A total of 1,320 HCPs were invited, including 476 seen by OH, 494 assigned to a designated COVID-19 unit, 388 assigned to a unit that experienced a COVID-19 HCP-outbreak, and 378 assigned to a matched control unit (non-COVID unit and without HCP-outbreak). Some HCPs are counted in multiple categories (e.g. seen by OH and worked in an HCP-outbreak unit). Among all invited, 654 HCPs participated in serologic testing (623 completed surveys). Participation was similar between cohorts: OH invited cohort (57.4% (273/476)), COVID-19 designated unit (55.7% (275/494), COVID-19 HCP-outbreak unit (50.7% 197/388), and matched non-COVID-19, non-HCP-outbreak control unit (50.0% (198/378). Cohort subsets and participant characteristics are provided in Table 1. Compared to all invited HCP, participants with prior COVID-19 PCR-positivity were more likely to participate (8.3%, 54/654 versus 7.0%, 92/1,320), though not statistically significant, p = 0.35. A total 87 (13.3%) HCPs were found to be seropositive for COVID-19 by either serology assay. Fourteen specimen tested by FDA-EUA were reflexed to alternate FDA-EUA testing with 2 reactive results. Countywide test-positivity during the study period was 7.2% (1,651/22,882).
On bivariate testing, seropositive and seronegative participants were similar in age, gender, race, comorbidities, HCP role, COVID-19 patient care (EHR or self-report), performance of an AGP, assignment to an ICU, and assignment to a COVID-19-designated units (Table 1). Seropositivity was higher among HCPs seen in OH, prior symptomatic COVID-19, those assigned to a HCP-outbreak unit, Latino ethnicity, and those living in a zip code where ≥ 25% of residents live in households with more than 1.5 occupants per room (Table 1). Notably, 60.8% (N = 52) of seropositive HCP never cared for a COVID-19 patient based upon EHR documentation (52.9% (N = 46) based upon survey self-report).
The majority (62/87, 71.3%) of seropositive HCPs reported at least one COVID-19 symptom preceding sero-testing; most (47/87, 54.0%) had symptoms ≥ 30 days before testing. Anosmia occurred in 34.5% (N = 30) of seropositive compared to 4.9% (N = 28) of seronegative HCPs. Congestion was the only symptom not associated with COVID-19 disease in bivariate testing. All PCR-positive participants were seropositive. Latino HCPs were more likely to live in areas with higher Latino populations (64%, N = 63/98) compared to non-Latino HCPs (44%, N = 238/542, p < 0.01; see Supplemental Table A).
Multivariable regression identified male gender (OR 1.79, CI 1.05–3.04, p = 0.03), Latino ethnicity (OR 2.10, CI 1.12–3.96, p = 0.02), residence in a community with low owner-occupied housing (OR = 1.63, CI = 1.00-2.64, p = 0.05), and working in a unit with an HCP outbreak (OR 2.21, CI 1.28–3.81, p < 0.01) as significantly associated with COVID-19 infection (sero- or PCR-positive) after adjusting for HCP role, comorbidities, and documented COVID-19 patient care (Table 2). Working in a COVID-19 patient unit was associated with a lower likelihood of COVID-19 (OR 0.53, CI = 0.30–0.94, p = 0.03). No other SES variable was significantly associated with COVID-19.
