Laboratório de Transmissores de Hematozoários, Instituto Oswaldo Cruz, Fiocruz, Rio de Janeiro, Brasil.
PLoS Negl Trop Dis. 2009 Nov 10;3(11):e545. doi: 10.1371/journal.pntd.0000545.
Rio de Janeiro, Brazil, experienced a severe dengue fever epidemic in 2008. This was the worst epidemic ever, characterized by a sharp increase in case-fatality rate, mainly among younger individuals. A combination of factors, such as climate, mosquito abundance, buildup of the susceptible population, or viral evolution, could explain the severity of this epidemic. The main objective of this study is to model the spatial patterns of dengue seroprevalence in three neighborhoods with different socioeconomic profiles in Rio de Janeiro. As blood sampling coincided with the peak of dengue transmission, we were also able to identify recent dengue infections and visually relate them to Aedes aegypti spatial distribution abundance. We analyzed individual and spatial factors associated with seroprevalence using Generalized Additive Model (GAM).
METHODOLOGY/PRINCIPAL FINDINGS: Three neighborhoods were investigated: a central urban neighborhood, and two isolated areas characterized as a slum and a suburban area. Weekly mosquito collections started in September 2006 and continued until March 2008. In each study area, 40 adult traps and 40 egg traps were installed in a random sample of premises, and two infestation indexes calculated: mean adult density and mean egg density. Sera from individuals living in the three neighborhoods were collected before the 2008 epidemic (July through November 2007) and during the epidemic (February through April 2008). Sera were tested for DENV-reactive IgM, IgG, Nested RT-PCR, and Real Time RT-PCR. From the before-after epidemics paired data, we described seroprevalence, recent dengue infections (asymptomatic or not), and seroconversion. Recent dengue infection varied from 1.3% to 14.1% among study areas. The highest IgM seropositivity occurred in the slum, where mosquito abundance was the lowest, but household conditions were the best for promoting contact between hosts and vectors. By fitting spatial GAM we found dengue seroprevalence hotspots located at the entrances of the two isolated communities, which are commercial activity areas with high human movement. No association between recent dengue infection and household's high mosquito abundance was observed in this sample.
CONCLUSIONS/SIGNIFICANCE: This study contributes to better understanding the dynamics of dengue in Rio de Janeiro by assessing the relationship between dengue seroprevalence, recent dengue infection, and vector density. In conclusion, the variation in spatial seroprevalence patterns inside the neighborhoods, with significantly higher risk patches close to the areas with large human movement, suggests that humans may be responsible for virus inflow to small neighborhoods in Rio de Janeiro. Surveillance guidelines should be further discussed, considering these findings, particularly the spatial patterns for both human and mosquito populations.
巴西里约热内卢在 2008 年经历了一场严重的登革热疫情。这是有史以来最严重的一次疫情，其特点是病死率急剧上升，主要发生在年轻人中。气候、蚊子数量、易感人群的积累或病毒进化等多种因素都可能解释这次疫情的严重程度。本研究的主要目的是对里约热内卢三个具有不同社会经济特征的街区的登革热血清流行率的空间模式进行建模。由于血液采样恰逢登革热传播的高峰期，我们还能够识别出最近的登革热感染，并将其与埃及伊蚊的空间分布丰度进行直观的关联。我们使用广义加性模型（GAM）分析了与血清流行率相关的个体和空间因素。
方法/主要发现：研究了三个街区：一个中心城市街区和两个隔离区，分别是一个贫民窟和一个郊区。每周的蚊子收集工作于 2006 年 9 月开始，一直持续到 2008 年 3 月。在每个研究区域，在随机选择的场所中安装了 40 个成人诱捕器和 40 个卵诱捕器，并计算了两个滋生指数：平均成虫密度和平均卵密度。在 2008 年疫情（2007 年 7 月至 11 月）之前和疫情期间（2008 年 2 月至 4 月），从居住在这三个街区的个体中采集血清。对血清进行检测，以确定是否存在 DENV 反应性 IgM、IgG、巢式 RT-PCR 和实时 RT-PCR。从疫情前后配对数据中，我们描述了血清流行率、近期登革热感染（有无症状）和血清转化率。在研究区域中，最近的登革热感染率从 1.3%到 14.1%不等。在贫民窟中，IgM 血清阳性率最高，那里蚊子的数量最少，但家庭条件最有利于促进宿主和媒介之间的接触。通过拟合空间 GAM，我们发现登革热血清流行率的热点位于两个隔离社区的入口处，这些地区是商业活动区，人流量大。在这个样本中，没有观察到近期登革热感染与家庭蚊子大量滋生之间的关联。
结论/意义：本研究通过评估登革热血清流行率、近期登革热感染和媒介密度之间的关系，有助于更好地了解里约热内卢的登革热动态。总之，街区内空间血清流行率模式的变化，在靠近人流量大的区域存在明显的高风险斑块，这表明人类可能是导致里约热内卢小街区病毒流入的原因。监测指南应进一步讨论，特别是考虑到人类和蚊子种群的空间模式。
