During the early 2010s, Chikungunya and Zika virus (CHIKV and ZIKV) were introduced and spread throughout the Americas, leading to large outbreaks¹. Like Dengue virus (DENV) besides several other arboviruses, ZIKV and CHIKV are transmitted to humans by Aedes spp. mosquitoes, superimposing public health challenges toward historically dengue endemic regions. These arboviral infections are known to cause health complications to newborns of infected mothers, even in asymptomatic maternal infection involving preterm delivery, fetal anomalies, low birth weight, and miscarriage^{2, 3}.

While several seroprevalence rates have been reported for dengue in Brazil, serological surveys for chikungunya and zika infections are still scarce. This study aimed to evaluate the serological prevalence of CHIKV, ZIKV, and DENV among pregnant women in a public maternity hospital in the state of Rio de Janeiro, Brazil.

We conducted a cross-sectional study at the Hospital Municipal Mariana Bulhões, located in the municipality of Nova Iguaçu. The city is part of the Baixada Fluminense region, northwest of the state capital, and had approximately 800,000 inhabitants in 2017, with a low-to-middle socioeconomic index. While being the only public maternity hospital in Nova Iguaçu, it provides maternal-infant care to the neighboring municipalities and performs around 5,000 deliveries per year.

As eligibility criteria, we defined any pregnant women, above 18 years old, who were admitted to the emergency/pre-delivery room. We excluded women presenting severe/unstable clinical conditions at admission. Sample size calculation was based on the average of deliveries for the recruitment period, which occurred from July to December 2017, through a convenience sampling. A simple questionnaire was applied, containing limited demographic, obstetric, and clinical data. Self-reported previous history of dengue, zika, and chikungunya infections, as well as yellow fever vaccination, were probed. Acute arboviral suspect cases were defined on a clinical basis. Blood samples were collected at the same visit. Samples were assayed in duplicate with ELISA commercial kits for dengue, zika, and chikungunya, performed according to manufacturer instructions. “Borderline” results were considered as negative for this analysis. These included: Anti-DENV IgM (Serion Elisa Classic - Virion\Serion, Germany); Anti-DENV IgG (Euroimmun, Germany); DENV NS1 antigen (Panbio Dengue Early ELISA, South Korea); Anti-ZIKV IgM capture (Novagnost, Germany); Anti-ZIKV IgG (Euroimmun, Germany); Anti-CHIKV IgM and Anti-CHIKV IgG (Euroimmun, Germany).

This study was approved by the Instituto Oswaldo Cruz Ethics Committee (protocol number: 66996217.7.2002.5254). All participants signed an informed consent form.

A total of 349 pregnant women were enrolled, with no exclusions or refusals to participate. The average age was 26.9 years (Table 1). The average gestational age was 38.8 weeks. Participants came from different parts of the city, especially from the central and populous zones. Approximately 36% came from neighboring municipalities. Most pregnant women were admitted in labor (81%). No participants presented clinical manifestations of acute arboviral infections. When asked about the history of dengue, zika, and chikungunya, there were affirmative answers in, respectively, 6%, 12%, and 9% of the cases. Out of 168 participants who were asked about previous vaccination against yellow fever, only one answered affirmatively.

From the 349 specimens submitted to the different commercial ELISA tests, there were 163 IgG positive and 6 IgM positive specimens for ZIKV, corresponding to 47.2% (95% CI: 42.0 to 52.5) of seroreactivity. The positivity for DENV occurred in 310, corresponding to 88.8% (95% CI: 85.5 to 92.1). All specimens were negative for DENV NS1 antigen. As for CHIKV, 99 of the specimens had positive IgG, and none had positive IgM; thus, it corresponded to 28.4% (95% CI: 23.6 to 33.1) (Table 2).

Table 2

Results of ELISA tests for DENV ZIKV and CHIKV among 349 pregnant women in a public maternity hospital in Nova Iguaçu (RJ), from July to December 2017

Despite being a convenience sampling, serological surveys involving pregnant women recruited from health services are a good tool, since may offer a glimpse of the general population’s actual seroprevalence. Moreover, most of the Baixada Fluminense population is assisted by the public health system, like the participants in our study.

In comparison with two other chikungunya serological surveys carried out during 2017 in Brazil, our finding is superior to that of Netto et al.⁴ in Salvador (7.4%), and that of Cunha et al.⁵ in Riachão do Jacuípe (20%), both cities in the state of Bahia. Concerning zika, Netto et al.⁴ found even higher seroprevalence in Salvador (63.3%), highlighting a subgroup of 273 pregnant women with 69.3%, recruited between 2015-2016. In another study involving blood donors in São Paulo state, Slavov et al.⁶ demonstrated ZIKV seroreactivity obtained in 2015, 2016, and 2017 of 5.3%, 12.8% and 13.2%, respectively. Another study has found 61.3% of ZIKV IgG positive among mothers who gave birth between 2015 and 2016, during the peak of zika fever and microcephaly outbreak in Recife, Pernambuco state⁷. As for dengue, we have found a seroprevalence rate that approximates those most remarkable from population-based studies conducted in Brazil (4.0-91.1%).

Among the limitations of this study, there are the possible cross-reactions involving antibodies against DENV and ZIKV. This phenomenon typically occurs among flaviviruses and has long been known, leading to false positives in serological tests⁸. Neutralizing antibody tests, not used in this study, have been used in serological surveys, increasing specificity, and reducing this problem. The commercial test for ZIKV used herein is based on the non-structural protein NS1, generally considered more specific than certain targets of the envelop glycoprotein E⁹. Some studies reported satisfactory accuracy for this test^{10, 11}, while one did not¹².

Finally, these results reflect a scenario of dengue high endemicity in Baixada Fluminense, pointing out to the deficiency of vector control policies in recent decades. This context favored the emergence of Ae. aegypti-related new arboviruses, like chikungunya and zika, with high impact on public health. While showing significant seroprevalence, it also suggests the possibility of new and imminent epidemic waves, taking into account the observed proportion of susceptibility in our sample.

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