30 years of dengue fatal cases in Brazil: a laboratorial-based investigation of 1047 cases.

BACKGROUND: Dengue viruses (DENV) have emerged and reemerged in Brazil in the past 30 years causing explosive epidemics. The disease may range from clinically asymptomatic infections to severe and fatal outcomes. We aimed to describe the epidemiological, clinical and laboratorial aspects of the dengue fatal cases received by a Regional Reference Laboratory, Brazil in 30 years. METHODS: A total of 1047 suspected fatal dengue cases were received from 1986 to 2015 and analyzed in the Laboratory of Flavivirus, FIOCRUZ. Suspected cases were submitted to viral detection, serological and molecular methods for cases confirmation. Influence of gender, age, serotype and type of infection (primary/secondary) on death outcome, as well the interactions between serotype and age or infection and age and type of infection were also studied. RESULTS: A total of 359 cases (34.2%) were confirmed and DENV-1 (11.1%), DENV-2 (43.9%), DENV-3 (32.8%) and DENV-4 (13.7%) were detected. Overall, fatal cases occurred more often in primary infections (59.3%, p = 0.001). However, in 2008, fatal cases were mainly associated to secondary infections (p = 0.003). In 2008 and 2011, deaths were more frequent on children and those infected by DENV-2 presented a higher risk for fatal outcome. Moreover, children with secondary infections had a 4-fold higher risk for death. CONCLUSIONS: Dengue is a multifactorial disease and, factors such as viral strain/serotype, occurrence of secondary infections and co-morbidities may lead to a severe outcome. However, the high dengue incidence and transmission during epidemics, such as those observed in Brazil may overwhelm and collapse the public health services, potentially impacting on increased disease severity and mortality.

Evaluation of a generic RT-nested-PCR for detection of flaviviruses in suspected fatal cases of dengue infection, Rio de Janeiro, Brazil.

Flaviviruses are significant causes of disease worldwide and can be classified serologically into several antigenic complexes. The purpose of the present study was to evaluate the effectiveness of a generic RT-nested-PCR for detection of flavivirus during a dengue outbreak in Brazil in 2008. A total of 105 serum samples were collected from patients with fatal outcome and examined by generic RT-PCR, conventional RT-PCR, and IgM serology. The generic RT-PCR confirmed 19 of 105 (18%) cases. Conventional RT-PCR performed on 105 serum samples detected 45 (42.8%) dengue virus infections. The IgM serology confirmed 44 of 102 (43.1%) cases. The infecting serotype was identified by generic RT-PCR in 19 cases (18 DENV-2 and 1 DENV-3) and by conventional RT-PCR in 45 cases (40 DENV-2 and 5 DENV-3). In addition, we analyzed the performance of the generic and conventional RT-PCRs and IgM serology on serum samples stratified by the day of onset of symptoms. Our results indicate that different methods should be included in flavivirus surveillance programs, including virological and serological approaches.

Spatial evaluation and modeling of Dengue seroprevalence and vector density in Rio de Janeiro, Brazil.

BACKGROUND: 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.

Dengue virus type 3, Brazil, 2002.

During the summer of 2002, Rio de Janeiro had a large epidemic of dengue fever; 288,245 cases were reported. A subset of 1,831 dengue hemorrhagic fever cases occurred. In this study, performed in the first half of 2002, samples from 1,559 patients with suspected cases of dengue infection were analyzed. From this total, 1,497 were obtained from patients with nonfatal cases, and 62 were obtained from patients with fatal cases. By the use of different methods, 831 (53.3%) cases, including 40 fatal cases, were confirmed as dengue infection. When virus identification was successful, dengue virus type 3 (DENV-3) was obtained in 99% of cases. Neurologic involvement was shown in 1 patient with encephalitis, confirmed by the detection of DENV-3 RNA in the cerebrospinal fluid. This explosive epidemic of DENV-3 was the most severe dengue epidemic reported in Brazil since dengue viruses were introduced in 1986.