Top 5 Takeaways

  1. Decrease in West Nile Virus Incidence: The national incidence of neuroinvasive West Nile Virus (WNV) disease in 2020 was 59% lower than the median annual incidence from 2010-2019.
  2. Increase in Other Arboviral Diseases: Despite the decrease in WNV, the incidence for other domestic arboviral diseases was higher in 2020 compared to the median annual incidence of the previous 10 years.
  3. Implications for Healthcare: Healthcare providers are encouraged to consider arboviral infections in differential diagnoses during active mosquito and tick seasons, perform appropriate diagnostic tests, and report cases promptly.
  4. Impact of COVID-19 on Reporting: Changes in healthcare-seeking behaviors, COVID-19 diagnostic prioritization, and reporting challenges likely influenced the documented cases of arboviral diseases in 2020.
  5. Importance of Timely Surveillance: Accurate and timely surveillance is crucial for identifying outbreaks and guiding public health prevention efforts against arboviral diseases.

Original Article Author and Citation

Corresponding Author

Nicole P. Lindsey,

Suggested Citation

Soto RA, Hughes ML, Staples JE, Lindsey NP. West Nile Virus and Other Domestic Nationally Notifiable Arboviral Diseases — United States, 2020. MMWR Morb Mortal Wkly Rep 2022;71:628–632. DOI:


The 2020 surveillance data for nationally notifiable domestic arboviruses in the United States indicated significant changes in disease incidence compared to previous years, with a notable decrease in West Nile Virus cases but an increase in other arboviruses like La Crosse and St. Louis encephalitis viruses. These findings emphasize the ongoing impact of arboviruses on public health and the importance of sustained surveillance and preventive measures.


This report utilizes data from ArboNET, the national arboviral disease surveillance system, and includes only confirmed and probable cases. Incidence rates were calculated using 2020 U.S. Census Bureau midyear population estimates, focusing on neuroinvasive disease due to its severe nature and more consistent reporting.


The report discusses the implications of the 2020 data in the context of the COVID-19 pandemic, which likely affected both the reporting and incidence rates of arboviral diseases. It also notes the geographical and seasonal variations in arboviral disease cases, underlining the unpredictable nature of these diseases.


Despite the decrease in West Nile Virus cases in 2020, the threat from arboviruses remains significant, necessitating continued vigilance in surveillance, diagnostics, and public health messaging to mitigate the impact of these diseases.


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