# Epidemiology of West Nile Virus in New York City: Trends and Transmission Dynamics (2000–2019)

## TL;DR

This study tracks West Nile Virus in New York City from 2000 to 2019, showing how mosquito species like Culex salinarius are linked to human infections and how climate change may be increasing outbreaks.

## Contribution

The study identifies Culex salinarius as a key vector in human WNV transmission and highlights climate-driven trends in urban WNV activity.

## Key findings

- Cx. salinarius, though a small proportion of positive mosquito pools, is strongly correlated with human WNV cases.
- 69% of human WNV cases occurred near WNV-positive mosquito pools, indicating localized transmission hotspots.
- Climate change likely contributes to increased WNV activity in NYC through warmer summers and extended mosquito breeding seasons.

## Abstract

The 1999 outbreak of West Nile virus (WNV) in New York City (NYC) marked the first documented introduction of the virus into the western hemisphere, prompting extensive public health surveillance. This study examines the epidemiology of WNV from 2000 to 2019, analyzing 381 human cases, including 66 cases of West Nile Fever (WNF) and 315 cases of West Nile Neuroinvasive Disease (WNND), with 35 fatalities. Simultaneously, 6632 WNV-positive mosquito pools were identified across 16 species. While Culex pipiens and Cx. restuans accounted for 91.4% of positive pools, Cx. salinarius, which comprised only 6.2%, exhibited a stronger correlation with human infections. Human surveillance involved comprehensive case investigations following laboratory-confirmed WNV infections, incorporating structured interviews with patients and healthcare providers. Mosquito surveillance was conducted through weekly collections from 52–71 permanent trap sites, supplemented by approximately 200 additional sites annually in areas with elevated WNV activity. Captured mosquitoes were species-identified, pooled, and tested for WNV RNA via RT-PCR. Findings highlight the dominant role of Culex species, particularly Cx. salinarius, in human WNV transmission, with 69% of cases occurring near WNV-positive mosquito pools. Spatial analyses identified transmission hotspots, emphasizing the importance of species-specific mosquito control strategies. Over the study period, WNV activity has increased in NYC, likely influenced by climate change, as warmer summers and extended breeding seasons align with peak outbreaks. Integrating spatial mapping, climate forecasting, and targeted surveillance could significantly improve WNV mitigation efforts in urban environments.