Clinical and spatial features of Zika virus in Mexico

Background: Zika virus (ZIKV) is an emerging arbovirus transmitted to humans by Aedes mosquitoes, the same vectors that transmit dengue virus and chikungunya. Recent work has suggested that prior infection with dengue could lead to more severe clinical disease in ZIKV patients. Here, we describe the spatial distribution of and clinical symptoms experienced by ZIKV cases in Mexico. Methods: We performed Fisher's Exact test and Pearson's Chi-Square tests on data from Mexico's national surveillance system on the demographic and clinical characteristics of ZIKV patients (N = 84), and then a multivariate logistic regression analysis to determine demographic risk factors for patients presenting with at least 9 symptoms. We also mapped the cases to describe the spatial distribution of ZIKV in Mexico. Results: Results from the multivariate logistic regression analysis indicate that, controlling for all covariates, sex (male) is a significant protective factor in reporting a high number of symptoms (OR = 0.36, 95% CI: 0.14, 0.92), and that a one-year increase in age is associated with a 4% increase in odds of having at least 9 symptoms (95% CI: 1.00, 1.08). Spatial analysis revealed more than 50% cases reported within 50 k of railways. Conclusion: We found that sex and age are both significant risk factors for ZIKV infection severity, using number of reported symptoms as a proxy. The presence of cases along railways indicates that transportation networks within Mexico may be relevant for the national and international spread of the disease.