Ms. Baker’s employer, New Health Community Health Center, has laid off more than a third of its work force — 60 out of 175 — over the last two weeks, as revenues plummeted from fewer paid patient visits. “It’s heartbreaking for us,” said Desiree Sweeney, the executive director of New Health. “They’re good people.”

The nation’s latticework of nonprofit community health centers was first established in the 1960s and now stretches across every state to provide about 29 million people with primary care, regardless of their ability to pay. Almost a quarter of the centers’ patients are uninsured, and almost 70 percent live in poverty. The centers are a crucial link in a fragmented American health care system that too often fails to reach into poor neighborhoods.

Recent years have been pretty good for these places. When most states expanded Medicaid under the Affordable Care Act to cover many previously uninsured low-income adults, many community health centers saw their revenues improve, sometimes dramatically. But now, the centers are being battered by ferocious crosswinds as routine medical care — including dental work, a primary source of revenue — has been put on hold to conserve resources and keep the coronavirus from spreading.

At the same time, doctors and administrators in clinics from Massachusetts, Kentucky, Idaho, Iowa and Washington State said they are being put in a new role: working with hospitals to screen people for the virus, while bracing for a surge in patients if those hospitals become overwhelmed and people have nowhere else to go. Plus preparing for a time of greater economic pain in their already struggling patient populations.