Background
Influenza is one of the leading causes of illness and death in people of all ages. Nigeria established the National Influenza Sentinel Surveillance (NISS) in 2008. We analyzed the surveillance data collected by the NISS to describe the epidemiology of influenza, identify the circulating influenza virus (IFV) types and sub-types, and describe comorbidities among influenza cases.
Methods
We extracted data from the NISS database from January 2010 to December 2020. The surveillance system enrolls out-patients with influenza-like illness (ILI), in-patients with Severe Acute Respiratory Infection (SARI), and patients with symptoms suggestive of Novel H1N1 and Avian Influenza. Variables of interest include age, sex, date of onset, comorbidities, and influenza virus types and sub-types. Data were summarized using means and proportions and presented in tables and charts.
Results
A total of 1,421/13,828 (10.3%) suspected cases tested positive for IFV, out of which 1,243 (87.5%) were ILI patients, 175 (12.3%) SARI patients, and 3 (0.2%) were Novel H1N1 patients. Males accounted for 770/1,421(54.2%) of the confirmed cases. The median age of confirmed cases was 3 years (range: <1month–97 years). Children 0-4 years accounted for 985/1,421 (69.3%) of all cases. The predominant subtypes over the 11-year period were A/H1N1 pdm09, A/H1N1 pdm09 and A/H3 and these subtypes were different for specific years. B Victoria had its highest incidence in 2018 when sub-typing for IFV B commenced. Heart disease and chronic shortness of breath were the most common co-morbidities identified among confirmed cases.
Conclusion
Influenza remains a significant cause of respiratory illness. Age-group 0-4 years accounted for the highest proportion of cases. IFV A & B were the circulating virus type in Nigeria. We recommended that influenza surveillance should include the sub-typing of all influenza cases to aid in the identification and response to new epidemics or pandemics. Cases should be followed up to determine the outcome.