Table 2
Multivariate Regression Model Evaluating Epidemiologic Risk Factors for Positive Serology or PCR (Composite)
Variable
|
OR (CI)
|
P-Value
|
Age1 (years)
|
|
0.40
|
<35
|
1.00
|
|
35 - <50
|
1.53 (0.88–2.69)
|
|
50-<60
|
1.68 (0.82–3.45)
|
|
>60
|
1.42 (0.45–4.44)
|
|
Male
|
1.79 (1.04–3.94)
|
0.03
|
HCP Role1
|
|
0.35
|
Registered nurse
|
1.29 (0.57–2.95)
|
|
Nurse Aide
|
1.02 (0.20–5.74)
|
|
Physical/Occupational Therapist
|
1.05 (0.12–9.36)
|
|
Respiratory Therapist
|
0.47 (0.20–1.13)
|
|
Physician
|
0.32 (0.07–1.43)
|
|
Environmental Services
|
0.19 (0.02–1.69)
|
|
Other-Direct Patient Care
|
0.95 (0.41–2.19)
|
|
Not Direct Pt Care
|
1.29 (0.57–2.95)
|
|
Comorbidities (Any)
|
1.01 (0.56–1.79)
|
0.98
|
COVID Patient Care by EHR2
|
1.10 (0.64–1.88)
|
0.73
|
Latino Ethnicity3
|
2.1 (1.12–3.96)
|
0.02
|
% Living in zipcode where < 58% (median) live in owner-occupied home
|
1.63 (1.00-2.64)
|
0.05
|
Intensive Care Unit
|
0.75 (0.41–1.37)
|
0.34
|
HCP COVID Outbreak Unit
|
2.21 (1.28–3.81)
|
< 0.01
|
Designated COVID Care Unit
|
0.53 (0.30–0.94)
|
0.03
|
1Referents for categorical variables: Age = < 35 years, HCP Role = Registered nurse. 2EHR = Electronic Health Record. Note self-reported aerosol generating procedure was collinear with COVID care unit and ICU variables and were not included in this model. |
Highly correlated symptoms were (rho > 0.50) were grouped together: (1) fever, chills, myalgias and (2) cough and congestion. When evaluated in a model adjusting for age, gender, ethnicity, and comorbidities, fevers/chills/myalgias (OR 2.00, CI 1.03–3.90, p = 0.04) and anosmia (OR 8.81, CI 4.44–17.50, p < 0.0001) were associated with COVID-19 (Table 3).
Table 3
Multivariate Regression Model Evaluating Clinical Characteristics Associated with Positive Serology or PCR (Composite)
Variable
|
OR (CI)
|
P-Value
|
Age1 (years)
|
|
0.13
|
<35
|
1.00
|
|
35 - <50
|
1.71 (0.91–3.27)
|
|
50-<60
|
2.47 (1.13–5.41)
|
|
>60
|
1.57 (0.42–5.86)
|
|
Male
|
1.48 (0.84–2.61)
|
0.18
|
Latino Ethnicity
|
2.06 (1.09–3.87)
|
0.03
|
Comorbidities (any)
|
0.87 (0.45–1.69)
|
0.69
|
Fever/chills/myalgias2
|
2.00 (1.02–3.98)
|
0.04
|
Cough/congestion2
|
1.08 (0.55–2.39)
|
0.83
|
Loss of smell
|
8.81 (4.43–17.59)
|
< 0.01
|
Shortness of breath
|
0.88 (0.44–1.74)
|
0.70
|
1Referent for Age = < 35 years. 2Symptoms highly correlated (> 0.50) with each other and evaluated as a composite. |
The COVAM assay identified 25 additional seropositive individuals (78 [12%]) compared to the FDA-EUA assay (53 [8%])) (Table 4), p < 0.01. The FDA-EUA assay had a higher (but not statistically significant) proportion of seropositive HCPs who reported any COVID-19 symptoms, specifically fever, chills, myalgias, fatigue, anosmia, cough, and shortness of breath, while COVAM had a higher proportion of seropositive HCPs who were asymptomatic, had only non-febrile illness, or symptoms > 75 days prior to testing. When restricting to the 41 PCR-confirmed participants (Table 5), all were seropositive by the COVAM assay while 38 (92.7%) were seropositive by the FDA-EUA assay; among the two additional patients detected by COVAM, both had symptoms more than 60 days before blood draw.
