Human influenza surveillance in Cameroon: Differences in symptoms and seasonality by subtype

Between January 2010 and February of 2011, surveillance was conducted among patients with influenza-like illness (ILI). 1,837 patients of all ages presenting with ILI at 37 clinics and hospitals in 3 regions of Cameroon (Center, South and East) were included. Demographic information and symptoms were recorded for each patient. Participants provided either a nasopharyngeal or throat swab which was screened by real-time PCR for influenza viruses prior to virus isolation. Data was analyzed using STATA 11. As of February 2011, 98.2% of the samples have been tested. 17.8% were positive for influenza. 9.8% were Influenza B. H1N1 and H3N2 accounted for 5.7% and 2.4% of samples tested, respectively. 89.4% of influenza samples collected between March – September 2010 were Influenza B. 92.7% of flu samples collected between October 2010 – January 2011 were Influenza A viruses. Between November 2010 – January 2011, H1N1 accounted for 84.6% of the influenza positive samples for the 3 month period. 61.2% of influenza positives for September and October of 2010 were H3N2. Influenza B patients reported 27.3% more acute symptoms as compared to H3N2 patients and 16.7% more acute symptoms than H1N1 patients. This study points to seasonal trends of influenza by subtype in Cameroon. Continued surveillance is necessary to determine if this trend is observed annually, and surveillance should be expanded to include more regions of Cameroon. Some patients reported receiving influenza vaccine and presenting with ILI shortly thereafter. Research into the efficacy of the vaccine and subtypes circulating in Cameroon is imperative.