National burden of hospitalized and non-hospitalized influenza-associated severe acute respiratory illness in Kenya, 2012-2014.

BACKGROUND: Influenza-associated respiratory illness was substantial during the emergence of the 2009 influenza pandemic. Estimates of influenza burden in the post-pandemic period are unavailable to guide Kenyan vaccine policy. OBJECTIVES: To update estimates of hospitalized and non-hospitalized influenza-associated severe acute respiratory illness (SARI) during a post-pandemic period (2012-2014) and describe the incidence of disease by narrow age categories. METHODS: We used data from Siaya County Referral Hospital to estimate age-specific base rates of SARI. We extrapolated these base rates to other regions within the country by adjusting for regional risk factors for acute respiratory illness (ARI), regional healthcare utilization for acute respiratory illness, and the proportion of influenza-positive SARI cases in each region, so as to obtain region-specific rates. RESULTS: The mean annual rate of hospitalized influenza-associated SARI among all ages was 21 (95% CI 19-23) per 100 000 persons. Rates of non-hospitalized influenza-associated SARI were approximately 4 times higher at 82 (95% CI 74-90) per 100 000 persons. Mean annual rates of influenza-associated SARI were highest in children <2 years of age with annual hospitalization rates of 147 (95% CI of 134-160) per 100 000 persons and non-hospitalization rates of 469 (95% CI 426-517) per 100 000 persons. For the period 2012-2014, there were between 8153 and 9751 cases of hospitalized influenza-associated SARI and 31 785-38 546 cases of non-hospitalized influenza-associated SARI per year. CONCLUSIONS: The highest burden of disease was observed among children <2 years of age. This highlights the need for strategies to prevent influenza infections in this age group.