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An Investigation of a Major Outbreak of Rift Valley Fever in Kenya: 2006–2007

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  • Kenya Ministry of Public Health and Sanitation, Nairobi, Kenya; Field Epidemiology and Laboratory Training Program, Nairobi, Kenya; Provincial Medical Office, Garissa, Kenya; Epidemic Intelligence Service, Office of Workforce and Career Development, Centers for Disease Control and Prevention (CDC), Atlanta, Georgia; Division of Vector-Borne Infectious Diseases, National Center for Zoonotic, Vector-Borne, and Enteric Diseases, CDC, Fort Collins, Colorado; Centre for Virologic Research, Kenya Medical Research Institute, Nairobi, Kenya; United States Army Medical Research Unit-Kenya, Nairobi, Kenya; Global Disease Detection Division, CDC-Kenya, Nairobi, Kenya

An outbreak of Rift Valley fever (RVF) occurred in Kenya during November 2006 through March 2007. We characterized the magnitude of the outbreak through disease surveillance and serosurveys, and investigated contributing factors to enhance strategies for forecasting to prevent or minimize the impact of future outbreaks. Of 700 suspected cases, 392 met probable or confirmed case definitions; demographic data were available for 340 (87%), including 90 (26.4%) deaths. Male cases were more likely to die than females, Case Fatality Rate Ratio 1.8 (95% Confidence Interval [CI] 1.3–3.8). Serosurveys suggested an attack rate up to 13% of residents in heavily affected areas. Genetic sequencing showed high homology among viruses from this and earlier RVF outbreaks. Case areas were more likely than non-case areas to have soil types that retain surface moisture. The outbreak had a devastatingly high case-fatality rate for hospitalized patients. However, there were up to 180,000 infected mildly ill or asymptomatic people within highly affected areas. Soil type data may add specificity to climate-based forecasting models for RVF.

Author Notes

*Address correspondence to Robert F. Breiman, Global Disease Detection Division, CDC-Kenya, Mbagathi Road, Off Mbagathi Way, Nairobi, Kenya. E-mail: rbreiman@ke.cdc.gov

Authors' addresses: Patrick M. Nguku, Division of Communicable Disease Control, Ministry of Public Health and Sanitation, Nairobi, Kenya, E-mail: drnguku@yahoo.com. Shahnaaz K. Shariff, Director of Public Health and Sanitation, Ministry of Public Health and Sanitation, Nairobi, Kenya, E-mails: sksharif@africaonline.co.ke or pphs@health.go.ke. David Mutonga, Head, Division of Disease Surveillance and Response, Ministry of Health, Nairobi, Kenya, E-mail: davidmutonga@yahoo.com. Amwayi Samuel Anyangu, Ministry of Public Health and Sanitation, Department of Disease Prevention and Control, Field Epidemiology and Laboratory Training Program (FELTP), Epi Track Field Coordinator, Nairobi, Kenya, E-mail: amwayi2004@yahoo.com. Jared O. Omolo, Program Coordinator, Field Epidemiology and Laboratory Training Program, Ministry of Public Health and Sanitation, Nairobi, Kenya, E-mail: jaredom2000@yahoo.com. Eileen Farnon, Division of Parasitic Diseases, Centers for Disease Control and Prevention, Atlanta, GA, E-mail: edf6@cdc.gov. Hannah L. Gould, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, GA, E-mail: dvj9@cdc.gov. Edith R. Lederman, Infectious Disease Clinical Research Program (IDCRP), Naval Medical Center, San Diego, CA, E-mail: edith.lederman@med.navy.mil. Carol Y. Rao, International Emerging Infections Program, CDC-China, Beijing, China, E-mails: cnr3@cdc.gov. Rosemary Sang, Kenya Medical Research Institute (KEMRI), Nairobi, Kenya, E-mails: Rsang@wrp-nbo.org or Rsang@kemri.org. David Schnabel, US Army Medical Research Unit – Kenya, E-mail: dschnabel@wrp-nbo.org. Daniel Feikin, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, E-mail: dfeikin@jhsph.edu. Allen Hightower, Division of Parasitic Diseases, Centers for Disease Control and Prevention, Atlanta, GA, E-mail: awh1@cdc.gov. M. Kariuki Njenga, International Emerging Infections Program, CDC-Kenya, KEMRI Headquarters, Nairobi, Kenya, E-mail: KNjenga@ke.cdc.gov. Robert F. Breiman, Office of the Director, CDC-Kenya, KEMRI Headquarters, Nairobi, Kenya, E-mail: RBreiman@ke.cdc.gov.

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