Study Population
A total of 218 participants were enrolled in the Corona Immunitas study from the SwissPrEPared cohort. This represents 31% (218/693) of the participants in the SwissPrEPared study that visited Checkpoint Zurich during the study time period. Participants were all assigned male at birth, and almost all had a male gender identity (99%, 1% female, 1% other), Swiss (73%), German speaking (71%), highly educated (73% completed a higher technical or university degree), and employed or self-employed (85%). The median age was 40.0 (IQR: 34.0, 45.8). Most lived alone (45%) or in a household with one other person (42%). Demographic characteristics were very similar between those who were seropositive and seronegative for SARS-CoV-2 (Table 1, Figure 1). Of the 218 participants enrolled in the study, 19 tested positive for SARS-CoV-2 antibodies, corresponding to an adjusted prevalence of 8.7% (95% credible interval: 5.7-13.2%).
Table 1. Demographic and health characteristics of study participants [n (%) or median (IQR)].
|
Total
|
COVID-19 status
|
|
|
Positive
|
Negative
|
Participants
|
218
|
19 (9%)
|
199 (91%)
|
Male gender identity
|
216 (99%)
|
19 (100%)
|
197 (99%)
|
Age
|
40.0 (34.0, 45.8)
|
38.0 (35.0, 45.0)
|
40.0 (33.5, 46.0)
|
Swiss nationality
|
160 (73%)
|
15 (79%)
|
145 (73%)
|
Never smoker
|
124 (57%)
|
13 (68%)
|
111 (56%)
|
Additional household members
|
1.0 (0, 1.0)
|
0 (0, 1.0)
|
1.0 (0, 1.0)
|
Number of trips abroad February-October 2020
|
2.0 (0.8,3.0)
|
2.0 (1.0, 3.5)
|
2.0 (0, 3.0)
|
Ever vaccinated against flu
|
89 (48%)
|
6 (38%)
|
83 (49%)
|
EuroQoL self-rated health
|
88.5
|
82.5
|
89.0
|
Obligatory schooling
|
1 (0.5%)
|
0 (0%)
|
1 (1%)
|
Vocational
|
34 (16%)
|
3 (16%)
|
31 (16%)
|
Matura
|
23 (11%)
|
3 (16%)
|
20 (10%)
|
Higher technical degree
|
61 (28%)
|
5 (26%)
|
56 (28%)
|
University
|
98 (45%)
|
8 (42%)
|
90 (45%)
|
Missing
|
1
|
0
|
1
|
Employment
|
|
|
|
Employed
|
167 (77%)
|
15 (79%)
|
152 (76%)
|
Self-employed
|
18 (8%)
|
1 (5%)
|
17 (9%)
|
Studying
|
15 (7%)
|
1 (5%)
|
14 (7%)
|
Unemployed
|
13 (6%)
|
1 (5%)
|
12 (6%)
|
Figure 1. Overall comparison of differences in characteristics, social contacts, compliance with social distancing, and sexual risk behavior between those seropositive and seronegative. Differences between the seropositive and seronegative are ordered from greatest to least except for within the sexual risk taking behavior panel.
Health risk behaviors and COVID-19 seropositivity
Those who were seropositive were less likely to have ever been vaccinated against flu (38% vs. 49%). Compliance with recommended social distancing and hygiene measures was similar across those seropositive and seronegative, although the seropositive were slightly less likely to comply with stay-at-home orders (Table 2, Figure 1). Both groups reduced their social outings during the first lockdown period, but the seronegative were more socially active before, during, and after the first lockdown period, despite the fact that the seropositive were more likely to live alone (Table 1, Figure 1). Participants also reported during the course of the regular SwissPrEPared study whether they later received a COVID-19 vaccination; vaccine uptake was very high, with 94% of both the seropositive and seronegative receiving a COVID-19 vaccination (Table 2, Figure 1, n=172 (79%) of participants reported COVID-19 vaccination status).