Table 4
Comparative Evaluation of FDA-EUA versus COVAM Serology by Symptom Characteristics
|
Symptom Characteristics By Serology Assay
|
Percent Seropositive Within Each Symptom Category
|
|
FDA-EUA Assay or Microarray
|
N (%) of
FDA-EUA Serology with Characteristic
|
N (%) of COVAM Serology with Characteristic
|
p-value
|
N (%) of Characteristic with Positive FDA-EUA Serology
|
N (%) of Characteristic with Positive COVAM Serology
|
Seropositive - Total
|
87
|
53
|
78
|
< 0.01
|
60.9%
|
89.7%
|
Reported to Occupational Health
|
67 (77.0)
|
46 (86.8)
|
63 (80.8)
|
NS
|
68.7%
|
94.0%
|
Any Symptom Reported
|
62 (71.3)
|
42 (79.2)
|
58 (74.4)
|
NS
|
67.7%
|
93.5%
|
No Symptom Reported
|
25 (28.7)
|
11 (20.8)
|
20 (25.6)
|
NS
|
44.0%
|
80.0%
|
Symptom Type
|
|
|
|
|
|
|
Non febrile Illness
|
19 (21.8)
|
8 (15.1)
|
16 (20.5)
|
NS
|
42.1%
|
84.2%
|
Fever
|
43 (49.4)
|
34 (64.2)
|
42 (53.8)
|
NS
|
79.1%
|
97.7%
|
Fatigue
|
49 (56.3)
|
35 (66.0)
|
46 (59.0)
|
NS
|
71.4%
|
93.9%
|
Chills
|
46 (52.9)
|
34 (64.2)
|
43 (55.1)
|
NS
|
73.9%
|
93.5%
|
Myalgia
|
47 (54.0)
|
33 (62.3)
|
45 (57.7)
|
NS
|
70.2%
|
95.7%
|
Congestion
|
42 (48.3)
|
25 (47.2)
|
39 (50.0)
|
NS
|
59.5%
|
92.9%
|
Cough
|
37 (42.5)
|
28 (52.8)
|
34 (43.6)
|
NS
|
75.7%
|
91.9%
|
Loss of smell
|
30 (34.5)
|
28 (52.8)
|
30 (38.5)
|
NS
|
93.3%
|
100.0%
|
Shortness of Breath
|
21 (24.1)
|
16 (30.2)
|
19 (24.4)
|
NS
|
76.2%
|
96.3%
|
Days Between Symptoms and Serology Sample Collection
|
|
|
|
NS
|
|
|
< 14 days
|
4 (4.6)
|
3 (5.7)
|
4 (5.1)
|
|
75.0%
|
100.0%
|
15–29 days
|
10 (11.5)
|
8 (15.1)
|
9 (11.5)
|
|
80.0%
|
90.0%
|
30–44 days
|
7 (8.0)
|
7 (13.2)
|
7 (9.0)
|
|
100.0%
|
100.0%
|
45–59 days
|
23 (26.4)
|
19 (35.8)
|
23 (29.5)
|
|
82.6%
|
100.0%
|
60–74 days
|
2 (2.3)
|
1 (1.9)
|
2 (2.6)
|
|
50.0%
|
100.0%
|
>=75 days
|
15 (17.2)
|
4 (7.5)
|
12 (15.4)
|
|
26.7%
|
80.0%
|
1P-value = chi square comparing FDA-EUA with COVAM serology. Abbreviations: FDA-EUA = Food and Drug Administration Emergency Use Authorization; COVAM = Coronavirus Antigen Microarray |
Table 5
Comparison of FDA-EUA and COVAM Seropositivity and Symptom Characteristics Among those with PCR-Confirmed COVID
Seropositive and PCR-positives
|
FDA-EUA Assay or COVAM N(%)
|
FDA-EUA Assay Serology N (%)
|
COVAM Serology N (%)
|
P-value1
|
PCR-positive - Total
|
41
|
38
|
41
|
|
Seropositive
|
41
|
38
|
41
|
|
Reported to Occ Health
|
41
|
38
|
41
|
|
No Symptom Reported
|
4
|
9.8%
|
4
|
10.5%
|
4
|
9.8%
|
0.81
|
Any Symptom Reported
|
37
|
90.2%
|
34
|
89.5%
|
37
|
90.2%
|
0.81
|
Symptom Type
|
|
|
|
|
|
|
|
Fever
|
31
|
75.6%
|
30
|
78.9%
|
31
|
75.6%
|
0.77
|
Non febrile Illness
|
6
|
14.6%
|
4
|
10.5%
|
6
|
14.6%
|
0.84
|
Fatigue
|
31
|
75.6%
|
29
|
76.3%
|
31
|
75.6%
|
0.89
|
Chills
|
30
|
73.2%
|
28
|
73.7%
|
30
|
73.2%
|
0.90
|
Myalgia
|
30
|
73.2%
|
28
|
73.7%
|
30
|
73.2%
|
0.90
|
Congestion
|
21
|
51.2%
|
19
|
50.0%
|
21
|
51.2%
|
0.94
|
Cough
|
24
|
58.5%
|
23
|
60.5%
|
24
|
58.5%
