Methods for estimating HIV prevalence: A comparison of extrapolation from surveys on infection rate and risk behaviour with back-calculation for the Netherlands

Objectives: To compare HIV prevalence estimates (total number infected) by using extrapolation from surveys on infection rate and risk behaviour (EIR) in specific segments of the population and back-calculation (BC) on report ed AIDS cases. To discuss potential sources of bias and error, and to ident ify areas for improvement of the methodology. Design: Systematic comparison and epidemiological assessment of data input, underlying assumptions, and output. Methods: Low, possibly unbiased and high estimates of HIV prevalenc e as of January 1996 for homo/bisexual men, injecting drug users, heterosex ual men and women with multiple partners, and blood transfusion recipients and haemophiliacs were derived from surveys and continuous data collections on HIV infection rate and risk behaviour in the Netherlands between 1992 a nd 1996. These were compared with estimates (point and 95% CI) by empirical Bayesian BC on AIDS cases 1982-1995. Results and conclusions: The estimate of HIV prevalence by EIR was 13,806 with low and high estimates of 9619 an d 17,700, respectively. The HIV prevalence estimate by BC was 8812 (95% CI: 7759-9867). The available data from EIR are too limited for accurate estim ates of HIV prevalence. EIR estimates could be improved considerably with m ore precise data on prevalence of risk behaviours and HIV prevalence rate f or homosexual men. More confidence can be put in the BC estimates, but thes e could be underestimates because of the age effect on incubation time, pre -AIDS treatment and relapse of risk behaviour. BC estimates could be improv ed by a better representation of the incubation time distribution (includin g the effect of age thereupon), better data on the effectiveness and uptake of pre-AIDS antiretroviral treatment and prophylaxis of opportunistic infe ctions, and on the level of underreporting.