The main objective of this prospective observational cohort study is to investigate the epidemiology, the risk factors and ultimately the incidence of novel HIV infections among individuals at high risk for acquiring HIV via sex practices.

We will include individuals at high-risk for HIV acquisition, i.e. HIV-negative MSM and transgender individuals who (i) do not use condoms consistently with casual partners and/or with HIV-positive partners who are not on treatment and/or (ii) recently acquired an STI and/or (iii) recently used PEP and/or (iv) frequently engage in 'chemsex' within the past 12 months Important clinical information on possible vectors for transmission (including but not limited to high-risk sex practices and sexualized drug use), use of HIV pre-exposure prophylaxis, incidence of sexually transmitted infections will be assessed and laboratory parameters will be obtained from blood, urine and mucosal secretion.

Inclusion Criteria:

1. High risk for acquiring HIV defined as followed: HIV-negative MSM and transgender individuals who (i) do not use condoms consistently with casual partners and/or with HIV-positive partners who are not on treatment and/or (ii) recently acquired an STI and/or (iii) recently used PEP and/or (iv) frequently engage in 'chemsex'.
2. Age >18 years and <100 years.
3. Written informed consent for this registry study.

Exclusion Criteria:

1. Withdrawal of the written informed consent.

Patients presenting at the HIV- and/or STI ward of the Department of Dermatology at General Hospital of Vienna which are characterized as individuals at high risk for acquiring HIV will be considered as potential participants for the HIVEX registry.