The Centers for Disease Control and Prevention issued a warning ahead of the July 4 holiday weekend urging Americans to protect themselves against mosquito bites.

Federal health officials say West Nile virus cases are at a two-decade high to start 2026, with 48 cases reported through the end of June. The CDC said 38 of those cases involved severe neuroinvasive disease.

West Nile virus cases have been reported in 23 states so far this year.

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"These findings serve as an important reminder that mosquito season is well underway," CDC medical epidemiologist Dr. Erin Staples said. "As families gather outdoors to celebrate Independence Day, we encourage everyone to enjoy their holiday while taking simple steps to protect themselves and their loved ones from mosquito bites."

The CDC issued the following guidance for Americans this holiday weekend:

• Use an insect repellent registered with the Environmental Protection Agency.
• Wear long, loose-fitting shirts and pants to make it harder for mosquitoes to bite.
• Avoid being outside between dusk and dawn, when mosquitoes that spread West Nile virus are most active.
• Use window and door screens or air conditioning, if available, to keep mosquitoes outside.

The CDC said the virus commonly causes fever, headache, body aches, joint pain, vomiting, diarrhea or rash. Less than 1% of infected people develop severe neurologic disease, which can lead to long-term disability or death.

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Health officials said people 60 and older, as well as those with certain underlying medical conditions, are at increased risk for severe illness.