Epidemiologic and spatiotemporal trends of Zika Virus disease during the 2016 epidemic in Puerto Rico

Abstract

Background After Zika virus (ZIKV) emerged in the Americas, laboratory-based surveillance for arboviral diseases in Puerto Rico was adapted to include ZIKV disease. Methods and findings Suspected cases of arboviral disease reported to Puerto Rico Department of Health were tested for evidence of infection with Zika, dengue, and chikungunya viruses by RT-PCR and IgM ELISA. To describe spatiotemporal trends among confirmed ZIKV disease cases, we analyzed the relationship between municipality-level socio-demographic, climatic, and spatial factors, and both time to detection of the first ZIKV disease case and the midpoint of the outbreak. During November 2015-December 2016, a total of 71,618 suspected arboviral disease cases were reported, of which 39,717 (55.5%; 1.1 cases per 100 residents) tested positive for ZIKV infection. The epidemic peaked in August 2016, when 71.5% of arboviral disease cases reported weekly tested positive for ZIKV infection. Incidence of ZIKV disease was highest among 20-29-year-olds (1.6 cases per 100 residents), and most (62.3%) cases were female. The most frequently reported symptoms were rash (83.0%), headache (64.6%), and myalgia (63.3%). Few patients were hospitalized (1.2%), and 13 (<0.1%) died. Early detection of ZIKV disease cases was associated with increased population size (log hazard ratio [HR]:-0.22 [95% confidence interval-0.29,-0.14]), eastern longitude (log HR:-1.04 [-1.17,-0.91]), and proximity to a city (spline estimated degrees of freedom [edf] = 2.0). Earlier midpoints of the outbreak were associated with northern latitude (log HR:-0.30 [-0.32,-0.29]), eastern longitude (spline edf = 6.5), and higher mean monthly temperature PLOS NEGLECTED TROPICAL DISEASES

Estimating incidence of infection from diverse data sources: Zika virus in Puerto Rico, 2016

“…in 2016 (3). We expect if there had been more dengue and chikungunya cases, our framework would improve differentiation from ZIKV cases from other arboviral cases.…”

“…One of our key indicators, suspected arboviral cases, uses a broad case definition to capture all potential symptomatic cases, and likely includes cases caused by other circulating arboviruses, such as dengue and chikungunya viruses. However, these non-ZIKV cases presumably have had little impact on our indicator, as dengue and chikungunya were rare in Puerto Rico in 2016 (3). We expect if there had been more dengue and chikungunya cases, our framework would improve differentiation from ZIKV cases from other arboviral cases.…”

“…We collected data on suspected arboviral disease cases, suspected GBS cases, and infections detected among blood donors reported in Puerto Rico during January 1, 2016–December 31, 2016. A suspected arboviral disease cases was defined as any patient with clinically-suspected illness resulting from an arbovirus infection and reported through the Passive Arboviral Diseases Surveillance System (PADSS) in Puerto Rico (3,13). Suspected GBS cases were patients experiencing onset of neurological symptomatic characteristic of GBS (e.g., bilateral flaccid limb weakness (14)) reported through the GBS Passive Surveillance System–a surveillance system capturing GBS cases along with patients experiencing other neurological symptoms (e.g., encephalitis (14)) and operated by the Puerto Rico Department of Public Health (PRDH) with support from the Centers for Disease Control and Prevention (CDC) (15).…”

“…Given that laboratory testing identified very few dengue and chikungunya cases (3), we assumed most suspected arboviral cases were suspected Zika cases. We estimated the expected number of reported suspect arboviral cases as the product of population size ( N ), ZIKV infection prevalence ( z t ), and the probability of reporting a clinical suspect Zika case per infection ( p S | Z ) and fit the case data using the negative binomial distribution formulated as a mean and dispersion: For p S | Z , we used a beta-distributed prior to approximate a mean of 0.11 and 95% credible interval [CrI] of 0.01-0.24 based on Mier-y-Teran et al (21) ( p S | Z ∼ Beta(3.3, 27)) (Table 1).…”

“…The emergence and rapid spread of Zika virus (ZIKV), an arbovirus transmitted by Aedes species mosquitoes, in the Americas (1) resulted in large-scale epidemics throughout the tropical areas of the region. The first confirmed locally acquired ZIKV casein Puerto Rico was reported on December 31, 2015 (2), followed by more than 36,000 confirmed cases in 2016 (3). While confirmed cases provided an indicator of transmission intensity, reported cases represented a small proportion of actual infections (4) in part because many ZIKV infections are asymptomatic or mild, and are not captured by surveillance systems (5–7).…”