Seroprevalence of Chikungunya Virus in a Rural Community in Brazil

<div><p>Background</p><p>The emergence of the Chikungunya virus (CHIKV) is currently expanding. In 2015, 38,332 cases of Chikungunya were reported to the Brazilian epidemiological surveillance system. Eighteen months after notification of the first case in the city of Feira de Santana, we conducted the first serosurvey to define the magnitude of transmission in a rural community in Brazil.</p><p>Methodology/Main findings</p><p>The serosurvey was conducted in a random sample of 450 residences in the Chapada district, located 100 kilometers from Feira de Santana. We administered questionnaires and tested 120 sera from Chapada district residents for CHIKV IgM- and IgG-specific antibodies. An individual with CHIKV infection was defined as any person with CHIKV IgM or IgG antibodies detected in the serum. One Hundred cases of Chikungunya were reported after prolonged rainfall, which reinforced the relationship between the rainfall index and CHIKV transmission. Eighteen months after the start of the outbreak, we identified a seroprevalence of 20% (95% CI, 15.4–35%). CHIKV IgG- and IgM-specific antibodies were detected in 22/120 (18.3%) and 6/120 (5.0%) individuals, respectively. Among seropositive patients, 13/24 (54.2%) reported fever and joint pain over the previous two years (p<0.01). The rate of symptomatic CHIKV infection was 40.7%.</p><p>Conclusions/Significance</p><p>We identified a moderate seroprevalence of Chikungunya in the Chapada district, and in half of the confirmed CHIKV infections, patients reported arthralgia and fever over the previous two years.</p></div

Numbers of CHIKV cases, anti-CHIKV IgM status and monthly precipitation in the Chapada district between October 2014 and November 2015.

<p>Numbers of CHIKV cases, anti-CHIKV IgM status and monthly precipitation in the Chapada district between October 2014 and November 2015.</p

Flow chart of the study enrollment and CHIKV IgM and IgG antibody positivity rates.

<p>Flow chart of the study enrollment and CHIKV IgM and IgG antibody positivity rates.</p

Description of 120 individuals enrolled in the serosurvey in the Chapada district.

<p>Description of 120 individuals enrolled in the serosurvey in the Chapada district.</p

Seroprevalence of IgM and IgG antibodies against CHIKV in Chapada, April 2016 (N = 120).

<p>Seroprevalence of IgM and IgG antibodies against CHIKV in Chapada, April 2016 (N = 120).</p

Comparison of individuals with CHIKV IgG- and/or IgM-positive and negative antibodies in the Chapada district (N = 120).

<p>Comparison of individuals with CHIKV IgG- and/or IgM-positive and negative antibodies in the Chapada district (N = 120).</p