Health Advisory

Summary

• The Fairfax County Health Department (FCHD) has identified the first West Nile virus (WNV) positive mosquito pools in the Fairfax Health District in 2024; the mosquitoes were collected on May 21 and May 23 in the Falls Church, McLean, and Springfield areas. One additional positive pool was reported for the following week in the Burke area.
• This timing is consistent with data collected since 2004, where the first WNV-positive pools are reported between early May and early July.
• Patients with a compatible clinical illness (meningitis, encephalitis, acute flaccid paralysis) should be tested for WNV, especially those at highest risk of serious WNV disease including adults 50 years old and above and those who are immunocompromised.

Suggested Actions

• Providers should consider WNV in their differential diagnosis for compatible clinical illnesses until the end of October, the end of mosquito season in Fairfax County.
• Patients should be informed of the risk of mosquitoes in transmitting diseases, the steps they can take to protect themselves from mosquitoes, and ways reduce the number of mosquitoes around their homes. Recommendations include:
  • Using a mosquito repellent that contains DEET, picaridin, IR3535, Oil of Lemon Eucalyptus (OLE), para-menthane-diol (PMD) or 2-undecanone.
  • Wearing long pants and long sleeves to cover exposed skin.
  • Avoiding areas where mosquitoes are especially common during peak biting times, particularly at dawn and dusk.
  • Taking steps to control mosquitoes around their yards by “tipping and tossing” items that hold water such as tires, buckets, flowerpots, corrugated downspout extensions, and other containers; and using larvicides, such as Mosquito Dunks, in water that cannot be eliminated.
  • Keeping doors, windows, and screens in good repair.
• If you have any questions regarding laboratory testing, please contact the Fairfax County Health Department Acute Communicable and Emerging Disease Program at 703-246-2433 or hdcd@fairfaxcounty.gov.
• Per the Virginia Regulations for Disease Reporting and Control, healthcare providers are required to report all confirmed cases of WNV to their local health department (FCHD disease reporting link: https://www.fairfaxcounty.gov/health/diseases-conditions/reporting).

Additional Information

• Over the last ten years (2014-2023), 29 cases of WNV have been reported to FCHD, an average of almost 3 cases reported every year. Of these cases, 69% had neuroinvasive disease and 4 died. The cases were geographically distributed throughout the entire Health District.
• Most persons with WNV infection are asymptomatic (70-80%) or have only mild illness with fever, headache and muscle aches that can last days to weeks. Such cases are rarely diagnosed or reported. Fewer than 1% develop neuroinvasive disease (meningitis, encephalitis, acute flaccid paralysis).
• WNV is primarily spread by infected Culex mosquitoes which obtain the virus from certain bird species. Summers with higher rain levels correlate to higher levels of mosquitoes.
• FCHD’s Division of Environmental Health routinely traps and tests mosquitoes for WNV throughout the Fairfax Health District every mosquito season.
• Fairfax Health District residents may request a mosquito inspection of their yard from FCHD’s Division of Environmental Health at 703-246-2201, TTY 711. This inspection will result in recommendations to decrease mosquito populations on residents’ property.
• Attached is the FCHD’s Vector-borne Disease Surveillance Report for May 2024. If you are interested in receiving this monthly report, please submit your request at https://redcap.link/health.advisories.