Results from the first six years of national sentinel surveillance for influenza in Kenya, July 2007-June 2013.

Mark A Katz,Lilian W Waiboci,Jamal A Ahmed,Rosalia Kalani,Robert F Breiman,Daniel R Feikin,Gideon O Emukule,Moses K Njenga,Godfrey Bigogo,Joshua A Mott,Philip Muthoka,Henry Njuguna,Baochuan Lin

doi:10.1371/journal.pone.0098615

Abstract

BackgroundRecent studies have shown that influenza is associated with significant disease burden in many countries in the tropics, but until recently national surveillance for influenza was not conducted in most countries in Africa.MethodsIn 2007, the Kenyan Ministry of Health with technical support from the CDC-Kenya established a national sentinel surveillance system for influenza. At 11 hospitals, for every hospitalized patient with severe acute respiratory illness (SARI), and for the first three outpatients with influenza-like illness (ILI) per day, we collected both nasopharyngeal and oropharyngeal swabs. Beginning in 2008, we conducted in-hospital follow-up for SARI patients to determine outcome. Specimens were tested by real time RT-PCR for influenza A and B. Influenza A-positive specimens were subtyped for H1, H3, H5, and (beginning in May 2009) A(H1N1)pdm09.ResultsFrom July 1, 2007 through June 30, 2013, we collected specimens from 24,762 SARI and 14,013 ILI patients. For SARI and ILI case-patients, the median ages were 12 months and 16 months, respectively, and 44% and 47% were female. In all, 2,378 (9.6%) SARI cases and 2,041 (14.6%) ILI cases were positive for influenza viruses. Most influenza-associated SARI cases (58.6%) were in children <2 years old. Of all influenza-positive specimens, 78% were influenza A, 21% were influenza B, and 1% were influenza A/B coinfections. Influenza circulated in every month. In four of the six years influenza activity peaked during July–November. Of 9,419 SARI patients, 2.7% died; the median length of hospitalization was 4 days.ConclusionsDuring six years of surveillance in Kenya, influenza was associated with nearly 10 percent of hospitalized SARI cases and one-sixth of outpatient ILI cases. Most influenza-associated SARI and ILI cases were in children <2 years old; interventions to reduce the burden of influenza, such as vaccine, could consider young children as a priority group.

Highlights

Influenza causes substantial morbidity and mortality worldwide every year
During six years of surveillance in Kenya, influenza was associated with nearly 10 percent of hospitalized severe acute respiratory illness (SARI) cases and one-sixth of outpatient influenza-like illness (ILI) cases
Most influenza-associated SARI and ILI cases were in children,2 years old; interventions to reduce the burden of influenza, such as vaccine, could consider young children as a priority group

Summary

Introduction

Influenza causes substantial morbidity and mortality worldwide every year. While seasonal influenza has long been recognized as a cause of morbidity and mortality in developed countries with temperate climates, recent studies have shown that influenza causes a significant burden of disease in countries throughout the tropics as well [2,3,4]. A number of countries in Africa were able to use public health resources to improve their capacity to conduct virological and epidemiological surveillance for influenza [10,11]. Recent studies have shown that influenza is associated with significant disease burden in many countries in the tropics, but until recently national surveillance for influenza was not conducted in most countries in Africa

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