Men having sex with men serosorting with casual partners: who, how much, and what risk factors in Switzerland, 2007-2009

Table 3 Serosorting: extrapolated country MSM population

	Gaysurvey sample data							Extrapolated to country MSM population (17–74 yr.)
	Gaysurvey sample data							a) Restricted definition (sex only with men, mainly with men, and with as many women as men, lifetime)		b) Enlarged definition (at least one partner of same sex, lifetime)
	N	%	CI 95% ^c			% Among Serosorters %	Mean number of sexual partners with AI^d	N	Min_a/max_a	N	Min_b/max_b
Pooled Gaysurvey data (2007-2009)	4882	100						33,700			70,300
UAI with casual partners^a	647	13.3	12.3	-	14.2		11 ± 1	4466	4150/4798	9317	8656/10,008
Serosorting with casual partners^b	247	5.1	4.5	-	5.7	N = 247	11 ± 1	1705	1503/1925	3557	3136/4015
Serostatus declared
HIV-positive	44	0.9	0.7	-	1.2	17.8	18 ± 2	304	221/407	634	461/849
Detectable viral load and No STI^e	10	0.2	0.1	-	0.4	4.0	17 ± 5	69	33/127	144	69/265
Undetectable viral load and No STI	15	0.3	0.2	-	0.5	6.1	18 ± 4	104	67/169	216	141/352
Undetectable viral load and STI	12	0.2	0.1	-	0.4	4.9	15 ± 4	83	43/145	173	89/302
Detectable viral load and STI	7	0.1	0.1	-	0.3	2.8	24 ± 5	48	19/99	101	41/208
HIV-negative	164	3.4	2.9	-	3.9	66.4	10 ± 1	1132	968/1316	2362	2019/2744
Tested in the past 12 months	112	2.3	1.9	-	2.8	45.3	11 ± 1	773	638/928	1613	1331/1936
Not tested in the past 12 months	52	1.1	0.8	-	1.4	21.1	8 ± 1	359	268/470	749	560/980
N.A, D.K, Not tested^f	39	0.8	0.6	-	1.1	15.8	10 ± 2	269	192/367	562	400/767

a: Unprotected anal intercourse (UAI) in the past 12 month.
b: Among respondents who had UAI with casual partners in the past 12 months (N = 647).
c: Confidence interval (CI) calculated with the exact binomial distribution.
d: Anal intercourse in the past 12 months.
e: Sexually transmitted infections (STIs) in the past 12 months.
f: N.A: No answer; D.K: Don’t know.

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