In the great illegal-immigration debate, one argument for lenience comes from law-enforcement officials who say undocumented immigrants are more likely to work with police if they’re not afraid of deportation.

Judging from recent events in the Boston area, there’s a similar case to be made involving public health.

As the Commonwealth's epidemiologist and the medical director of the Department of Public Health's Bureau of Infectious Disease, Dr. Alfred DeMaria works to track and contain the spread of illnesses across Massachusetts. Around the beginning of June, he learned about a cluster of mumps cases centered in East Boston, via reports relayed to DPH by local physicians.

"The beginning of mumps can be very nondescript, and very mild symptoms," DeMaria said. "The characteristic symptoms are swelling of the salivary glands."

But mumps can also be painful, DeMaria notes, and lead to more severe problems such as meningitis and encephalitis. At the time, the disease had already been popping up at local colleges and universities. But this cluster was different.

"Immigrants, primarily from South and Central America," DeMaria said, describing the effected population. "To see multiple cases potentially related to each other really made us concerned about ongoing transmission."

Adding to that concern: a prevailing mood of deep wariness among Boston-area Latinos.

"I have never seen a community in so much fear," says Gladys Vega, the executive director of the nonprofit Chelsea Collaborative.

In the Trump Era, Vega says, families that included one undocumented immigrant or more have taken to keeping a low profile, limiting their visibility and adhering to a strict regimen for mundane tasks like answering a knock at the door. In this environment, she adds, it's been hard to convince the people she works with to get even routine medical care.

"At our local clinic, people were not keeping their appointments," Vega said. "It got to a point that it was so bad that MGH professionals sent a letter to their patients, saying, 'Please come back to us, get your medical care, it’s important for you to come. This is a safe haven.'"

But when that mumps cluster became evident, public health officials needed that same community’s trust — to identify and isolate patients, track their recent interactions, and convince healthy people to get vaccinated.

In and around Boston, the response was led by the Boston Public Health Commission, where Rita Nieves is deputy director.

"We have relationships in the East Boston community, especially with the East Boston Neighborhood Health Center, so we contacted them," Nieves said. "Our outreach plan included doing targeted outreach — churches, for example, different educational programs. Schools, ESL [classes]."

The BPHC also tried to disseminate information via the Spanish-language media. (Vega, the head of the Chelsea Collaborative, did a local radio interview urging individuals to seek treatment as appropriate.) And it posted Spanish-language fliers that warned of possible exposure.

"Clubs is one of the places we did outreach to, and put signs saying, 'If you came to this club from this date to this date, you may have been exposed,'" Nieves said.

The good news? A few weeks later, that response seems to have worked.

"We haven’t seen any evidence of a spread," Nieves said.

Correlation isn't causation, of course, but local immigration policy may be one reason why. After all, Boston Mayor Marty Walsh has offered City Hall as a refuge from deportation, and Chelsea’s police chief has made working with undocumented immigrants a priority.

But if federal enforcement grows more aggressive, that sense of local trust could dissipate.

"The health-seeking behavior of people may change dramatically, if things continue to change in terms of immigration laws," said Nieves. "So we are concerned."

So now, as the Trump Administration weighs ramping up deportations, a message from epidemiologist Al DeMaria seems especially timely: his office doesn't share patients’ immigration status with federal authorities.

"We would never even ask the question, because it’s irrelevant to what we try to do," said DeMaria. "All we’re interested in is public health."