Epidemiology of 2009 Pandemic Influenza A Virus Subtype H1N1 Among Kenyans Aged 2 Months to 18 Years, 2009–2010

Background. The US Army Medical Research Unit –Kenya (USAMRU-K) conducts surveillance for influenza-like illness (ILI) in Kenya. We describe the temporal and geographic progression of A(H1N1)pdm09 as it emergedin Kenya and characterize the outpatient population with A(H1N1)pdm09 infection.Methods. We included patients with ILI aged 2 months to 18 years enrolled during June 2009–August 2010.Respiratory specimens were tested by real-time reverse-transcription polymerase chain reaction for influenza virus.Patients with A(H1N1)pdm09 infection were compared to those with seasonal influenza A virus infection and thosewith ILI who had no virus or a virus other than influenza virus identified (hereafter, “noninfluenza ILI”).Results. Of 4251 patients with ILI, 193 had laboratory-confirmed A(H1N1)pdm09 infection. The first pandemicinfluenza case detected by USAMRU-K surveillance was in August 2009; peak activity nationwide occurred duringOctober–November 2009. Patients with A(H1N1)pdm09 infection were more likely to be school-aged, comparedwith patients with seasonal influenza A virus infection (prevalence ratio [PR], 2.0; 95% confidence interval [CI],1.3–3.1) or noninfluenza ILI (PR, 3.2; 95% CI, 2.4–4.3).Conclusions . USAMRU-K ILI surveillance detected the geographic and temporal distribution of pandemic influ-enza in Kenya. The age distribution of A(H1N1)pdm09 infections included more school-aged children, comparedwith seasonal influenza Avirus infection and noninfluenza ILI.In March and April 2009, 2009 pandemic influenza Avirus subtype H1N1 (A[H1N1]pdm09) emerged inMexico and the United States [1, 2]. The strain spreadrapidly worldwide, and on 11 June 2009, the WorldHealth Organization declared the start of the pandem-ic phase [3]. In Kenya, A(H1N1)pdm09 was firstidentified on 29 June 2009 and was traced to 4 parallelintroductions of the virus to Nairobi from the UnitedKingdom [4].Little has been published about the epidemiology ofA(H1N1)pdm09 in Africa [5]. Understanding theemergence and spread of the pandemic across the geo-graphically diverse regions of Kenya is important forfuture pandemic preparedness. We describe the emer-gence of A(H1N1)pdm09 in Kenya among children,as detected by the US Army Medical Research Unit–Kenya (USAMRU-K) outpatient ILI surveillancenetwork, and compare the characteristics of patientswith A(H1N1)pdm09 infection to those of patientswith seasonal influenza A virus infection and thosewith ILI who had no virus or a virus other than influ-enza virus identified (hereafter, noninfluenza ILI).