Results
Reported Arboviral Disease Cases
CDC received 1,955 reports of confirmed (594; 30%) and probable (1,361; 70%) arboviral disease cases with illness onset in 2024; 1,485 cases (76%) were neuroinvasive (Table 1). Cases were reported from 647 (21%) of 3,143 U.S. counties and from 48 states and the District of Columbia (DC). WNV accounted for 1,808 (92%) cases, followed by Powassan (60; 3%), La Crosse (37; 2%), Jamestown Canyon (27; 1%), eastern equine encephalitis (19; 1%), St. Louis encephalitis (2; <1%), and unspecified California serogroup viruses† (2; <1%). The specific virus was unknown for two cases with California serogroup virus; these cases were excluded from further description in this report.
WNV Disease
In 2024, a total of 1,808 WNV disease cases were reported; median patient age was 64 years (interquartile interval [IQI] = 51–73 years), and 1,133 (63%) patients were male (Table 1). Three fourths (1,347; 75%) of patients had WNV neuroinvasive disease. A total of 1,396 (77%) patients were hospitalized, including 1,263 (91%) with neuroinvasive disease. Overall, 173 (9.6%) patients with reported WNV disease died, 169 (98%) of whom had neuroinvasive disease (case-fatality rate [CFR] = 13% among patients with neuroinvasive disease). A majority of patients had illness onset during July–September (1,523; 84%). Two neuroinvasive WNV disease deaths were reported in patients who were infected through kidney transplantation from a single deceased organ donor.
WNV disease cases were reported from 591 (19%) of 3,143 counties in 48 states and DC. Texas (363 cases), California (103), and New York (69) accounted for 40% of all U.S. WNV neuroinvasive disease cases. The national incidence of WNV neuroinvasive disease was 0.40 per 100,000 population (Table 2), and incidence was highest in North Dakota (2.76), Nebraska (2.49), and Mississippi (1.43) (Figure). Incidence was higher among males (0.52) than females (0.28) and among adults aged ≥70 years (1.30) than persons in other age groups. Incidence was lowest among children aged <10 years (0.02).
The 1,808 reported WNV disease case count in 2024 is below the 10-year median of 2,162 cases (IQI = 1,132–2,628). The 456 cases reported in Texas are more than double the number reported in Texas in 2023 (163).
Powassan Virus Disease
In 2024, a total of 60 Powassan virus disease cases were reported. The median patient age was 69 years (IQI = 60–75 years), with four patients (7%) aged <18 years, and 35 (58%) patients were male (Table 1). All patients were hospitalized with neuroinvasive disease, and nine died (CFR = 15%). Cases occurred throughout the year, and approximately one half (28; 47%) had illness onset during April–June.
Powassan virus disease cases were reported from 45 counties across 10 states. Nationally, the incidence of neuroinvasive Powassan virus disease was 0.02 per 100,000 population, with the highest incidence in Maine (0.43), Minnesota (0.24), New Hampshire (0.21), and Wisconsin (0.20) (Table 2). From 2023 to 2024, Minnesota and Wisconsin experienced a combined 160% relative increase in cases, from 10 to 26. Nationally, the number of cases reported in 2024 was above the 10-year median of 23 cases (IQI = 21–43), and during the previous 21 years, cases increased with an annual growth rate of 17.5% (95% CI = 13.6–21.6; negative binomial regression; p<0.001).
La Crosse Virus Disease
In 2024, a total of 37 La Crosse virus disease cases were reported; 35 (95%) occurred among children aged <18 years (median age = 8 years; IQI = 5–10 years), and 19 (51%) occurred among females. Overall, 36 (97%) patients were hospitalized, 36 (97%) had neuroinvasive disease, and none died (Table 1). Illness onset occurred during July–September among 32 (86%) patients. Cases were reported from 24 counties in eight states. Overall, 75% of neuroinvasive La Crosse virus disease cases were reported from North Carolina (15) and Tennessee (12), representing a relative increase of 170% from five cases in each state reported in 2023, although the number of cases in 2024 was below the 10-year median (55 cases; IQI = 35–80). The national incidence of neuroinvasive La Crosse virus disease was 0.01 per 100,000 population (0.05 among children aged <18 years) and was highest in Tennessee (0.17), North Carolina (0.14), and West Virginia (0.06) (Table 2).
Jamestown Canyon Virus Disease
In 2024, a total of 27 cases of Jamestown Canyon virus disease was reported; the median patient age was 66 years (IQI = 53–76 years), and 19 (70%) patients were male. Twenty-one (78%) patients were hospitalized, 20 (74%) had neuroinvasive disease, and two (7%) died (CFR = 10% among patients with neuroinvasive disease) (Table 1). Illness onset occurred during July–September for 13 (48%) patients and April–June for 10 (37%). Cases were reported from 23 counties in six states. The highest numbers of cases were reported from Wisconsin (10), Michigan (eight), and Minnesota (four). The national incidence of neuroinvasive Jamestown Canyon virus disease was 0.01 per 100,000 population, with the highest incidences in New Hampshire (0.14), Wisconsin (0.10), Rhode Island (0.09), and Michigan (0.08) (Table 2). The number of Jamestown Canyon virus disease cases in 2024 was similar to the 10-year median (21 cases; IQI = 12–41).
Eastern Equine Encephalitis Virus Disease
In 2024, a total of 19 cases of eastern equine encephalitis virus disease were reported; the median patient age was 68 years (IQI = 53–78 years), and 15 (79%) patients were male. All patients were hospitalized with neuroinvasive disease, and five died (CFR = 26%) (Table 1). Eighteen (95%) patients had illness onset during July–September. Cases were reported from 12 counties in nine states. The highest numbers of cases were reported by New Hampshire (five) and Massachusetts (four). The national incidence of neuroinvasive eastern equine encephalitis virus disease was 0.01 per 100,000, and rates were highest in New Hampshire (0.35) and Vermont (0.31) (Table 2). The number of reported eastern equine encephalitis disease cases in 2024 was the highest since 2019 and higher than the 10-year median of 6.5 (IQI = 5–8).
St. Louis Encephalitis Virus Disease
Two cases of St. Louis encephalitis virus disease were reported in 2024, both in men aged <60 years. One patient was hospitalized with neuroinvasive disease, and both survived (Table 1). Illness onsets occurred in August and November. One neuroinvasive case was reported from Texas corresponding to an incidence of <0.01 per 100,000 population (Table 2). The number of St. Louis encephalitis virus disease cases was the lowest since 2013 and substantially lower than the 10-year median of 16.5 cases (IQI = 10–21).