Table 2. Differences in compliance with social distancing measures of study participants seropositive and seronegative before, during, and after the first lockdown in March 2020 [n (%) or median (IQR)]. A score of 5 corresponds to the highest compliance levels (“always”).
|
Total
|
COVID-19 status
|
|
|
Positive
|
Negative
|
Participants
|
218
|
19 (9%)
|
199 (91%)
|
How often** have you in the last 7 days…
|
Followed social distancing*** measures?
|
4.0 (4.0, 4.0)
|
4.0 (4.0, 4.0)
|
4.0 (4.0, 4.0)
|
Stayed home when possible?
|
3.0 (2.0, 4.0)
|
3.0 (1.5, 4.0)
|
3.0 (2.0, 4.0)
|
Worn a mask?
|
4.0 (4.0, 5.0)
|
4.0 (4.0, 5.0)
|
4.0 (4.0, 5.0)
|
Increased hygiene measures****
|
4.0 (4.0, 5.0)
|
4.0 (4.0, 5.0)
|
4.0 (4.0, 5.0)
|
Average number of contacts with persons outside the household per week (>15 minutes)
|
Pre-lockdown (until mid-March 2020)
|
15.0 (7.0, 25.0)
|
10.0 (5.0, 20.0)
|
15.0 (7.2, 30.0)
|
Lockdown (mid-March to mid-May)
|
2.0 (1.0, 5.0)
|
2.0 (0.5, 4.0)
|
2.0 (1.0, 5.0)
|
Present day (time point of survey)
|
7.5 (4.0, 15.0)
|
5.0 (3.5, 10.0)
|
8.0 (4.0, 15.0)
|
*172 participants (79%) reported whether they later got a COVID-19 vaccination
**Participants answered on a scale from 1 to 5, corresponding to the following frequencies: 1: never, 2: rarely, 3: sometimes, 4: often, 5: always.
***No handshakes or hugs, maintain 2m distance from other people
****Regular handwashing, sneezing into the elbow, using tissue
Sexual behaviors and COVID-19 seropositivity
185 (85%) of participants filled in at least one follow-up questionnaire about sexual behaviors between March 1, 2020 and October 6, 2020. The differences are summarized in Table 3 and Figure 1. The median number of partners reported was lower among those who were seropositive (3.8, 5.0). Of note, 33% (n=5) of those seropositive who answered the survey did not report having sexual contacts at all during the study period. The use of dating apps was also slightly lower among those who were seropositive (75% vs. 89%), although the majority of both groups used online dating apps. Those who were seropositive were also more likely to have reduced their dating app use during the pandemic (56% vs. 34%). A similar number of people were diagnosed with an STI during the study period in the seropositive and seronegative groups (82% vs. 77%).
In a logistic model including only mean partner count and number of trips abroad during the pandemic in the SwissPrEPared study population only (n=185), increasing mean partner count was not associated with seropositivity (OR: 0.9, 95% CI: 0.8, 1.0), but increasing number of trips abroad was marginally associated (p=0.06, OR: 1.14, 95% CI: 1.0, 1.3).
Table 3. Differences in sexual behaviors of study participants seropositive and seronegative before, during, and after the first lockdown in March 2020 [n (%) or median (IQR)]. Follow-up questionnaires were included if they were filled out between March 1, 2020 and October 6, 2020.
