Press Releases


Last Mosquito Advisory of the Season: Although No New Findings of Arbovirus, State Urges Residents to Prevent Bites until First Hard Frost

PROVIDENCE The Department of Environmental Management (DEM) today announced that the final round of mosquito testing for 2021 conducted by the Rhode Island Department of Health (RIDOH) State Health Laboratories has confirmed no new positive findings of either West Nile Virus (WNV) or Eastern Equine Encephalitis (EEE). DEM collected 158 samples of mosquitoes from 45 traps set statewide Sept. 29 to Oct. 12. Trapping has concluded for the 2021 mosquito season.

For the season, the RIDOH State Health Laboratories tested 2,598 mosquito pools collected from June 2 through Oct. 12, six of which tested positive for WNV (two positive pools in East Providence and a single pool each in Cranston, Warren, Johnston, and Glocester). No mosquito pools tested positive for EEE.

However, Rhode Island has experienced one human case of WNV, which RIDOH announced Oct. 7. Also, to date this mosquito season, 208 pools of mosquitoes trapped in Connecticut and 144 mosquito pools in Massachusetts have tested positive for WNV. Connecticut confirmed two WNV cases in humans and Massachusetts confirmed nine human cases and one case in an alpaca. Connecticut confirmed two positive EEE findings in mosquito samples. Although mosquito populations are naturally reduced at this time of year, the likelihood of an individual mosquito carrying a disease is higher and DEM and RIDOH are reminding Rhode Islanders to avoid being bitten until the first hard frost. (A hard frost is when the air and the ground freeze below 32F for three hours or below 28F for two hours.) The two state agencies also remind constituents that because the weather is cooler, mosquitoes that remain in the environment may be more apt to fly into households when doors are opened.

Personal protection is the first line of defense against mosquitoes that may carry WNV, EEE, or other diseases and the most effective way to avoid infection. With WNV established in the state, residents are reminded to eliminate mosquito breeding grounds and prevent being bitten, whenever possible. The following precautions are advised.

Protect yourself:

- Put screens on windows and doors. Fix screens that are loose or have holes.

- At sunrise and sundown (when mosquitoes that carry EEE are most active), consider rescheduling outdoor activities that occur during evening or early morning. If you must be outside, wear long-sleeved shirts and long pants and use bug spray.

- Use EPA-approved bug spray with one of the following active ingredients: DEET (20-30% strength); picaridin, IR3535; and oil of lemon eucalyptus or paramenthane. Always read the label and follow all directions and precautions.

- Do not use bug spray with DEET on infants under two months of age. Children should be careful not to rub their eyes after bug spray has been applied on their skin. Wash children's hands with soap and water to remove any bug spray when they return indoors.

- 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. Just one cup of water can produce hundreds of mosquitoes; an unused tire containing water can produce thousands of mosquitoes.

- Clean your gutters and downspouts so that they can drain properly.

- Remove any water from unused swimming pools, wading pools, boats, planters, trash and recycling bins, tires, and anything else that collects water, and cover them.

- Remove or treat any shallow water that can accumulate on top of a pool cover. Larvicide treatments, such as Mosquito Dunks can be applied to kill immature mosquitoes. This environmentally-friendly product is available at many hardware and garden stores and on-line.

- Change the water in birdbaths at least once a week and rinse out birdbaths once a week.

Best practices for horse owners:

Horses are particularly susceptible to WNV and EEE. Horse owners are advised to vaccinate their animals early in the season and practice the following:

- Remove or cover areas where standing water can collect.

- Avoid putting animals outside at dawn, dusk, or during the night when mosquitoes are most active.

- Insect-proof facilities where possible and use approved repellents frequently.

- Monitor animals for symptoms of fever and/or neurological signs (such as stumbling, moodiness, loss of appetite) and report all suspicious cases to a veterinarian immediately. If you are unsure if your horse is properly vaccinated, you should consult with your veterinarian.

Visit for additional mosquito prevention tips, videos, and local data. DEM and RIDOH also remind Rhode Islanders to take precautions to avoid mosquito bites when traveling to Zika-affected countries. Pregnant women and women who are considering becoming pregnant should not travel to countries with active transmission of Zika. Mosquitoes are trapped weekly by DEM and tested at the RIDOH State Health Laboratories. DEM issues advisories on test results from July through mid-October, with additional reports as necessary. Typically, positive test results trigger additional trapping to assess risk.

For more information about DEM divisions and programs, visit or follow us on Facebook, Twitter (@RhodeIslandDEM), or Instagram (@rhodeisland.dem).

Related links

  • Department or agency: Department of Environmental Management
  • Online:
  • Release date: 10-28-2021

Share this: