partners. However, this is a heterogeneous population and different prevention measures must be taken to address the problem. The results also suggest that prevention efforts among IDUs would be an efficient path to restrain the epidemic.
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