|
Total
|
COVID-19 status
|
|
|
Positive
|
Negative
|
Participants who completed at least one survey
|
185 (85%)
|
16 (84%)
|
169 (85%)
|
Number of surveys
|
330
|
30
|
300
|
Currently taking PrEP
|
164 (89%)
|
14 (88%)
|
150 (89%)
|
Partner count*
|
5.0 (2.5, 9.0)
|
3.8 (2.5, 5.1)
|
5.0 (2.5, 9.5)
|
Changes in sexual behavior during the pandemic
|
I only had sex with my steady partner
|
12 (7%)
|
0
|
12 (8%)
|
I made an agreement with one of my sexual partners to only have sex with each other (“quarantine buddy”)
|
3 (2%)
|
0
|
3 (2%)
|
I didn’t have sexual contacts during that time
|
21 (13%)
|
5 (33%)
|
16 (11%)
|
I reduced my sexual contacts
|
110 (67%)
|
9 (60%)
|
101 (67%)
|
I didn’t change my sexual behavior
|
19 (12%)
|
1 (7%)
|
18 (12%)
|
I had more sexual contacts
|
0
|
0
|
0
|
Missing
|
20
|
1
|
19
|
Use dating apps
|
117 (88%)
|
9 (75%)
|
108 (89%)
|
Use dating apps: missing
|
52
|
4
|
48
|
Changes in dating app behaviors during the pandemic among those using dating apps (n=117)
|
Use the same
|
24 (22%)
|
1 (11%)
|
23 (23%)
|
Fewer online dates
|
38 (36%)
|
5 (56%)
|
33 (34%)
|
Use more for chatting than sex
|
41 (38%)
|
3 (33%)
|
38 (39%)
|
More online dates
|
3 (3%)
|
0
|
3 (3%)
|
Other
|
1 (1%)
|
0
|
1 (1%)
|
*If participants filled out more than one follow-up survey, the number of partners they reported was averaged across all their follow-up surveys
Comparison with general population in Zurich
Of the 218 participants enrolled in the Corona Immunitas study, 19 tested positive for SARS-CoV-2 antibodies,corresponding to an adjusted prevalence of 8.7% (95% credible interval: 5.7-13.2%). When restricted to those with primary residence in Zurich (n=195, 89%), the prevalence remained 8.7% (95% CI: 5.5-13.5%), which was slightly elevated compared to that of the general population of male 20-65 year old in Zurich during that time period (5.5%, 95% credible interval: 3.8–8.2%). The estimated RR for the SwissPrEPared cohort compared to the general Corona Immunitas population after propensity score matching (Figure 2) was 1.46 (95% CI: 0.53, 4.0), indicating a 46% increased risk of SARS-CoV-2 positivity for the SwissPrEPared cohort, although not statistically significant.
Figure 2. Comparison of the differences in distribution of age, number of people living in the same household, number of trips abroad February to October 2020, and education among SwissPrEPared participants (black line) and the Corona Immunitas general male population aged 20-65 in Zurich (grey line) using density plots. The left panel shows the differences before matching and the right panel shows the differences after matching.
To see which of these factors were most strongly associated with COVID-19 infections in the pooled sample of SwissPrEPared and Corona Immunitas participants, we conducted a separate logistic regression model (Table 2). The odds of COVID-19 infection increased by 1% for every additional year of age, 5% for every additional household member, 9% for every additional trip abroad, 97% for being a member of SwissPrEPared, and 450% for those who completed only obligatory schooling (vs. having completed a university degree or higher), after adjusting for the covariates in Table 2. Only the number of trips abroad was statistically significantly associated with risk of COVID-19 seropositivity.
Table 2. Predictors of COVID-19 infection in a pooled logistic regression analysis of SwissPrEPared and general male population participants. As there was no data on sexual behavior from the general male population, these variables were omitted from the model.
|
OR
|
95% CI
|
Age
|
1.01
|
0.99, 1.04
|
Number of additional household members
|
1.05
|
0.75, 1.43
|
Number of trips abroad February-October 2020
|
1.09
|
1.02, 1.17
|
SwissPrEPared
|
1.97
|
0.84, 4.79
|
Education*
|
|
|
Obligatory schooling
|
4.50
|
0.91, 17.39
|
Vocational
|
1.15
|
0.48, 2.68
|
Matura
|
1.23
|
0.33, 3.66
|
Higher technical degree
|
0.93
|
0.38, 2.15
|
The odds ratios in bold are those significantly associated with the odds of having a health event that day (95% confidence interval does not cross the null value of 1).
*Comparison group: those who completed a university degree or higher.