Outcome of Epidemiological Investigation of COVID-19 Outbreak in a South West State of Nigeria, March to August 2020

Background: On 3rd April 2020, an outbreak of Coronavirus disease-2019 (COVID-19) was confirmed in Ondo State, Southwest Nigeria. Field investigations were conducted by the State Ministry of Health (MoH) to identify and confirm additional cases. This paper provides the outcome of the epidemiological investigation of the outbreak to further guide outbreak response activities. Methods: Field epidemiology methods coordinated by the State Public Health Emergency Operations Center (PHEOC) were used in the outbreak investigation. Suspected cases were reported through the routine Integrated Disease Surveillance and Response (IDSR) network in the State. Also, active case search/finding to communities and health facilities using the operational case definitions was conducted. Furthermore, the state COVID-19 emergency call center was established with toll-free phone number provided to members of the public to call-in to report suspected persons with symptoms consistent with the COVID-19 operational case definition (signal). All cases reported were investigated with nasopharyngeal sample collected and confirmatory testing for COVID-19 done by real-time polymerase chain reaction (RT-PCR) in a national reference laboratory. Information of each case investigated was documented using the COVID-19 case investigation form and COVID-19 line-list which captured socio-demographic characteristics, history of exposure to COVID-19, presenting symptoms, travel history and sample collection details. Data were extracted from the case investigation form and line list and analyzed using SPSS version 20, with a p-value set at < 0.05. Results: A total of 4353 suspected cases were reported and investigated, of which 1316 cases were confirmed between March 19, 2020 and August 9, 2020. The mean age of the confirmed cases was 37.8 ± 14.8 years. The highest proportion of COVID-19 cases and deaths occurred in the age group 20 - 39 years (50.6%) and ≥60 years (13.5%), respectively. More males (52.4%) were affected than females (45.8%). There were 404 (30.7%) healthcare workers infection. About a quarter (325; 24.7%) of the cases was symptomatic and presented with key symptoms such as cough (98/325; 30.2%) and fever (74/325; 22.8%) during the investigation. A case fatality rate (CFR) of 2.2% was recorded in 7 of the 17 Local Government Areas (LGAs) where confirmed cases were reported in the State. Most of the confirmed cases, 1169 (88.8%) reside in urban LGAs of the State. The epidemic curve shows a propagated pattern of transmission with the outbreak reaching its peak on July 2, 2020. Significantly, higher proportion of death was recorded in the age group ≥ 60 years (14; 13.5%) and among males (26; 3.6%) (p < 0.001). Conclusions: Our investigation found high transmission of COVID-19 infection among urban residents (LGAs) and health care workers with high mortality among males in older age group in the State. Hence, we recommend intensified risk communication and use of community structures to ensure compliance with public health COVID-19 preventive protocols including enforcing infection prevention and control compliance, particularly among high-risk groups.