Epidemiological characteristics and determinants of dengue transmission during epidemic and non-epidemic years in Fortaleza, Brazil: 2011-2015

BackgroundAfter being eliminated during the 1950s, dengue reemerged in Brazil in the 1980s. Since then, incidence of the disease has increased, as serotypes move within and between cities. The co-circulation of multiple serotypes contributes to cycles of epidemic and interepidemic years, and a seasonal pattern of transmission is observed annually. Little is known regarding possible differences in the epidemiology of dengue under epidemic and interepidemic scenarios. This study addresses this gap and aims to assess the epidemiological characteristics and determinants of epidemic and interepidemic dengue transmission, utilizing data from the 5th largest city in Brazil (Fortaleza), at fine spatial and temporal scales.Methods/Principal findingsLongitudinal models of monthly rates of confirmed dengue cases were used to estimate the differential contribution of contextual factors to dengue transmission in Fortaleza between 2011 and 2015. Models were stratified by annual climatological schedules and periods of interepidemic and epidemic transmission, controlling for social, economic, structural, entomological, and environmental factors. Results revealed distinct seasonal patterns between interepidemic and epidemic years, with persistent transmission after June in interepidemic years. Dengue was strongly associated with violence across strata, and with poverty and irregular garbage collection during periods of low transmission, but not with other indicators of public service provision or structural deprivation. Scrapyards and sites associated with tire storage were linked to incidence differentially between seasons, with the strongest associations during transitional precipitation periods. Hierarchical clustering analysis suggests that the dengue burden concentrates in the southern periphery of the city, particularly during periods of minimal transmission.Conclusions/SignificanceOur findings have direct programmatic implications. Vector control operations must be sustained after June even in non-epidemic years. More specifically, scrapyards and sites associated with tires (strongly associated with incidence during periods of minimal transmission), require sustained entomological surveillance, particularly during interepidemic intervals and in the urban periphery. Intersectoral collaborations that address urban violence are critical for facilitating the regular activities of vector control agents.背景：登革热曾于1950年代在巴西被消灭，后于1980年代重现。自此之后，随着登革热血清型在城市内部及城市间传播扩散，该病发病率持续上升。多种血清型的共同循环促成了流行年与间歇流行年的周期波动，且每年均呈现固定的季节性传播模式。目前学界对流行年与间歇流行年登革热流行病学特征的差异仍知之甚少。本研究旨在填补这一研究空白，以巴西第五大城市福塔莱萨（Fortaleza）的精细化时空尺度数据为基础，评估流行与间歇流行场景下登革热传播的流行病学特征及影响因素。 研究方法与主要发现：本研究采用2011至2015年登革热确诊病例月度发病率的纵向模型，估算福塔莱萨地区登革热传播中各类背景因素的差异化贡献。模型按年度气候周期、间歇流行与流行传播时段进行分层，并控制了社会、经济、结构、媒介生物学及环境相关混杂因素。结果显示，间歇流行年与流行年的季节性传播模式存在显著差异：间歇流行年在6月后仍存在持续的病毒传播。登革热发病与各分层的暴力事件显著相关，在低传播时段则与贫困及垃圾清运不规范密切相关，但与其他公共服务供给指标或结构性匮乏无显著关联。废车场及轮胎储存相关场所与发病率的关联随季节呈现差异，在降水过渡期的关联强度最高。层级聚类分析结果表明，登革热疾病负担集中在城市南部郊区，尤其在低传播时段更为显著。 结论与意义：本研究结果具有直接的公共卫生项目应用价值。即便在非流行年，6月后仍需持续开展媒介伊蚊防控工作。具体而言，废车场及轮胎储存相关场所（在低传播时段与发病关联极强）需要开展持续的媒介生物学监测，尤其在间歇流行时段及城市郊区。针对城市暴力问题的跨部门协作，对保障媒介防控人员的日常工作开展至关重要。