title: Spatial and temporal pattern of Rift Valley fever outbreaks in Tanzania; 1930 to 2007.
abstract: BACKGROUND
  Rift Valley fever (RVF)-like disease was first reported in Tanzania more than eight decades ago and the last large outbreak of the disease occurred in 2006-07. This study investigates the spatial and temporal pattern of RVF outbreaks in Tanzania over the past 80 years in order to guide prevention and control strategies.
  
  
  METHODS
  A retrospective study was carried out based on disease reporting data from Tanzania at district or village level. The data were sourced from the Ministries responsible for livestock and human health, Tanzania Meteorological Agency and research institutions involved in RVF surveillance and diagnosis. The spatial distribution of outbreaks was mapped using ArcGIS 10. The space-time permutation model was applied to identify clusters of cases, and a multivariable logistic regression model was used to identify risk factors associated with the occurrence of outbreaks in the district.
  
  
  RESULTS
  RVF outbreaks were reported between December and June in 1930, 1947, 1957, 1960, 1963, 1968, 1977-79, 1989, 1997-98 and 2006-07 in 39.2% of the districts in Tanzania. There was statistically significant spatio-temporal clustering of outbreaks. RVF occurrence was associated with the eastern Rift Valley ecosystem (OR = 6.14, CI: 1.96, 19.28), total amount of rainfall of >405.4 mm (OR = 12.36, CI: 3.06, 49.88), soil texture (clay [OR = 8.76, CI: 2.52, 30.50], and loam [OR = 8.79, CI: 2.04, 37.82]).
  
  
  CONCLUSIONS
  RVF outbreaks were found to be distributed heterogeneously and transmission dynamics appeared to vary between areas. The sequence of outbreak waves, continuously cover more parts of the country. Whenever infection has been introduced into an area, it is likely to be involved in future outbreaks. The cases were more likely to be reported from the eastern Rift Valley than from the western Rift Valley ecosystem and from areas with clay and loam rather than sandy soil texture.
authors.affiliation: National Institute for Medical Research, Tabora, Tanzania ; Department of Veterinary Medicine and Public Health, Sokoine University of Agriculture, Morogoro, Tanzania ; Southern Africa Centre for Infectious Disease Surveillance, Morogoro, Tanzania.
authors.forename: Calvin
authors.initials: C
authors.lastname: Sindato
authors.affiliation: Department of Veterinary Medicine and Public Health, Sokoine University of Agriculture, Morogoro, Tanzania ; Southern Africa Centre for Infectious Disease Surveillance, Morogoro, Tanzania.
authors.forename: Esron D
authors.initials: ED
authors.lastname: Karimuribo
authors.affiliation: Royal Veterinary College, London, United Kingdom.
authors.forename: Dirk U
authors.initials: DU
authors.lastname: Pfeiffer
authors.affiliation: National Institute for Medical Research, Dar es Salaam, Tanzania.
authors.forename: Leonard E G
authors.initials: LE
authors.lastname: Mboera
authors.affiliation: Food and Agriculture Organization of the United Nations, Dar es Salaam, Tanzania.
authors.forename: Fredrick
authors.initials: F
authors.lastname: Kivaria
authors.affiliation: Department of Disease Control, University of Zambia, Lusaka, Zambia.
authors.forename: George
authors.initials: G
authors.lastname: Dautu
authors.affiliation: International Livestock Research Institute, Nairobi, Kenya.
authors.forename: Bett
authors.initials: B
authors.lastname: Bernard
authors.affiliation: Center for Emerging and Zoonotic Diseases, National Institute for Communicable Diseases, of the National Health Laboratory Service, Sandringham, South Africa ; School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa.
authors.forename: Janusz T
authors.initials: JT
authors.lastname: Paweska
mesh_terms: D000820:Animal Diseases / Q000453:epidemiology*; D000818:Animals; D002417:Cattle / Q000821:virology; D004196:Disease Outbreaks; D006041:Goats / Q000821:virology; D006801:Humans; D058751:Livestock / Q000821:virology; D012189:Retrospective Studies; D012295:Rift Valley Fever / Q000453:epidemiology* / Q000821:virology; D012296:Rift Valley fever virus; D012756:Sheep / Q000821:virology; D013636:Tanzania / Q000453:epidemiology