The United States has recorded 504 human West Nile virus cases across 41 states, including 363 of the more serious neuroinvasive form, according to CDC surveillance data current through Sept. 8. A national survey released two days later found that only about one in three adults knows the basic rule for using repellent alongside sunscreen, and fewer than one in five knows what to look for when choosing a repellent.
That combination is the story heading into the final weeks of mosquito season. The Annenberg Public Policy Center at the University of Pennsylvania found that 82 percent of adults correctly identified preventing bites and controlling mosquitoes in and around the home as the best defense against West Nile and dengue, and that 64 percent say they routinely take precautions. Execution is where households fall short, and the details that go wrong determine whether repellent works.
Severity explains why this matters more for some readers than others. Most people infected with West Nile virus never develop symptoms, but about seven in 10 cases reported to CDC this year involve neuroinvasive disease, which affects the central nervous system and can cause lasting injury or death. There is no human vaccine and no specific antiviral treatment.
The Four Details Most Households Get Wrong
Sunscreen goes on first. Only 31 percent of adults surveyed knew that CDC recommends applying sunscreen, letting it dry, then applying repellent. Nearly half, 49 percent, were unsure of the order.
Repellent should not go under clothing. Just 15 percent knew this, and 41 percent were unsure. Applying repellent to skin covered by fabric does not extend protection.
Look for EPA registration on the label. Only 18 percent identified this as the CDC recommendation. Nearly half were unsure, 30 percent wrongly chose a product containing more than 50 percent DEET, and 6 percent chose one described as natural. CDC guidance notes that concentrations above 50 percent DEET generally do not add protection.
Infants under 2 months should not get repellent at all. Just 53 percent of adults knew this, and 42 percent were unsure. The CDC prevention guidance recommends covering an infant carrier with mosquito netting instead.
The active ingredients CDC recommends looking for in EPA-registered products are DEET, picaridin, IR3535, oil of lemon eucalyptus, para-menthane-diol and 2-undecanone. The survey of 1,904 adults was fielded Aug. 4 to 17, with a sampling error margin of plus or minus 3.2 percentage points.
A Season That Turned Out Smaller Than Its Start Suggested
The national picture has shifted since midsummer. MedicalDaily reported in July on an unusually fast start to the season, with early counts running at their highest level in more than two decades.
The season did not sustain that pace. The count through Sept. 8 is significantly lower than the number reported at the same point in 2025, according to the Annenberg center's review of ArboNET figures.
Caveats belong with any West Nile number. ArboNET data are preliminary and subject to change, cases are counted by county of residence rather than where exposure occurred, and mild cases are substantially underreported, so counts of non-neuroinvasive disease should not be used to compare activity across places or years.
"Despite the drop in the number of West Nile Virus cases relative to 2025, taking precautions to prevent mosquito bites and control mosquitoes is important to uphold community public health," said Ken Winneg, the Annenberg center's managing director of survey research.
Adults Over 60 Carry the Real Severe-Disease Risk
Severe West Nile disease is concentrated, not universal. Adults over 60 and people with weakened immune systems face the highest risk of neuroinvasive illness, along with people managing certain chronic conditions, outdoor workers and residents of neighborhoods with standing water or poor drainage.
Public concern does not track that risk. Only 16 percent said they were worried that they or a family member would contract West Nile or dengue in the next three months, little changed over two years. Symptom recognition has slipped: 56 percent could not identify West Nile symptoms from a list, an increase of eight percentage points from last year.
Patrick E. Jamieson, who directs the Annenberg Health and Risk Communication Institute, placed responsibility on federal messaging. "The CDC needs to do a better job of informing the public about how to choose and apply insect repellent," he said.
Prevention Habits That Still Matter in September
Among adults who take precautions, 81 percent routinely remove standing water, but only 54 percent repair or replace window screens and 64 percent wear repellent, both lower than in 2024.
The steps that work are unglamorous. Use an EPA-registered repellent every time you go outdoors, especially at dusk and dawn, when the Culex mosquitoes that carry West Nile are most active. Empty anything that has held water for more than a few days, including flowerpot saucers, gutters, bird baths and buckets, since even a very small amount of standing water can breed mosquitoes. Wear loose long sleeves and pants outdoors in the evening, and keep screens intact.
Symptoms appear two to 14 days after a bite and may include fever, headache, body aches, nausea and fatigue. A sudden severe headache, stiff neck, confusion, muscle weakness or seizures after mosquito exposure is a medical emergency, because neuroinvasive disease can resemble a stroke. CDC updates its West Nile case data every one to two weeks from June through December, and transmission usually falls with the first sustained cold weather.
Key Questions Answered
Does sunscreen or insect repellent go on first? Sunscreen first. Let it dry, then apply repellent. Only 31 percent of surveyed adults knew this.
How many West Nile cases has the United States reported this year? CDC logged 504 cases across 41 states as of Sept. 8, including 363 neuroinvasive cases. The figures are preliminary and below the count reported at the same point in 2025.
What should a repellent label say? That the product is EPA registered. Recommended active ingredients include DEET, picaridin, IR3535, oil of lemon eucalyptus, para-menthane-diol and 2-undecanone. Concentrations above 50 percent DEET generally add no extra protection.
Is repellent safe for babies? Not for infants younger than 2 months. CDC recommends covering the carrier with mosquito netting instead.
Who faces the highest risk of severe illness? Adults over 60 and people with weakened immune systems, along with people managing certain chronic conditions and those with heavy outdoor exposure.
What symptoms require emergency care? A sudden severe headache, stiff neck, confusion, muscle weakness or seizures after possible mosquito exposure. Neuroinvasive West Nile can resemble a stroke and needs immediate care.
