Laboratory Surveillance of Dengue in Rio Grande do Sul, Brazil, from 2007 to 2013

BackgroundAccording to official records, dengue was introduced in Brazil in the 80's; since then several epidemics have occurred. Meanwhile, in Rio Grande do Sul (RS, Southern Brazil) the first autochthonous case occurred only in 2007.Methodology and Principal FindingsIn this study we report laboratory surveillance of dengue cases and seasonality of positive cases, describe serotypes and characterize the epidemiological pattern of dengue in RS from 2007 to 2013. A total of 9,779 serum samples from patients with suspected dengue fever were collected and submitted to molecular and/or serological analyses for dengue virus identification and serotyping, based on viral isolation, NS1 antigen detection and qRT-PCR, or Dengue IgM capture ELISA and MAC-ELISA. The first autochthonous dengue case in RS was confirmed in 2007 (DENV-3). While in 2008 and 2009 only imported cases were registered, autochthonous infection waves have been occurring since 2010. The highest number of dengue infections occurred in 2010, with DENV-1 and DENV-2 outbreaks in Northwestern RS. In 2011, another DENV-1 and DENV-2 outbreak occurred in the Northwestern region; moreover, DENV-4 was detected in travelers. In 2012, DENV-1 and DENV-4 co-circulated. DENV-2 circulation was only detected again in 2013, in high frequency (56.7%), co-circulating with DENV-4 (35%). Most infections occur in adults during summer. Differences in prevalence between genders were observed in 2007 (60% females), 2008 (60.8% males) and 2009 (77.5% males).ConclusionsAccording to results of dengue surveillance, there was an increase in the number of dengue cases in RS and of cities infested with Aedes aegypti, possibly as a consequence of introduction of new serotypes and the difficulty of health programs to control the vector.研究背景：据官方记录，登革热于20世纪80年代传入巴西，自此当地先后暴发多起登革热疫情。巴西南部的南里奥格兰德州（Rio Grande do Sul，简称RS）直至2007年才报告首例本地感染病例（autochthonous case）。 研究方法与主要结果：本研究针对2007至2013年RS州的登革热病例开展实验室监测与阳性病例的季节分布特征分析，描述登革病毒血清型分布，并阐明该地区登革热的流行病学模式。研究共收集9779份疑似登革热患者的血清样本，通过病毒分离、NS1抗原检测、实时荧光定量反转录聚合酶链反应（qRT-PCR），或登革病毒IgM捕获酶联免疫吸附试验（Dengue IgM capture ELISA）、微量酶联免疫吸附试验（MAC-ELISA）开展分子及/或血清学检测，以鉴定登革病毒并完成血清分型。 2007年，RS州确认首例本地感染登革热病例，其血清型为登革病毒3型（DENV-3）。2008年与2009年仅报告输入性病例，自2010年起该地区陆续出现本地感染流行波。2010年为登革热感染人数最多的年份，RS州西北部暴发登革病毒1型（DENV-1）与登革病毒2型（DENV-2）联合疫情。2011年，该州西北部再次暴发DENV-1与DENV-2疫情；此外，在旅行者中检出登革病毒4型（DENV-4）。2012年，DENV-1与DENV-4共同流行。直至2013年才再次检出DENV-2流行，其检出频率高达56.7%，并与DENV-4（35%）共同循环传播。大多数登革热感染发生于夏季的成年人群中。2007年（女性占比60%）、2008年（男性占比60.8%）与2009年（男性占比77.5%）均观察到不同性别间的感染率差异。 研究结论：登革热监测结果显示，RS州的登革热病例数与埃及伊蚊（Aedes aegypti）孳生的城市数量均有所增加，这可能与新型登革病毒血清型的传入以及卫生防控项目难以有效控制媒介昆虫有关。