A lone patron masks at the Tatte Bakery & Cafe in Cambridge’s Kendall Square. (Photo: Marc Levy)

Cambridge Health Alliance reinstated masking requirements Monday in all “patient care areas” such as doctors’ offices, emergency rooms, laboratories and hospital wards because of rising numbers of Covid-19 infections in Massachusetts and locally. “We are seeing an increase in Covid-19 cases both in our patients and in our workforce,” CHA spokesperson David Cecere said Tuesday.

The change means that patients and other visitors to the affected areas must wear a mask once again. The Alliance will provide masks in the main lobbies of CHA Cambridge Hospital, CHA Everett Hospital and the CHA Somerville campus as well as primary care and other offices.

“Masking helps protect people as we move further into the fall and winter months,” Cecere said. A statement on the CHA website said: “We feel strongly that masking during viral respiratory season (flu, RSV, Covid) is an important step to protect our patients and employees from illness, especially those who are at highest risk.”

As Covid cases have ticked up – though they are still below the heights of the first Omicron outbreak last fall and winter – a few other hospitals have returned to masking requirements. In Massachusetts, Baystate Health, the Springfield-based health care system, now requires visitors and staff in patients’ rooms and care areas to wear masks. Staff with patient contact at UMass Memorial Hospital in Worcester must now mask. Nationally, about a dozen hospitals and health systems have reinstated masking, according to news reports.

More people are masking again as they enter public places such as stores and coffee shops, too.

New hospital admissions for Covid-19 in Middlesex County rose 5 percent in the first week of September compared with the previous week, according to the most recent report from the Centers for Disease Control and Prevention. The CDC classifies the county’s admission rate per 100,000 population as low.

Data from the state Department of Public Health shows the weekly average number of people hospitalized with Covid has been rising since the week of July 10. The most recent report of Covid patients in individual hospitals, as of Sept. 14, showed six Covid patients at the Cambridge Health Alliance, of whom two were in intensive care. Mount Auburn Hospital reported five Covid patients with none in intensive care. A spokesperson for Mount Auburn said the hospital hasn’t changed its masking policies “at this time” and continues “to monitor metrics related to respiratory viruses to determine when additional prevention measures may be needed, including a return to masking.”

Public health agencies can no longer rely on total reported case numbers because so many people are using home tests and are not reporting the results. Still, most experts agree infections are increasing. A more reliable measure – Covid levels in sewage – shows that concentrations in wastewater from the Massachusetts Water Resources Authority northern district, which includes Cambridge, have been on the rise since the beginning of July.