Cambridge residents are being urged to take extra precautions against mosquito bites after the city’s West Nile virus risk level was raised from moderate to high. Meanwhile, a cyanobacteria bloom continued to keep part of the Charles River closed to recreation.

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The two advisories are among several late-summer public health developments in Cambridge, alongside a statewide survey that local health officials hope will shed light on barriers residents face in accessing health care and other services.

West Nile risk raised to high

Cambridge’s West Nile virus risk level was raised to high Monday after Massachusetts health officials confirmed a second human case in Middlesex County. Neither person diagnosed is a Cambridge resident, Cambridge Public Health Department spokesperson Dawn Baxter said.

About 2,000 people in the United States are diagnosed with West Nile virus each year, according to the Centers for Disease Control and Prevention, though only about one in five develop symptoms. These can include fever, headache, body aches, vomiting, diarrhea or a rash. In less than 1 percent of cases do people develop a severe version of the illness affecting the central nervous system, which can cause meningitis, encephalitis or paralysis. The virus kills more than 130 people in the U.S.  each year.

The higher risk designation makes it more important that residents take precautions,  Baxter said, particularly older adults and people with weakened immune systems.

“Basically, the prevention methods remain the same,” Baxter said. “Avoiding mosquito bites is really the name of the game.”

Residents should use insect repellent, wear long sleeves and pants around dawn and dusk, make sure window and door screens are in good condition and remove even small amounts of standing water around their homes, Baxter said, noting that  “Kids’ toys, buckets in the backyard, or even something as small as a bottle cap sitting with water in it, that little amount of water can be a breeding ground for mosquitoes.”

West Nile virus at this point in the summer is not unusual, Baxter said. The virus typically first appears in mosquito samples before human cases emerge.

The threat generally persists until the first hard frost, typically in late October or early November, she said.

Cyanobacteria bloom closes part of Charles

Cambridge health officials are also monitoring a cyanobacteria bloom in the Charles River downstream of the Massachusetts Avenue Bridge.

The affected stretch remains closed to recreational water activities, and residents are being advised not to swim, fish or boat in the water or allow pets to swim in or drink from it.

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Baxter said the state is regularly testing the river and has not informed Cambridge officials of any change in the bloom’s extent. Last year, a bloom that began downstream gradually spread upriver over several weeks, eventually expanding upstream from the Massachusetts Avenue Bridge to the Cambridge Street Bridge/River Street Bridge.

If this year’s bloom similarly expands, the city will notify residents and post additional signs along affected portions of the river, Baxter said.

The advisory cannot be lifted until state testing produces two samples showing safe cyanobacteria levels taken one week apart, Baxter said. There is no clear timeline for when that will happen. Last year, it took a number of weeks.

Exposure to cyanobacteria can cause rashes, sore throats, headaches and muscle weakness in people who touch or swallow contaminated water, Baxter said. The danger is greater for pets, which can become severely ill or even die after exposure.

Samuel Lipson, the city’s environmental health director, said cyanobacteria blooms are fueled by warm, sunny conditions and elevated levels of nutrients such as phosphates, which can enter waterways through runoff from fertilized lawns. Unlike visible layers of blooms in smaller, still bodies of water, cyanobacteria in the Charles may appear only as a milky discoloration below the surface because the river is moving.

“It’s not like a pond where you have stillness allowing algae to form thick mats,” Lipson said. “Doesn’t mean it’s not toxic.”

Survey seeks a clearer picture of health inequities

At the same time officials warn residents about immediate environmental health risks, the Cambridge Public Health Department is encouraging them to participate in Massachusetts’ Community Health Equity Survey.

The anonymous statewide survey asks residents about their health and the barriers they face in accessing health care and other resources. Cambridge officials will receive city-specific data and be able to compare local results with those from elsewhere in Massachusetts.

“We know that there are health inequities out there,” Baxter said. “The more we know about what kind of barriers people are experiencing, the better positioned we are to do the outreach or provide the kinds of services and information that people need.”

Officials are particularly interested in hearing from groups whose experiences might be underrepresented in data, including older adults, immigrant communities, people of color and non-English speakers, for whom the survey is available in multiple languages, Baxter said.

“We really encourage people to take that survey, especially if they are in a group that may need some special attention or whose voices are not typically heard as loudly as they should be,” Baxter said.

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