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.
Materials and 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.
Principal Findings: 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]).
Conclusion/Significance: 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.
