A prospective, multicentre, cohort study to assess the incidence of dengue illness in households from selected communities in Brazil (2014–2018)

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OBJECTIVES: To estimate the incidence of dengue infection across geographically distinct areas of Brazil. METHODS: This prospective, household-based, cohort study enrolled participants in five areas and followed them up for up to 4 years (2014-2018). Dengue seroprevalence was assessed at each scheduled visit. Suspected dengue cases were identified through enhanced passive and active surveillance. Acute symptomatic dengue infection was confirmed through reverse-transcriptase quantitative polymerase chain reaction in combination with an antigenic assay (non-structural protein 1) and serology. RESULTS: Among 3300 participants enrolled, baseline seroprevalence was 76.2%, although only 23.3% of participants reported a history of dengue. Of 1284 suspected symptomatic dengue cases detected, 50 (3.9%) were laboratory-confirmed. Based on 8166.5 person-years (PY) of follow-up, the incidence of laboratory-confirmed symptomatic infection (primary endpoint) was 6.1 per 1000 PY (95% confidence interval [CI]: 4.5, 8.1). Incidence varied substantially in different years (1.8-7.4 per 1000 PY). The incidence of inapparent primary dengue infection was substantially higher: 41.7 per 1000 PY (95% CI: 31.1, 54.6). CONCLUSIONS: Our findings, highlighting that the incidence of dengue infection is underestimated in Brazil, will inform the design and implementation of future dengue vaccine trials. CLINICAL TRIAL REGISTRATION: NCT01751139.