High Seroprevalence of anti-SARS-CoV-2 antibodies among Ethiopian healthcare workers

Abstract Background COVID-19 pandemic has a devastating impact on the economies and health care system of sub-Saharan Africa. Healthcare workers (HWs), the main actors of the health system, are at higher-risk because of their occupation. Serology-based estimates of SARS-CoV-2 infection among HWs represent a measure of HWs’ exposure to the virus and a guide to the prevalence of SARS-CoV-2 in the community. This information is currently lacking in Ethiopia and other African countries. This study aimed to develop an in-house antibody testing assay, assess the prevalence of SARS-CoV-2 antibodies among Ethiopian high-risk frontline HWs. Methods and findings A cross-sectional seroprevalence study was conducted among HWs in five public hospitals located in different geographic regions of Ethiopia. Socio-demographic and clinical data were collected using questionnaire-based interviews. From consenting HWs, blood samples were collected between December 2020 and February 2021, the period between the two peaks of COVID-19 in Ethiopia. The collected sera were tested using an in-house immunoglobin G (IgG) enzyme-linked immunosorbent assay (ELISA) for SARS-CoV-2 specific antibodies on sera collected from HWs. Of 1,997 HWs who provided a blood sample, demographic and clinical data, 50.5% were female, 74.0% had no symptoms compatible with COVID-19, and 29.0% had history of contact with suspected or confirmed patient with SARS-CoV-2 infection. The overall seroprevalence was 39.6%. The lowest (24.5%) and the highest (48.0%) seroprevalence rates were found in Hiwot Fana Specialized Hospital in Harar and ALERT Hospital in Addis Ababa, respectively. Of the 821 seropositive HWs, 224(27.3%) had history of symptoms consistent with COVID-19. A history of close contact with suspected/confirmed COVID-19 cases was strongly associated with seropositivity (Adjusted odds Ratio (AOR) =1.4, 95% CI 1.1-1.8; p=0.015). Conclusion High SARS-CoV-2 seroprevalence levels were observed in the five Ethiopian hospitals. These findings highlight the significant burden of asymptomatic infection in Ethiopia, and may reflect the scale of transmission in the general population. Author summary Why was this study done? Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a global public health threat, including Africa The actual morbidity and mortality associated with SARS-CoV-2 infection in Ethiopia underestimated due to the limited molecular testing capacity. We have limited knowledge about the seroprevalence of COVID-19 among health workers in Ethiopia. This study aimed to develop an in-house immunoglobin G (IgG) enzyme-linked immunosorbent assay (ELISA) for SARS-CoV-2 specific antibodies on sera collected from HWs and to find out the proportion of healthcare workers who have developed antibodies specific to SARS-CoV-2 from five public hospitals located in the different regions of Ethiopia. What did the researchers do and find? A cross-sectional seroprevalence study was conducted among HWs in five public hospitals located in different geographic regions of Ethiopia. Socio-demographic and clinical data were collected from recruited and consented participants using questionnaire-based interviews. Blood samples were collected from participants between December 2020 and February 2021, the period between the two peaks of COVID-19 in Ethiopia. The collected sera were tested using an in-house ELISA for SARS-CoV-2 specific antibodies on sera collected from HWs. Approximately 40% of the 1,997 healthcare workers who participated in this study had antibodies against SARS-CoV-2 infection. No association between seropositivity and study participants’ age, gender, occupation, and comorbid medical conditions. What do these findings mean? The observed high seroprevalence among healthcare workers regardless of their occupation suggests the cryptic but massive SARS-CoV-2 transmission in urban hospital settings. Most of the seropositive healthcare workers in the present study were asymptomatic, and might pose a threat to the most vulnerable populations such as individuals with comorbid medical conditions. Given the low level of vaccine roll-out (1%), this study highlights the need to strengthen health workers’ adherence to personal protection practices such as wearing face masks to protect individuals at high risk of developing severe COVID-19 illness after SARS-CoV-2 infection.