Table 2.
SARS-CoV-2 infection rates among healthcare workers in Western Norway during March–December 2020.
| Variable | 1st period (March–May) N = 1,159a | 2nd period (June–Sep) N = 583a | 3rd period (October–December) N = 630a | 2020 (March–December) N = 1,214a | Prevalence per 100 HCWs in 2020 (95% CI)b | Incidence rate in cases per 100 person-years (95% CI)b |
|---|---|---|---|---|---|---|
| Seropositive for anti-spike IgGc | 66 (5.7%) | 46 (7.9%) | 71 (11.3%) | 122 (10.0%) | 10.0 (8.4–11.9) | 14.4 (12.0–17.2) |
| New seropositive cases | 66 (5.7%) | 5/542 (0.9%) | 51/610 (8.4%) | – | – | – |
| RT-PCR positive | 30/223 (13.5%) | 4/94 (4.3%) | 49/213 (23.0%) | 52/301 (17.3%) | 4.3 (3.2–5.6) | 6.1 (4.6–8.1) |
| New positive cases by serology and/or RT-PCR | 66 (5.7%) | 8/542 (1.5%) | 53/610 (8.7%) | – | – | – |
| Total positivity by serology and/or RT-PCR | 66 (5.7%) | 49 (8.4%) | 73 (11.6%) | 127 (10.5%) | 10.5 (8.8–12.3) | 15.0 (12.5–17.8) |
n/N (%).
Clopper-Pearson interval or exact method was used to estimate cumulative probabilities of the binomial distribution in a population of 33,996 employed HCWs in Bergen and Stavanger in health care and social services with healthcare education (34, 35). For incidence rate calculation, a total of 122 (serology) or 52 (RT-PCR) or 127 (serology and/or RT-PCR) SARS-CoV-2 infection diagnoses were made from 847.74 person-years at risk.
Sera were confirmed in an anti-spike IgG ELISA after screening anti-RBD Ig. HCWs were 114 (9.8%), 53 (9.1%), and 71 (11.3%) during the 1–3 periods, respectively, and 175 (14.4%) during March–December 2020.
–, not applicable; CI, confidence interval; HCWs, Healthcare workers; RT-PCR, reverse transcription polymerase chain reaction.