ACS among men who have sex with men (MSM)
As of 31 December 2024, 3,024 MSM have been included in the ACS since its initiation. Every three to six months, participants complete a questionnaire on their medical history, sexual behaviour and drug use, mental health, and health care use. Moreover, blood is collected for diagnostic tests and storage at the ACS biobank.
Of the 3,024 MSM, 608 were living with HIV at entry into the study and 267 acquired HIV during follow up.
The inclusion criteria for the Amsterdam Cohort Studies (ACS) have evolved over time. In 1984-85, men who had had sexual contact with a man in the preceding six months were eligible, regardless of their HIV status. Between 1985-88, only HIV-negative men of all age groups living in or around Amsterdam with at least two male sexual partners in the preceding six months were eligible to participate. Between 1988-98, the cohort also included MSM with HIV. Between 1995–2004, only men aged 30 years or younger, with at least one male sexual partner in the preceding six months, were eligible. Since 2005, HIV-negative men of all ages 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. Following recommendations from the International Scientific Advisory Committee in 2013, the cohort continues to actively recruit young HIV-negative MSM (aged 30 years or younger).
Participants who acquired HIV during follow-up in the ACS remained in the cohort until 1999, after which follow-up of a subset of MSM 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 acquisition – either at study enrolment or during follow-up - continue to attend study visits at the Public Health Service Amsterdam or at an HIV treatment centre. Blood samples from these participants are stored and behavioural data are collected every six months. Clinical data from these participants are provided by Stichting hiv monitoring.
In 2023, 664 participants without HIV and 42 participants with HIV were in follow-up and had had at least one study visit in 2023 or 2024. The median age of active participants was 47 at their last study visit. The majority were born in the Netherlands and were residents of Amsterdam (84% and 79%, respectively). In total, 80% of the participants had a college degree or higher.
HIV incidence
The observed HIV incidence rate among MSM participating in the ACS has declined over time. In 1985-93, it declined significantly, then stabilised in 1993-96, before rising in 1996-2009. From 2009 onwards, the HIV incidence decreased significantly.
Further information on trends in sexual behavior, other infections such as STI and SARS-CoV-2 can be found in the ACS year report which is part of the yearly Monitoring report of Stichting hiv monitoring and in our scientific publications.
