Transmission of Chikungunya Virus in an Urban Slum, Brazil.

Rosângela O Anjos,Vánio André Mugabe,Federico Costa,Mitermayer G Reis,Guilherme S Ribeiro,Gielson A Sacramento,Caroline X Carvalho,Ricardo Khouri,Uriel D Kitron,Albert I Ko,Nivison R.R Nery,Patrícia S.S Moreira,Moyra M Portilho

doi:10.3201/eid2607.190846

Abstract

After a chikungunya outbreak in Salvador, Brazil, we performed a cross-sectional, community-based study of 1,776 inhabitants to determine chikungunya virus (CHIKV) seroprevalence, identify factors associated with exposure, and estimate the symptomatic infection rate. From November 2016 through February 2017, we collected sociodemographic and clinical data by interview and tested serum samples for CHIKV IgG. CHIKV seroprevalence was 11.8% (95% CI 9.8%–13.7%), and 15.3% of seropositive persons reported an episode of fever and arthralgia. Infections were independently and positively associated with residences served by unpaved streets, a presumptive clinical diagnosis of chikungunya, and recall of an episode of fever with arthralgia in 2015–2016. Our findings indicate that the chikungunya outbreak in Salvador may not have conferred sufficient herd immunity to preclude epidemics in the near future. The unusually low frequency of symptomatic disease points to a need for further longitudinal studies to better investigate these findings.

Highlights

After a chikungunya outbreak in Salvador, Brazil, we performed a cross-sectional, community-based study of 1,776 inhabitants to determine chikungunya virus (CHIKV) seroprevalence, identify factors associated with exposure, and estimate the symptomatic infection rate
In Brazil, CHIKV was first detected in September 2014, almost simultaneously in the cities of Oiapoque, in the northern state of Amapá, where the Asian genotype was implicated [7], and in Feira de Santana, in the northeast state of Bahia, where the East/Central/ South African (ECSA) genotype was detected [7,8]
In Salvador, the capital of Bahia state, which is located ≈100 km from Feira de Santana, we retrospectively identified that CHIKV had been circulating since September 2014 [15], but outbreaks first occurred between June and November 2015 [12,15]

Summary

Introduction

After a chikungunya outbreak in Salvador, Brazil, we performed a cross-sectional, community-based study of 1,776 inhabitants to determine chikungunya virus (CHIKV) seroprevalence, identify factors associated with exposure, and estimate the symptomatic infection rate. In certain Caribbean islands, such as Puerto Rico and the US Virgin Islands, the rate at which CHIKV infection was symptomatic was estimated at >70% [5,6] It remains unclear whether the attack rates in outbreaks in large population centers in the Americas created sufficiently high levels of herd immunity to preclude subsequent epidemics. In Salvador (population 2.9 million [14]), the capital of Bahia state, which is located ≈100 km from Feira de Santana, we retrospectively identified that CHIKV had been circulating since September 2014 [15], but outbreaks first occurred between June and November 2015 [12,15]. We investigated factors potentially associated with prior CHIKV infection

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