Spatiotemporal Dynamics and Environmental Drivers of Respiratory Syncytial Virus in Mexico

Abstract

Respiratory syncytial virus (RSV) is the most common cause of childhood acute lower respiratory tract infection. This virus accounts for 66,000-199,000 childhood deaths each year, 99% of which occur in developing countries. No vaccine is commercially available; treatment is currently limited to immunoprophylaxis with palizumab. In 2015, Pitzer et al. conducted an extensive study of RSV activity in the United States. This thesis aims to expand their analysis into Mexico. No study has explored nationwide RSV dynamics in Mexico. Bronchiolitis hospitalization data was used to explore the timing and amplitude of RSV activity in Mexico. Potential relationships between RSV activity and climatic, demographic, and geographic variables were considered using univariate and multivariate linear models. The minimal model was used to predict RSV activity. These analyses show that RSV activity in Mexico begins in the Yucatan peninsula in mid-October and spreads northwest through the country, peaking last in Sonora and Durango late in January. The southern states see more constant RSV activity and smaller relative outbreaks (outbreaks roughly 30% of the mean), while the north sees greater seasonal fluctuation and larger outbreaks (roughly 90% of the mean). The center of gravity and relative amplitude measures were highly correlated. Environmental factors were the strongest factors in univariate and multivariate regressions. Relative humidity, minimum temperature, specific humidity, and precipitation were significantly correlated with RSV activity (all p <0.01). Humid states with more precipitation and higher minimum temperatures saw RSV activity before drier, less humid states with more temperature fluctuation. Smaller outbreaks also occurred in these warm, humid, rainy states. A model containing phase values for specific humidity (timing of the most humid week) and mean annual and wet season specific humidity values was able to replicate RSV activity in the country. Equipped with an understanding of the spatiotemporal dynamics of RSV, health practitioners can tailor palizumab use to the months in which risk of RSV infection is highest. This reduces cost without risking the health of the patient.