The relationship between HIV prevalence in MSM and available data on HIV testing: what limits do the observed set upon the unobserved?

Estimates of total prevalent human immunodeficiency virus (HIV) infections make an important contribution to public health planning. HIV test data has become increasingly important to the monitoring of the HIV epidemic, however a large proportion of HIV infections remain undiagnosed in the early stages of infection. This thesis aims to develop a method to estimate total HIV infections in men who have sex with men (MSM) in the United Kingdom (UK) using surveillance data on HIV testing. A conceptual framework for the relationship between HIV testing and risk of HIV infection was developed. A review of literature showed that HIV testing was associated with socio-demographic factors like increasing age and area of residence. HIV testing was also associated with higher-risk behaviours such as unprotected anal intercourse and increased numbers of sexual partners. This thesis identified and quantified factors associated with both HIV testing and risk of HIV infection in MSM in the UK through two studies. The first was an analysis of a national representative study and the second a cross-sectional unlinked anonymous HIV seroprevalence study of MSM attending a genitourinary medicine clinic (GUM) in inner London. An investigation of the National Survey of Sexual Attitudes and Lifestyles found that 36.6% of MSM had HIV tested in the past 5 years. HIV testing was associated with area of residence and increased numbers of sexual partners. The unlinked anonymous study found that MSM who had HIV tested were at higher risk of HIV infection compared to MSM who had not and that history of sexually transmitted infections was associated with HIV infection. A comparative analysis with a community-recruited study of MSM provided upper and lower behavioural bounds. Finally, a model based on the conceptual framework which extrapolated all diagnosed HIV infections in MSM to give reliable estimates of total HIV infections in the general MSM population, including undiagnosed HIV infections, was developed. This thesis has provided a unique methodology to estimate total HIV infections in MSM in the UK