What is the prevalence of West Nile virus infection in the US?

Updated: Apr 23, 2020
  • Author: Jess D Salinas, Jr, MD; Chief Editor: Elizabeth A Moberg-Wolff, MD  more...
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Answer

The West Nile virus was introduced into the United States in 1999, in New York City. Since then, the disease has occurred with greater frequency in the Southern, Midwestern, and Western states. Symptoms of the infection first appear in the population in early June, with the peak incidence occurring in late August and tapering through early November.

A large outbreak of West Nile virus infection in 2012 resulted in 5674 reported cases (51% of which were neuroinvasive), although the number of reported cases for 2013 dropped to 2469. In 2014, there were 2205 reported cases (61% of which were neuroinvasive), while in 2015, the number was 2175, with the incidence of neuroinvasive West Nile virus being 0.45 cases per 100,000 population nationally. [13, 14, 15, 16, 17, 18] In 2016, the number of US cases reported to the US Centers for Disease Control and Prevention (CDC) reached 2149, including 1309 neuroinvasive cases; the incidence of neuroinvasive disease was 0.41 per 100,000 population, comparable to the median incidence between 2002 and 2015. [19, 20] The infection data for 2018 was 2647 cases, including 1658 neuroinvasive disease cases. [21]  In total, 50,830 cases of West Nile virus were reported to the Centers for Disease Control and Prevention (CDC) between 1999 and 2018, including 24,657 cases of neuroinvasive disease. [21]

According to preliminary data from the CDC, there were 917 reported US cases of West Nile virus in humans in 2019, with the virus reported for that year in people, birds, or mosquitoes in 47 states and the District of Columbia. The disease was classified as neuroinvasive in 607 (66%) cases. [22]


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