|
0.91
|
Loss of smell
|
27
|
65.9%
|
26
|
68.4%
|
27
|
65.9%
|
0.87
|
Shortness of Breath
|
15
|
36.6%
|
14
|
36.8%
|
15
|
36.6%
|
0.93
|
Days Between Symptoms and Serology Sample Collection
|
|
|
|
|
|
|
|
< 14 days
|
4
|
9.8%
|
3
|
7.9%
|
4
|
9.8%
|
0.96
|
15–29 days
|
7
|
17.1%
|
6
|
15.8%
|
7
|
17.1%
|
|
30–44 days
|
7
|
17.1%
|
7
|
18.4%
|
7
|
17.1%
|
|
45–59 days
|
17
|
41.5%
|
16
|
42.1%
|
17
|
41.5%
|
|
60–74 days
|
1
|
2.4%
|
1
|
2.6%
|
1
|
2.4%
|
|
>=75 days
|
1
|
2.4%
|
1
|
2.6%
|
1
|
2.4%
|
|
1P-value = chi square comparing FDA-EUA with COVAM serology. Abbreviations: FDA-EUA = Food and Drug Administration Emergency Use Authorization; COVAM = Coronavirus Antigen Microarray |
During the study period, which occurred before implementation of universal masking and before mandatory N95 use, there were three units with HCP-outbreaks involving a total of 18 HCPs; of these, 8 (44.4%) were exposed to an ill coworker, 6 (33.3%) had no known exposure source, and 3 (16.7%) had a community exposure source. Only 1 (5.6%) HCP infection was plausibly related to patient exposure due to breach of personal protective equipment (PPE). The first outbreak began with an HCP who had traveled to an area with widespread COVID-19 and had never cared for a COVID-19 patient; this HCP developed muscle and joint pains within the incubation period while at work followed by a sore throat the next day, prompting symptom report and testing. While symptomatic, the HCP interacted directly with two other HCP who subsequently developed COVID-19 within 4–5 days. Their interactions involved hand-off of a nursing cell phone and sharing lunch in a breakroom.
The second outbreak began with a HCP who had no clear source for COVID-19 at work or in the community. The HCP developed symptoms while working and likely infected three other coworkers who worked the same shift. These HCPs also developed symptoms while working and resulted in a cascade of four additional COVID-19 infections in HCPs who worked during the same shift and/or shared spaces (e.g., breakroom, nursing station, skills class). One physician who did not regularly work on the unit spent less than 1 hour reviewing charts at the nursing station and developed COVID-19 without having entered a COVID-19 patient room.
In the third outbreak, a potluck led to 6 HCPs developing COVID-19. Preceding the potluck, a patient tested positive for COVID-19 after being unrecognized while admitted. This patient underwent emergent resuscitation and intubation before COVID-19 diagnosis, but none of the code blue providers developed COVID-19. Five of the six HCPs had not provided care for a COVID-19 patient in the weeks prior to developing symptoms. The last HCP was an administrative staff that assisted with obtaining supplies during the code blue and did not have direct patient contact; based on exposure history, this HCP most likely acquired illness from symptomatic coworkers in the nursing station.