The ethical committees of all participating institutions have approved the general study protocol. Additional approval may be requested for certain nested projects (e.g. intervention studies).

Any HIV-infected patient being at least 18 years old can be enrolled in the SHCS. A signed informed consent is required from all patients. A specific consent is required for genetic studies (Core genetic project).

Demographic data and specific data are registered at enrollment: date of birth, sex, nationality, ethnicity, educational degree and last held professional position, sexual preference.

Other specific data are collected: results of earlier HIV tests, the most probable mode of HIV transmission, history of antiretroviral treatment, smoking history, and hypertension awareness and treatment.

Many data are collected every six months at the follow-up visits, such as: source of income, ability to work, family situation, sexual partnership and condom use. A gynecological form enquires whether the patient has undergone a gynecological examination and if a cervical smear has been performed.

At each follow-up visit, the physician has to report on following events: opportunistic diseases of HIV infection, any diagnosis of cancer, myocardial infarction, stroke, diabetes and lipodystrophy.

The follow-up visit includes the measurement of weight, blood pressure as well as waist and hip circumference.

At registration and at each follow-up visit, a spectrum of laboratory analysis is collected (all belonging to the standard of care of an HIV-positive patient). Any result concerning CD3, CD4 and CD8 cell counts and plasma viral load has to be notified, including the method used for viral load measurement and in case of undetectable viremia, the detection limit of the given analysis.

The following laboratory analyses are required every six months: leukocyte and lymphocyte counts, hemoglobin and platelets; cholesterol, HDL cholesterol, triglyceride, glucose and lactate; for patients under antiretroviral treatment ALAT, ASAT, alkaline phosphatase and creatinine also have to be reported.

Some laboratory analyses have to be done only once, normally at registration: tuberculin skin reactivity, the hepatitis B markers, serology for Toxoplasma gondii and cytomegalovirus and syphilis. Antibodies against Hepatitis C are looked for at registration and, if the result is negative every two years thereafter. Any HCV viremia and available HCV genotype are documented.

At registration and at every follow-up visit, plasma samples are frozen for further analysis. Once a year, a sample of viable cells is obtained, prepared and stored. The laboratory informs the data centre about the number of aliquots and the attributed storage number of each frozen sample.

Drugs are registered in the database if they relate to one of the following:

For antiretroviral treatment the physician has to indicate the dosage and, in case of treatment interruption, the reason of withdrawal. Since July 2003, adherence to drug treatment is also assessed.

A special form is used to transmit information about participants who are lost from follow-up or have died. For participants lost from follow-up, the latest date he was known to be alive is documented. For patients who have died, the centre has to indicate the cause of death using the ICD-10 codes, with the exception of violent deaths, for which a simple coding system is used.

All these data are registered in a central anonymous database. A unique patient number identifies all information registered.