Almost 3,000 cases of West Nile virus reported in U.S. in 2021

In 2021, there were 3,035 reports of arthropod-borne viruses (arboviruses) in the United States, including 2,911 caused by West Nile virus, according to research published in the August 25 issue of the U.S. Centers for Disease Control and Prevention Morbidity and Mortality Weekly Report.

Anna C. Fagre, D.V.M., Ph.D., from the CDC, and colleagues summarized 2021 surveillance data reported to the CDC by U.S. jurisdictions for nationally notifiable arboviruses.

The researchers identified 3,035 reported cases of domestic arboviral disease in 49 states and the District of Columbia, including 2,911 caused by West Nile, 40 by La Crosse, 32 by Jamestown Canyon, 24 by Powassan, 17 by St. Louis encephalitis, six by an unspecified California serogroup, and five by eastern equine encephalitis viruses. Sixty-nine percent of the West Nile disease cases were classified as neuroinvasive disease, for a national incidence of 0.61 cases per 100,000 population.

"Health care providers should consider arboviral infections in the differential diagnosis of aseptic meningitis and encephalitis, obtain appropriate specimens for laboratory testing, and promptly report cases to public health authorities, particularly during the summer months when most infections occur," the authors write.