27 years of the HIV epidemic amongst men having sex with men in the Netherlands: an in depth mathematical model-based analysis.

Background: There has been increasing concern about a resurgent epidemic of HIV-1 amongst men having sex with men in the Netherlands, which has parallels with similar epidemics now occurring in many other countries.

Methods: A transmission model applicable to HIV-1 epidemics, including the use of antiretroviral therapy, is presented in a set of ordinary differential equations. The model is fitted by maximum likelihood to national HIV-1 and AIDS diagnosis data from 1980 to 2006, estimating parameters on average changes in unsafe sex and time to diagnosis. Robustness is studied with a detailed univariate sensitivity analysis, and a range of hypothetical scenarios are explored for the past and next decade.

Results: With a reproduction number around the epidemic threshold one, the HIV-1 epidemic amongst men having sex with men in the Netherlands is still not under control. Scenario analysis showed that in the absence of antiretroviral therapy limiting infectiousness in treated patients, the epidemic could have been more than double its current size. Ninety percent of new HIV transmissions are estimated to take place before diagnosis of the index case. Decreasing time from infection to diagnosis, which was 2.5 years on average in 2006, can prevent many future infections.

Conclusions: Sexual risk behaviour amongst men having sex with men who are not aware of their infection is the most likely factor driving this epidemic.