SARS-CoV-2 IgG Seropositivity and Acute Asymptomatic Infection Rate among Firefighter First Responders in an Early Outbreak County in California

Figures & data

Figure 1. Geographic distribution of home residencies of participants..

Table 1. Characteristics of study participants and proportion with IgG antibodies or SARS-CoV-2

	Total	IgG Positive		SARS-CoV-2 PCR Positive
	N (%)	n (% of N)	Relative Risk (95% CI)	n (% of N)	Relative Risk (95% CI)
Total	983	25 (2.5)		9 (0.9)
Age, years
18-34	206 (21)	2 (1)	reference	2 (1)	reference
35-49	556 (56.6)	17 (3.1)	3.15 (0.73–13.51)	3 (0.5)	0.56 (0.09–3.3)
50 or older	221 (22.5)	6 (2.7)	2.8 (0.57–13.7)	4 (1.8)	1.86 (0.35–10.07)
Race/ethnicity*
White (non-Hispanic)	594 (60.4)	8 (1.3)	reference	6 (1)	reference
Hispanic	192 (19.5)	9 (4.7)	3.48 (1.36–8.9)	3 (1.6)	1.55 (0.39–6.13)
Asian or Pacific Islander (non-Hispanic)	78 (7.9)	3 (3.8)	2.86 (0.77–10.54)	0	–
Black (non-Hispanic)	26 (2.6)	1 (3.8)	2.86 (0.37–21.99)	0	–
Other or did not answer	93 (9.5)	4 (4.3)	3.19 (0.98–10.39)	0	–
Number of people living in home^†
1	45 (4.6)	2 (4.4)	reference	0	–
2+	929 (94.5)	23 (2.5)	0.56 (0.13–2.27)	9 (1)	–
Living with children
No	317 (32.2)	7 (2.2)	reference	3 (0.9)	reference
Yes	666 (67.8)	18 (2.7)	1.22 (0.52–2.9)	6 (0.9)	0.95 (0.24–3.78)
Non-work-related exposures to COVID-19
0 people	896 (91.1)	20 (2.2)	reference	9 (1)	–
1 person	43 (4.4)	2 (4.7)	2.08 (0.5–8.63)	0	–
2+ people	44 (4.5)	3 (6.8)	3.05 (0.94–9.89)	0	–
Domestic** or international trips since 11/1/2019
No	706 (71.8)	16 (2.3)	reference	7 (1)	reference
Yes	277 (28.2)	9 (3.2)	1.43 (0.64–3.21)	2 (0.7)	0.73 (0.15–3.48)
Number of PCR tests (prior to study)
No prior PCR tests	675 (68.7)	12 (1.8)	reference	3 (0.4)	reference
1 prior PCR test	226 (23)	6 (2.7)	1.49 (0.57–3.93)	2 (0.9)	1.99 (0.33–11.84)
2+ prior PCR tests	82 (8.3)	7 (8.5)	4.8 (1.95–11.85)	4 (4.9)	10.98 (2.5–48.18)
Positive PCR result (prior to study)
No	971 (98.8)	17 (1.8)	reference	6 (0.6)	reference
Yes	12 (1.2)	8 (66.7)	38.08 (20.52–70.65)	3 (25)	40.46 (11.44–143.15)
Do you think you have had COVID-19?^‡
No, I do NOT think so	528 (54.4)	5 (0.9)	reference	3 (0.6)	reference
No, I think it is somewhat UNLIKELY	91 (9.4)	2 (2.2)	2.32 (0.46–11.78)	1 (1.1)	1.93 (0.2–18.39)
I am UNSURE if had COVID-19	186 (19.2)	3 (1.6)	1.7 (0.41–7.06)	0	–
Yes, I think it is somewhat LIKELY	142 (14.6)	5 (3.5)	3.72 (1.09–12.67)	2 (1.4)	2.48 (0.42–14.69)
Yes, I DEFINITELY think so	24 (2.5)	2 (8.3)	8.8 (1.8–43.07)	0	–

* Race/ethnicity categories defined by investigators and included because infection rates may vary by race/ethnicity.

** Domestic trips defined as trips within the continental U.S (excludes Hawaii and U.S terriorites or possessions).

^† Number includes self.

^‡ Only if no prior positive PCR test.

Table 2. Workplace exposures of Study Participants and Proportion with IgG Antibodies or SARS-CoV-2

	Total	IgG Positive		SARS-CoV-2 PCR Positive
	N (%)	n (% of N)	Relative Risk (95% CI)	n (% of N)	Relative Risk (95% CI)
Total	983	25 (2.5)		9 (0.9)
Work exposure to a confirmed SARS-CoV-2 positive patient's respiratory secretions
No	712 (72.4)	12 (1.7)	reference	7 (1)	reference
Yes	271 (27.6)	13 (4.8)	2.85 (1.32–6.16)	2 (0.7)	0.75 (0.16–3.59)
Notified of exposure to confirmed SARS-CoV-2 positve patient or colleague
No	648 (65.9)	15 (2.3)	reference	4 (0.6)	reference
Yes	335 (34.1)	10 (3)	1.29 (0.59–2.84)	5 (1.5)	2.42 (0.65–8.94)
Full PPE during exposure, % of notified
Yes, full PPE	227 (67.8)	3 (1.3)	reference	3 (1.3)	reference
No, not full PPE	90 (26.9)	5 (5.6)	4.2 (1.03–17.22)	2 (2.2)	1.68 (0.29–9.9)
Cannot recall	18 (5.4)	2 (11.1)	8.41 (1.5–47.12)	0	–
PPE breach or failure*
No	837 (85.1)	19 (2.3)	reference	9 (1.1)	–
Yes	37 (3.8)	1 (2.7)	1.19 (0.16–8.66)	0	–
Unsure	99 (10.1)	5 (5.1)	2.22 (0.85–5.83)	0	–
Prefer not to answer	10 (1)	0	–	0	–
Confidence in ability to correctly use PPE when on duty
Less than fairly confident	7 (0.7)	0	–	0	–
Fairly confident	141 (14.3)	3 (2.1)	reference	3 (2.1)	reference
Completely confident	835 (84.9)	22 (2.6)	1.24 (0.38–4.08)	6 (0.7)	0.34 (0.09–1.33)
Confidence PPE is protective when on duty
Less than fairly confident	164 (16.7)	6 (3.7)	reference	1 (0.6)	reference
Fairly confident	510 (51.9)	8 (1.6)	0.43 (0.15–1.22)	6 (1.2)	1.93 (0.23–15.91)
Completely confident	309 (31.4)	11 (3.6)	0.97 (0.37–2.58)	2 (0.6)	1.06 (0.1–11.62)
Shared close work quarters with colleague believed to be SARS-CoV-2 positive
No	680 (69.2)	10 (1.5)	reference	3 (0.4)	reference
Yes	303 (30.8)	15 (5)	3.37 (1.53–7.41)	6 (2)	4.49 (1.13–17.83)

* This only includes the period after which PPE became mandatory, 3/4/2020.