title: Long-term and seasonal dynamics of dengue in Iquitos, Peru.
abstract: BACKGROUND
  Long-term disease surveillance data provide a basis for studying drivers of pathogen transmission dynamics. Dengue is a mosquito-borne disease caused by four distinct, but related, viruses (DENV-1-4) that potentially affect over half the world's population. Dengue incidence varies seasonally and on longer time scales, presumably driven by the interaction of climate and host susceptibility. Precise understanding of dengue dynamics is constrained, however, by the relative paucity of laboratory-confirmed longitudinal data.
  
  
  METHODS
  We studied 10 years (2000-2010) of laboratory-confirmed, clinic-based surveillance data collected in Iquitos, Peru. We characterized inter and intra-annual patterns of dengue dynamics on a weekly time scale using wavelet analysis. We explored the relationships of case counts to climatic variables with cross-correlation maps on annual and trimester bases.
  
  
  RESULTS
  Transmission was dominated by single serotypes, first DENV-3 (2001-2007) then DENV-4 (2008-2010). After 2003, incidence fluctuated inter-annually with outbreaks usually occurring between October and April. We detected a strong positive autocorrelation in case counts at a lag of ∼ 70 weeks, indicating a shift in the timing of peak incidence year-to-year. All climatic variables showed modest seasonality and correlated weakly with the number of reported dengue cases across a range of time lags. Cases were reduced after citywide insecticide fumigation if conducted early in the transmission season.
  
  
  CONCLUSIONS
  Dengue case counts peaked seasonally despite limited intra-annual variation in climate conditions. Contrary to expectations for this mosquito-borne disease, no climatic variable considered exhibited a strong relationship with transmission. Vector control operations did, however, appear to have a significant impact on transmission some years. Our results indicate that a complicated interplay of factors underlie DENV transmission in contexts such as Iquitos.
authors.affiliation: Department of Entomology and Nematology, University of California, Davis, Davis, California, United States of America; Fogarty International Center, National Institutes of Health, Bethesda, Maryland, United States of America.
authors.forename: Steven T
authors.initials: ST
authors.lastname: Stoddard
authors.affiliation: University of New Mexico, Albuquerque, Albuquerque, New Mexico, United States of America.
authors.forename: Helen J
authors.initials: HJ
authors.lastname: Wearing
authors.affiliation: Department of Entomology and Nematology, University of California, Davis, Davis, California, United States of America; Fogarty International Center, National Institutes of Health, Bethesda, Maryland, United States of America.
authors.forename: Robert C
authors.initials: RC
authors.lastname: Reiner
authors.affiliation: Department of Entomology and Nematology, University of California, Davis, Davis, California, United States of America; U.S. Naval Medical Research Unit No. 6, Lima, Peru.
authors.forename: Amy C
authors.initials: AC
authors.lastname: Morrison
authors.affiliation: U.S. Naval Medical Research Unit No. 6, Lima, Peru.
authors.forename: Helvio
authors.initials: H
authors.lastname: Astete
authors.affiliation: U.S. Naval Medical Research Unit No. 6, Lima, Peru.
authors.forename: Stalin
authors.initials: S
authors.lastname: Vilcarromero
authors.affiliation: Loreto Regional Health Department, Iquitos, Peru.
authors.forename: Carlos
authors.initials: C
authors.lastname: Alvarez
authors.affiliation: Hospital Regional Iquitos, Iquitos, Peru.
authors.forename: Cesar
authors.initials: C
authors.lastname: Ramal-Asayag
authors.affiliation: Hospital Apoyo Iquitos, Iquitos, Peru.
authors.forename: Moises
authors.initials: M
authors.lastname: Sihuincha
authors.affiliation: U.S. Naval Medical Research Unit No. 6, Lima, Peru.
authors.forename: Claudio
authors.initials: C
authors.lastname: Rocha
authors.affiliation: U.S. Naval Medical Research Unit No. 6, Lima, Peru.
authors.forename: Eric S
authors.initials: ES
authors.lastname: Halsey
authors.affiliation: Department of Entomology and Nematology, University of California, Davis, Davis, California, United States of America; Fogarty International Center, National Institutes of Health, Bethesda, Maryland, United States of America.
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Scott
authors.affiliation: U.S. Naval Medical Research Center, Silver Spring, Maryland, United States of America.
authors.forename: Tadeusz J
authors.initials: TJ
authors.lastname: Kochel
authors.affiliation: U.S. Naval Medical Research Unit No. 6, Lima, Peru.
authors.forename: Brett M
authors.initials: BM
authors.lastname: Forshey
mesh_terms: D000818:Animals; D009033:Culicidae; D003715:Dengue / Q000453:epidemiology* / Q000635:transmission* / Q000821:virology*; D003716:Dengue Virus; D006801:Humans; D015994:Incidence; D010568:Peru / Q000453:epidemiology; D012621:Seasons; D014887:Weather