As of 31 December 2020, 2,901 MSM were included in the ACS. Every three to six months, participants complete a standardised questionnaire designed to obtain data regarding medical history, sexual behaviour and drug use, psychosocial determinants, health care use, signs of depression and other psychological disorders, and demographics. Moreover, blood is collected for diagnostic tests and storage at the ACS biobank.

 

Of the 2,901 MSM, 607 were HIV-positive at entry into the study and 263 seroconverted for HIV during follow up. In total, the GGD Amsterdam has been visited 63,154 times by MSM since 1984.

 

Inclusion criteria. Currently, the ACS enrolls MSM who

• are HIV-negative or HIV-positive

• live in Amsterdam or are closely connected to the city

• have had at least one male sexual partner in the preceding 6 months

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Over time, inclusion criteria slightly changed. In the periods 1985-1988 and 2004-2021, the ACS included MSM who were HIV-negative at baseline, while in the remaining years, HIV-positive MSM were included as well. From 1985 to 1989, the ACS included MSM who reported ≥2 male sex partners in preceding 6 months, instead of ≥1 partner. And between 1995 and 2004 inclusion was restricted to MSM of age 30 ≤30 years.

 

The observed HIV incidence among MSM participating in the ACS has changed over time. Between 1985-1993, the HIV incidence rate declined significantly, which was followed by a stable incidence between 1993 and 1996, and a rising incidence in 1996-2009. From 2009 onwards, the HIV incidence decreased significantly. In 2019, two MSM participating in the ACS seroconverted for HIV. The HIV incidence rate was 0.11 per 100 person years (95%-confidence interval (CI) 0.02-0.81) in 2019.