Influenza Sentinel Surveillance among Patients with Influenza-Like-Illness and Severe Acute Respiratory Illness within the Framework of the National Reference Laboratory, Niger, 2009-2013

BACKGROUND: Little is known about the epidemiology of influenza in Africa, including Niger. We documented the epidemiology of seasonal and pandemic influenza among outpatients with influenza-like-illness (ILI) and inpatients with severe acute respiratory illness (SARI) presenting at selected sentinel sites in Niger from April 2009 through April 2013. METHODS: Patients meeting the ILI or the SARI case definitions and presenting at the outpatient or inpatient departments of selected sentinel sites were enrolled. Epidemiological data and nasopharyngeal swabs were collected. The respiratory samples were tested by real-time reverse transcription polymerase chain reaction. RESULTS: From April 2009 to April 2013, laboratory results were obtained from 1176 ILI and 952 SARI cases, of which 146 (12%) and 54 (6%) tested positive for influenza virus, respectively. The influenza positivity rate was highest in the 5-14 year age-group (32/130; 24% among ILI patients and 6/61; 10% among SARI patients) followed by the 1-4 year age-group (69/438; 16% among ILI patients and 32/333; 9% among SARI patients). Of the 200 influenza positive cases 104 (52%) were A(H1N1)pdm09, 62 (31%) were A(H3N2) and 34 (17%) were B. Influenza viruses were detected predominantly from November to April with peak viral activity observed in February. CONCLUSIONS: The Niger sentinel surveillance system allowed to monitor the circulation of seasonal influenza as well as the introduction and spread of influenza A(H1N1)pdm09 in the country. Continuous influenza surveillance is needed to better understand the epidemiology of seasonal influenza and monitor the emergence of influenza strains with pandemic potential.