Estudo da tríplice epidemia de Zika, Dengue e Chikungunya em Feira de Santana – Bahia.

Abstract

Introduction: The emergence and re-emergence of infectious agents transmitted by vector mosquitoes has been a major challenge for Global Public Health and, in particular, for Brazil. This country, after the re-emergence of dengue virus (DENV), started to present successive epidemics of great magnitude of this virus since 1986. Since the second semester of 2014, with the emergence of the chikungunya (CHIKV) and Zika (ZIKV) viruses, the simultaneous circulation of these three arboviruses in intra-urban spaces was established, outlining an epidemiological situation never recorded in the western world. This thesis aimed to investigate epidemiological characteristics of the simultaneous circulation of Zika, dengue and chikungunya viruses in a large urban center. Article I – Objective: To estimate the seroprevalence of CHIKV in different countries. Methods: It was carried out a systematic review of articles published until 2020 in Medline/Pubmed, Embase, Lilacs and Web of Science. Cross-sectional, cohort and case- control studies were included, which presented previous or previous and recent laboratory confirmation of infection and those conducted with symptomatic participants were excluded. Results: A total of 596 articles were identified, 197 were read in full and 64 were included in the analysis, from which 71 seroprevalence studies were extracted, as some had more than one studied population. Most studies were cross-sectional (92%), conducted between 2001 and 2020 (92%), with population of all ages (55%), in Kenya, Brazil and French Polynesia. The estimated seroprevalences were 24% (95%CI 19-29; I2=99.7%; p<0.00), with 21% (95%CI 13-30; I2=99.5%; p<0.00) in adults, 7% (95%CI 0-23; I2=99.7%; p<0.00) in children and 30% (95%CI 23-38; I2=99.7%; p<0.00) in all ages. The highest seroprevalences were found in African and Americas Regions. Article II – Objective: To estimate the seroprevalence of CHIKV infection in a large urban center and to investigate the relation between viral circulation and living conditions. Methods: A population-based ecological study was conducted in 30 Sentinel Areas of Feira de Santana, through household interviews and a serological survey between 2016 and 2017. Participants had a venous blood sample collected to perform the chikungunya IgM and IgG serological tests. Results: 1,981 participants were randomly selected from the 16,620 respondents. The seroprevalence found was 22.1% and ranged from 2.0% to 70.5% among the Sentinel Areas. Seroprevalence was significantly lower in areas with high living conditions when compared to areas with low living conditions. A correlation was found between CHIKV seroprevalence and population density (r=0.24; p=0.02). Article III – Objective: to analyze the spatial diffusion of the simultaneous circulation of three arboviruses, transmitted by the same vector, in a large urban center, over two epidemic waves in two consecutive years. Methods: An ecological study of spatial and temporal aggregates on the occurrence of dengue, chikungunya, and Zika, from 2014 to 2019, in Feira de Santana, Bahia State, was carried out using data of cases reported to the national surveillance system. Four different methods were used to analyze the spatial diffusion: Kernel Estimation with sequential maps, cumulative nearest-neighbor ratios (NNI) over time, spatial correlograms and local autocorrelation changes (LISA) over time. Results: From 2014-2019, there were 21,723 confirmed cases of arboviruses. The highest incidences were among women (496.9, 220.2, and 91.0 cases/100,000 women for dengue, chikungunya and Zika respectively). By age group, the highest incidences were from ages 10-19 years old (609.3 dengue cases/100,000), from 60 and more (306.7 chikungunya cases/100,000), and from 0-9 years old (124.1 Zika cases / 100,000 inhabitants). The temporal distribution demonstrated two epidemic waves of simultaneous circulation in 2014 and 2015. The spatial methods evidenced that dengue, chikungunya and Zika presented expansion pattern of difusion in Feira de Santana. Conclusions of the Thesis: A great heterogeneity of CHIKV seroprevalence was observed among different countries and intra-urban populations, possibly resulting from the complexity of the factors involved in the modulation of the transmission of this arbovirus. Among them, the time of virus circulation, population susceptibility, absence of effective vaccines, availability of breeding sites and high population density. This diversity of factors, as well as the lack of effective measures to control its main vector, led to the alarming epidemiological scenario in Feira de Santana. In this urban center, the climatic and socioeconomic conditions of the population were extremely receptive to the introduction and rapid circulation of CHIKV and ZIKV, where DENV was already circulating in an endemic andepidemic way. The sum of these factors contributed to these arboviruses continuing to constitute important public health concerns.