Evolution of recruitment

The Swiss HIV Cohort Study (SHCS) is a large cohort study enrolling patients prospectively since 1988. Some data going back to 1981 have been collected retrospectively. As of December 2014, a total of 18'850 persons have been enrolled in the SHCS. Since 1997, the annual number of newly registered patients has been decreasing from 834 in 1997 to about 500 in 2002 and has slightly increased afterwards until 2009 (Figure 1).

The largest proportion of patients were recruited in Swiss University Hospital infectious disease outpatient clinics in Zurich (37.3%). In the 3 other Swiss University Hospital infectious disease outpatient clinics of Lausanne, Geneva and Bern, each contributes about 14-16% of patients, the University Hospital infectious disease outpatient clinics of Basel has 10%. Lugano and St.Gallen, which are two large cantonal hospitals, have 3-6% (Figure 2).


Figure 1: Patients newly registered each year in the Swiss HIV Cohort Study (SHCS), 1984 - 2014

Figure 2: Distribution of patients ever registered in the SHCS by clinical centre (N=18'998)

A unique feature of the SHCS is the large proportion of women (24.7% of women newly registered in 2014) (Figure 3).

The main three transmission groups IDU (Intravenous Drug User), MSM (Men having Sex with Men) and HET (heterosexual contacts) are well represented. Among patients belonging to the transmission group IDU we further distinguish patients where the most probable cause of infection was intravenous drug use from those where the transmission might have occurred sexually (Figure 4).


Figure 3: Distribution of new patients registered each year in the SHCS by gender, 1986 - 2014

Figure 4: Distribution of patients ever registered in the SHCS by presumed mode of infection, 1986 - 2014

The mean age of patients at the time of registration has increased over the years: for females, it was 30 in 1990 and 38 in 2014; for males, it was 34 in 1990 and 41 in 2014 (Figure 5).

Figure 6 indicates that the median CD4 cell count at the time of registration, first decreased over time for both sex until 1995, then increased up to nowadays though with some fluctuations.


Figure 5: Mean age at registration in the SHCS by gender, 1986 - 2014

Figure 6: Mean CD4 cell count at registration in the SHCS by gender, 1986 - 2014

With the advent of combined Antiretroviral Therapy (cART) in 1995-1996 and the hope to eradicate the virus by early treatment, the median CD4 cell count at the initiation of the therapy raised very rapidly. However, due to the likely impossibility to eradicate completely the virus we observed a down-turn in the curve indicating that the guidelines for initiating a treatment evolved toward lower values of the CD4. Noteworthy, however, is that since 2002 an up-turn of the curve is generally observed with cART therapy started at higher levels of CD4, particularly regarding MSM (Figure 7).

Mortality has substantially decreased since cART became available in 1996 and is still steadily decreasing (Figure 8).


Figure 7: Median CD4 cell count at initiation of cART in treatment naïve patients by presumed mode of infection, in the SHCS by gender, 1996 - 2014

Figure 8: Probability of dying and dropping out in the SHCS, 1991 - 2014

Until end of 2014, 25.7% (4'839) of study participants died, and 5'054 (26.8%) were reported lost from follow-up (drop-outs), because they did not answer, left the country or did not want to participate any more in the study. The number of patients currently followed up in the SHCS is 9’199, whereas this number was 6’393 in 2005. The average follow-up visits per patient in 2014 was 1.8.

The number of patients followed up by other outpatient clinics (e.g. Bienne, Burgdorf, Neuchâtel, etc.) and by private practitioners increased continuously (figure 10). The distribution of private physician is not even. In Geneva, for example, over 61% of participating patients were under the care of private physicians during the year 2013, whereas this figure was less than 20% for Bern (figure 11).


Figure 9: Annual number of patients seen at least once in the SHCS, 1984 - 2014

Figure 10: Annual number of patients visits by type of health care provider in the SHCS, 1987 - 2014

Figure 11: Distribution of visits in the SHCS in 2014, by type of health care provider