Mosquitoes are carriers (vectors) for many diseases, most commonly of West Nile Virus and Eastern Equine Encephalitis (EEE). Mosquitoes bite until the first heavy frost (usually end of October). Everyone participating in outdoor activities should take actions to protect themselves from mosquito bites.

What You Should Do

Protect yourself

  • Put screens on windows and doors. Fix screens that have holes.
  • At sunrise and sundown (when mosquitoes are most active), minimize outside activities. If you must be outside, wear long-sleeved shirts and long pants and use bug spray.
  • Use bug spray with DEET (N, N-diethyl-meta-toluamide). Make sure that bug spray does not have more than 30% DEET. Do not use bug spray with DEET on infants. more
  • Put mosquito netting over playpens and baby carriages.

Get rid of mosquito breeding grounds

  • Get rid of anything around your house and yard that collects water. One cup of water can produce thousands of mosquitoes!
  • Clean your gutters so that they can drain properly.
  • Remove any water from unused swimming pools or boats and cover them.
  • Change the water in birdbaths at least two times a week.
  • Help your neighbors, friends and family do the same things.

What We Do

Arboviral Surveillance

The risk of transmitting West Nile Virus (WNV) or Eastern Equine Encephalitis (EEE) to humans is linked to the presence of the mosquitoes which carry the diseases and the number of birds which contract them. Mosquitoes are therefore routinely collected and tested for the presence of these diseases from June through October in a cooperative effort with the Department of Environmental Management (DEM). DEM traps mosquitoes at various locations throughout Rhode Island and later separates the mosquitoes of each trap into 'pools' according to species. The State Health Laboratory tests each pool for the presence of virus. The Rhode Island State Biological Laboratory performs testing for West Nile Virus and EEE virus infection in human specimens year-round.

Mosquito Risk Assessment Matrix

Variable Low Risk Indicators Medium Risk Indicators High Risk Indicators
Physical Environment
Temperature @ dusk < 55° F 55° - 70° F > 70° F
Wind Velocity > 20 mph 10-20 mph < 10 mph
Relative Humidity Low Average High
Habitat Open, unshaded Partial Sun Woods, deep shade
Proximity > 2 miles 1-2 miles < 1 mile
Time of Day Mid-day [Other times] Dusk
Surveillance Data
Mosquito Density* < 20 / CDC Trap 20-50 / CDC Trap > 50 / CDC Trap
Mosquito Species None Bird-biting Cross-biting
Infected Mosquitoes None WNV; Highland J EEE
Infected Mammals, including humans None WNV EEE
Age of Mosquitoes Newly emerged adults Newly emerged - 2 wks > 2 wks***
- Month November - June July, October August, September


  • * A good indicator of “nuisance”
  • *** Rationale: Mosquitoes have had an opportunity for ~ 2 blood meals.


Rhode Island Department of Health in collaboration with the Department of Environmental Management and University of Rhode Island