Massachusetts has the lowest rates of uninsured residents in the United States. But the average, 2.8%, masks some big differences.

Thirty communities in Massachusetts have no uninsured residents, while 137 communities have uninsured rates that range from 3.4% to 25.8%, according to a report released by the Blue Cross Blue Shield of Massachusetts Foundation.

(Courtesy of the Blue Cross Blue Shield of Massachusetts Foundation)

These so-called "hotspots" are often lower income, and have fewer residents with a high school diploma and high concentrations of young adults and non-citizens. Looking at the problem this way helps agencies and policymakers figure out where to target outreach and enrollment efforts, says Audrey Shelto, president of the foundation.

"We'll never get to 100% because some people will not be eligible [for insurance], but we should aim for as high as we can get," Shelto says.

The report, prepared by the Urban Institute, highlights pockets in and around Boston where there are between 61 and 1,603 uninsured residents per square mile. Sixty-five percent of the uninsured in Massachusetts are men. More than 40% are non-citizens who may be eligible for coverage if they are here legally.

Lili Silva, the vice president for operations and patient access at East Boston Neighborhood Health Center, says the findings will help her team figure out where — outside the health center — to look for people who might not understand their insurance options or need help applying for MassHealth.

But Silva says persuading people to sign up for Medicaid is becoming more difficult as the Trump administration ties immigration status to the use of public programs.

"We have patients calling and asking for reassurance about the process, and we've had a couple of people call to cancel their appointments," Silva says. "That concern and that confusion is out there."

The report identifies hotspots of uninsured children as well as adults, even though Shelto says "there should almost be no children who are uninsured because the benefits are available for most children."

(Courtesy of the Blue Cross Blue Shield of Massachusetts Foundation)

Some of the hotspots are communities with high housing costs: Somerville, Plymouth and Nantucket.

"For many uninsured residents in the high-priority communities, uninsurance is one of many challenges they face in meeting their basic needs," says report co-author Sharon Long.