Cooler evenings do not make a September mosquito warning irrelevant. Chelsea was among the communities listed at high risk for West Nile virus in the Massachusetts update reported September 25, when the state’s confirmed human-case total reached 11.

The September 25 update brought the statewide total to 11 confirmed human cases. Two newly reported exposures were in Suffolk County and one in Middlesex County, according to Boston 25’s report of state information. County-level exposure reports do not identify a patient as a Chelsea resident.

Follow changing risk levels

Both the high-risk designation and the 11-case figure are from September 25. Risk maps and case totals can change. Residents can consult the Massachusetts arbovirus dashboard for subsequent updates when planning outdoor activities, alongside taking the mosquito precautions recommended by public-health officials.

Reduce the chance of a bite

The CDC’s prevention guidance emphasizes preventing mosquito bites. It recommends an EPA-registered insect repellent, long loose-fitting shirts and pants, and avoiding outdoor exposure from dusk to dawn when mosquitoes that spread West Nile are most active.

Door and window screens, or air conditioning when available, help keep mosquitoes outside. Follow a repellent’s directions and choose precautions appropriate to the activity rather than assuming a short walk or a cooler day cannot involve mosquitoes.

For children, follow the repellent’s label directions carefully. CDC advises against products containing oil of lemon eucalyptus or PMD for children under 3. Cover strollers and baby carriers with mosquito netting, and dress children in clothing that covers arms and legs.

Around the home, CDC’s mosquito-bite guidance recommends checking containers that hold water. Once a week, empty and scrub, turn over, cover or discard items such as buckets, toys, flowerpot saucers, birdbaths and trash containers. Repair holes in screens as well. These steps address places where mosquitoes can breed or enter a home.

CDC also describes household and community mosquito-control measures. Residents with questions about treatments or persistent mosquito problems should contact their local mosquito-control program or a qualified professional rather than improvise a pesticide application.

Symptoms to watch for

West Nile is spread through infected mosquito bites. CDC says no licensed human vaccine or medicine is available to prevent the disease, which is why reducing exposure remains central to its advice.

Most people infected with West Nile do not develop symptoms. Some develop fever, headache, body aches, vomiting, diarrhea or a rash. CDC’s symptom guidance says the risk of severe illness rises with age and with certain underlying conditions. Seek immediate medical attention for high fever, neck stiffness, muscle weakness, confusion or tremors, and tell the healthcare provider about possible mosquito exposure.