New York City health officials say this year’s West Nile virus outbreak has already eclipsed last year’s entire total.
At least 30 residents have been diagnosed with the mosquito-borne illness since the first case was announced in early August, according to city health data. That figure tops the 18 cases recorded across all of 2025.
Brooklyn has been hit hardest, with 11 confirmed infections. Queens and Staten Island each report seven cases, the Bronx has three, and Manhattan has two.
The severity of this year’s outbreak is especially striking. Of the 30 confirmed cases, 24 are classified as West Nile neuroinvasive disease — the dangerous form that can cause encephalitis, meningitis, or acute flaccid paralysis. Just six cases are the milder West Nile fever, with no central nervous system involvement.
Sally Slavinski, who directs the city health department’s Zoonotic and Vector-Borne Disease unit, told Gothamist that warmer temperatures are driving the surge.
“We know that warmer temperatures can accelerate the mosquito life cycle and speed up viral replication in the mosquito, so that’s gonna shorten the time that it takes for there to be an infected mosquito and then transmit that virus,” Slavinski said.
“With this increased rainfall and humidity, it makes it easier for mosquitoes to thrive,” she continued. “These longer, warmer seasons where we’re having mosquitoes appear earlier and are active later in the year, there’s more opportunity for transmission to occur.”
The mosquito population itself tells the same story. City data shows over 1,700 positive mosquito pools detected this year, compared to roughly 1,300 in 2025 — a record high, according to Slavinski.
The health department monitors mosquito populations and applies pesticides during summer months to curb their numbers.
West Nile virus remains the only mosquito-borne disease known to spread to humans in New York City, where it has circulated for more than 25 years.
Most infected people never show symptoms. About one in five develop mild illness with fever, headache, body aches, nausea, or vomiting.
Slavinski noted that the high proportion of severe neuroinvasive cases likely reflects who actually gets tested, not the true spread of infection.
“Young, healthy people are not even realizing they may be infected or might have some mild illness,” she told Gothamist. “These are folks that are not necessarily getting tested.”
“So we don’t know about these folks that weren’t sick or had mild illness,” she added.
The people who do end up in testing data, Slavinski explained, are typically those facing serious illness.
“The people that are more likely to get tested are the people who are really sick; they’re getting hospitalized, and they’re getting worked up,” she said. “These are the folks with West Nile neuroinvasive disease.”