Of the 2,901 MSM, 607 were HIVpositive at entry into the study and 263 seroconverted for HIV during follow up. In total, the GGD Amsterdam has been more than 63,500 times by MSM since 1984. In 1984-85, men who had had sexual contact with a man in the preceding six months were enrolled, independent of their HIV status. In the period 1985-88, HIV-negative men of all age groups were eligible to participate if they lived in, or around Amsterdam, and had had at least two male sexual partners in the preceding six months. In 1988-98, the cohort also included MSM living with HIV. In 1995–2004, only men aged 30 years or younger, with at least one male sexual partner in the previous six months, could be included the study.

 

Since 2005, HIV-negative men of all age groups have been eligible to participate in the ACS if they live in, or are closely connected to the city of Amsterdam, and have had at least one male sexual partner in the preceding six months. In line with the advice issued by the International Scientific Advisory Committee in 2013, the cohort continues additional efforts to recruit young HIV-negative MSM (aged 30 years or younger).

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HIV-seroconverters within the ACS remained in the cohort until 1999, when follow up of a selection of MSM living with HIV was transferred to the MC Jan van Goyen. In 2003, the HIV Research in Positive Individuals (Hiv Onderzoek onder Positieven, HOP) protocol was initiated. Individuals with a recent HIV infection when entering the study at the GGD Amsterdam, and those who seroconverted for HIV during follow up within the cohort, continue to return for study visits at the GGD Amsterdam, or at an HIV treatment centre. Blood samples from these participants are stored. All behavioural data are collected on a six-monthly basis by questionnaires, coordinated by the GGD Amsterdam, and clinical data are provided by SHM.

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In 2020, which was affected by the COVID-19 pandemic, 699 HIV-negative and 50 MSM living with HIV were active participants at the GGD Amsterdam; in other words, they visited the cohort at least once in 2019 or 2020. All 50 MSM living with HIV filled out behavioural questionnaires. In 2020, two new HIV-negative MSM, who were 28.7 and 48.4 years of age at inclusion, were recruited. The median age of the total group of MSM in active follow up was 44.5 (interquartile range [IQR] 34.0- 55.9) years at their last cohort visit. The majority were born in the Netherlands and were residents of Amsterdam (83.4% and 88.8%, respectively). In total, 77.2% of the participants had a college degree or higher.