Figure 1.

Monthly occurrence of diagnosed dengue fever cases in Iquitos, Peru, during 2006–2010. The period during which dengue virus serotype 3 (DENV-3) transmission was predominant is denoted by green bars, and the period during which DENV-4 transmission was predominant is denoted by purple bars. The timing of each longitudinal cohort (A and B) is shown at the top of the figure; during the DENV-4 period, they overlap. Cases were detected by active community-based surveillance for febrile illness and confirmed in the laboratory. When virus was isolated, the infecting serotype is shown; otherwise, cases positive for immunoglobulin M antibody are denoted as “DENV.”