West Nile virus was the most common cause of domestically acquired arboviral disease in the United States in 2015, according to a report from the Centers for Disease Control and Prevention.

A total of 2,282 cases of arboviral disease were reported to the CDC in 2015. Of those, 2,175 cases were caused by the West Nile virus. Of the patients with WNV, 1,616 were hospitalized because of the disease, and 146 died. Neuroinvasive WNV, which occurred in 1,455 cases, accounted for 1,382 of 1,616 WNV hospitalizations and 142 of 146 deaths.

Neuroinvasive WNV cases were reported in 41 states and the District of Columbia, with California reporting both the highest number of cases at 585 and the highest infection rate at 1.49 cases per 100,000 people. Other states with a neuroinvasive WNV infection rate of more than 1 per 100,000 people included North Dakota, South Dakota, Nebraska, Colorado, and Oklahoma.

Of the 107 non-WNV arbovirus cases reported to the CDC, 55 were La Crosse virus, 23 were St. Louis encephalitis, 11 were Jamestown Canyon virus, 7 were Powassan virus, and 6 were eastern equine encephalitis. In addition to La Crosse and Jamestown Canyon, 4 cases of additional California serogroup viruses were reported, as was 1 case of Cache Valley virus.

“Health care providers should consider arboviral infections in the differential diagnosis of cases of aseptic meningitis and encephalitis, obtain appropriate specimens for laboratory testing, and promptly report cases to public health authorities. Because human vaccines against domestic arboviruses are not available, prevention depends on community and household efforts to reduce vector populations, personal protective measures to decrease exposure to mosquitoes and ticks, and screening of blood donors,” the CDC investigators concluded.

Find the full report in the MMWR (doi: 10.15585/mmwr.mm6602a3 ).