Health Advisory

Summary

• The Fairfax County Health Department (FCHD) has identified its first West Nile virus (WNV) positive mosquito pool in the Fairfax Health District in 2023; the mosquitoes were collected on June 27 (week 26) in the Falls Church area. No additional positive pools were reported for that week or the following week (week 27).
• FCHD identifies WNV in mosquitoes throughout the Health District every year. Since 2009, the first WNV-positive pool has been reported between mid-May (week 21) and mid-July (week 29).
• WNV should remain in healthcare providers’ differential diagnosis until the end of the mosquito season in Fairfax County (end of October~ week 44).

Suggested Actions

• 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 (adults 50-years-old or older and those whose immunity is suppressed due to disease or medication).
• 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).
• 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.

Additional Information

• Over the last ten years (2013-2022), 29 cases of WNV have been reported to FCHD, an average of almost 3 cases reported every year. Of these cases, 72% had neuroinvasive disease and 4 died. The cases were geographically distributed throughout the entire Health District. 83% developed symptoms in August or September.
• 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 Disease Carrying Insects Program routinely traps and tests mosquitoes for WNV throughout Fairfax County every mosquito season.
• Fairfax County residents may request a mosquito inspection of their yard from the Health Department’s Disease Carrying Insects Program at 703-246-8931, TTY 711. This inspection will result in recommendations to decrease mosquito populations on residents’ property.