SARS-CoV-2 seroconversion among 4040 Egyptian healthcare workers in 12 resource-limited healthcare facilities: A prospective cohort study

Abstract

Background: We examined Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) seroconversion incidence and risk factors 21 days after baseline screening among healthcare workers (HCWs) in a resource-limited setting.

Methods: A prospective cohort study of 4040 HCWs took place at 12 university healthcare facilities in Cairo, Egypt; April-June 2020. Follow-up exposure and clinical data were collected through online survey. SARS-CoV-2 testing was done using rapid IgM and IgG serological tests and reverse transcriptase-polymerase chain reaction (RT-PCR) for those with positive serology. Cox proportional hazards modelling was used to estimate adjusted hazard ratios (HR) of seroconversion.

Results: 3870/4040 (95.8%) HCWs tested negative for IgM, IgG and PCR at baseline; 2282 (59.0%) returned for 21-day follow-up. Seroconversion incidence (positive IgM and/or IgG) was 100/2282 (4.4%, 95% CI:3.6-5.3), majority asymptomatic (64.0%); daily hazard of 0.21% (95% CI:0.17-0.25)/48 746 person-days of follow-up. Seroconversion was: 4.0% (64/1596; 95% CI:3.1-5.1) among asymptomatic; 5.3% (36/686; 95% CI:3.7-7.2) among symptomatic HCWs. Seroconversion was independently associated with older age; lower education; contact with a confirmed case >15 min; chronic kidney disease; pregnancy; change/loss of smell; and negatively associated with workplace contact.

Conclusions: Most seroconversions were asymptomatic, emphasizing need for regular universal testing. Seropositivity was three-fold that observed at baseline. Cumulative infections increased nationally by a similar rate, suggesting HCW infections reflect community not nosocomial transmission.

Keywords: COVID-19; SARS-CoV-2; asymptomatic; cohort; healthcare workers; seroconversion.

Figure 1

Flowchart of the cohort study and test results

Figure 2

Symptoms at baseline and follow-up among symptomatic health care workers

Figure 3

Follow-up test results of the 170 health care workers who were infected at baseline Note: a Numbers do not add to 100% at follow-up because of the overlap between groups. Groups with equal number of asterisks are the same cases. b PCR test was not done for 29/30 in this group.

Figure 4

Number of infected/seroconverted healthcare workers (HCWs) at baseline and follow up screening in Ain Shams University (ASU) hospitals or medical centers by date of onset of symptoms (bar chart, left y-axis) and daily confirmed COVID-19 cases detected through symptomatic-based testing in Egypt (line graph, right y-axis). The mitigation measures and remarkable events are shown at the national level (red color, non-italic) and at ASU level (blue color, italic).