Table 2.

Risk factors for SARS-CoV-2 seroconversion

	Baseline n = 2794						Follow up n = 2227
	n total	n sero-conversion	% sero-conversion	OR	95% CI	p value	n total	N sero-conversion	% Sero-conversion	OR	95% CI	p value
Age
Per 10 years	2794	99		1.10	0.93–1.29	0.267	2227	290		0.99	0.98–1.00	0.104
Sex
Female	2197	76	3.5				1763	227	12.9
Male	597	23	3.9	1.12	0.68–1.77	0.645	464	63	13.6	1.06	0.78–1.43	0.689
Blood group
0	722	25	3.5				695	74	10.6
A	693	32	4.6	1.35	0.79–2.32	0.271	654	107	16.4	1.64	1.20–2.26	0.002
B	182	7	3.8	1.12	0.44–2.49	0.802	173	23	13.3	1.29	0.77–2.09	0.324
AB	64	0	0.0	0.00	0.00–15.72	0.977	64	14	21.9	2.35	1.20–4.35	0.009
unknown	1133	35	3.1	0.89	0.53–1.51	0.658	641	72	11.2	1.06	0.75–1.50	0.732
Employment rate
< 60%	514	15	2.9				410	61	14.9
60–79%	359	14	3.9	1.35	0.64–2.85	0.427	293	38	13.0	0.85	0.55–1.31	0.473
80–100%	1873	69	3.7	1.27	0.74–2.33	0.405	1436	182	12.7	0.83	0.61–1.14	0.245
Profession
Employee without patient exposure	559	11	2.0				478	48	10.0
Physician	376	9	2.4	1.22	0.49–2.98	0.660	273	28	10.3	1.02	0.62–1.66	0.925
Nurse	1118	51	4.6	2.38	1.28–4.85	0.010	886	143	16.1	1.72	1.23–2.46	0.002
Other employee with patient exposure	741	28	3.8	1.96	0.99–4.14	0.063	590	71	12.0	1.23	0.83–1.81	0.304
Type of patient exposure
None	845	18	2.1				709	74	10.4
No COVID-19 patients	1211	34	2.8	1.33	0.75–2.41	0.337	493	50	10.1	0.97	0.66–1.41	0.869
With COVID-19 patients	701	46	6.6	3.23	1.89–5.76	< 0.001	937	157	16.8	1.73	1.29–2.33	< 0.001
Unprotected exposure to COVID-19 patient
No	664	42	6.3				880	149	16.9
Yes	38	4	10.5	1.74	0.50–4.63	0.315	58	9	15.5	0.90	0.40–1.79	0.780
ICU employee
No	1675	67	4.0				1219	177	14.5
Yes	253	14	5.5	1.41	0.75–2.47	0.259	213	30	14.1	0.97	0.63–1.45	0.868
Employee at COVID-19 ward
No	1681	52	3.1				1151	148	12.9
Yes	246	29	11.8	4.19	2.57–6.69	< 0.001	281	59	21.0	1.80	1.28–2.51	0.001
Employee in emergency unit
No	1531	57	3.7				1114	166	14.9
Yes	396	24	6.1	1.67	1.00–2.69	0.041	318	41	12.9	0.85	0.58–1.21	0.37
Exposure to SARS-CoV2 infected co-worker
No	2368	58	2.4				1665	200	12.0
Yes	383	40	10.4	4.64	3.04–7.04	< 0.001	445	73	16.4	1.44	1.07–1.92	0.015
Non-occupational exposure to SARS-CoV2 infected person
No or unknown	2660	83	3.1				1810	166	9.2
Household	30	12	40.0	20.70	9.43–43.99	< 0.001	172	82	47.7	9.02	6.43–12.67	< 0.001
Outside household	61	3	4.9	1.61	0.39–4.46	0.432	157	33	21.0	2.64	1.72–3.95	< 0.001
Child (ren)living same in household
No	2081	73	3.5				1635	209	12.8
Yes	669	25	3.7	1.07	0.66–1.67	0.781	504	72	14.3	1.14	0.85–1.51	0.383
Regional incidence*
Low	2393	79	3.3				1879	219	11.7
Medium	141	1	0.7	0.16	0.01–1.94	0.151	129	23	17.8	1.68	0.78–3.61	0.184
High	260	19	7.3	1.88	0.50–7.12	0.353	219	48	21.9	2.06	1.10–3.89	0.025
FFP2 mask policy*
Specific use	1993	68	3.4				1636	204	12.5
General use	801	31	3.9	0.70	0.20–2.40	0.567	591	86	14.6	1.14	0.60–2.16	0.693

Participants who seroconverted before the baseline assessment (n = 99) were excluded for analysis of seroconversion at follow-up. Note that total n for individual risk factors may be smaller due to missing values

^*For these factors determined at institutional level regression models included health care institutions as random effect