High Zika Virus Seroprevalence in Salvador, Northeastern Brazil Limits the Potential for Further Outbreaks

Abstract

During 2015 to 2016, Brazil reported more Zika virus (ZIKV) cases than any other country, yet population exposure remains unknown. Serological studies of ZIKV are hampered by cross-reactive immune responses against heterologous viruses. We conducted serosurveys for ZIKV, dengue virus (DENV), and Chikungunya virus (CHIKV) in 633 individuals prospectively sampled during 2015 to 2016, including microcephaly and non-microcephaly pregnancies, HIV-infected patients, tuberculosis patients, and university staff in Salvador in northeastern Brazil using enzyme-linked immunosorbent assays (ELISAs) and plaque reduction neutralization tests. Sera sampled retrospectively during 2013 to 2015 from 277 HIV-infected patients were used to assess the spread of ZIKV over time. Individuals were georeferenced, and sociodemographic indicators were compared between ZIKV-positive and -negative areas and areas with and without microcephaly cases. Epidemiological key parameters were modeled in a Bayesian framework. ZIKV seroprevalence increased rapidly during 2015 to 2016, reaching 63.3% by 2016 (95% confidence interval [CI], 59.4 to 66.8%), comparable to the seroprevalence of DENV (75.7%; CI, 69.4 to 81.1%) and higher than that of CHIKV (7.4%; CI, 5.6 to 9.8%). Of 19 microcephaly pregnancies, 94.7% showed ZIKV IgG antibodies, compared to 69.3% of 257 non-microcephaly pregnancies (P = 0.017). Analyses of sociodemographic data revealed a higher ZIKV burden in low socioeconomic status (SES) areas. High seroprevalence, combined with case data dynamics allowed estimates of the basic reproduction number R0 of 2.1 (CI, 1.8 to 2.5) at the onset of the outbreak and an effective reproductive number Reff of <1 in subsequent years. Our data corroborate ZIKV-associated congenital disease and an association of low SES and ZIKV infection and suggest that population immunity caused cessation of the outbreak. Similar studies from other areas will be required to determine the fate of the American ZIKV outbreak.

Inferring the ecological drivers of arboviral outbreaks

“…These reporting rates were in stark contrast to estimated Zika reporting rates of 16% and 18% in El Salvador and Suriname, respectively (Shutt et al, 2017), but in agreement with observation rates of 2.7% in Cabo Verde Islands, West Africa (Lourenço et al, 2018). High seroprevalence levels of over 50% were also agreed with previous cross-sectional serological studies in Salvador, Brazil (Netto et al, 2017), Yap Island (Duffy et al, 2009), French…”

Epidemiology of acute febrile illness in Latin America

“…Due to its clinical and epidemiological importance [7], DENV has been the most studied AFI aetiology and was the most prevalent cause of diseases in our review. However, recent studies have demonstrated displacement of DENV by ZIKV and CHIKV, or a concurrent circulation of all three arboviruses in the same place [19,23,59]. From a clinical perspective, there is no clinical algorithm robust enough to distinguish between these three arboviruses.…”

Untold stories of the Zika virus epidemic in Brazil

“…The development of point‐of‐care diagnostic tests that can be reliably used in areas with high incidence of other arboviruses is expected in the near future . Some mathematical models have suggested high seroprevalence in Northeast Brazil, but the data should be confirmed with other seroepidemiological surveys.…”