Minnetonka-based UnitedHealth Group is part of a $2.2 billion deal to acquire a controlling interest in a physician-staffing company based in Washington state, according to a rating agency’s report issued Wednesday.

The deal was first announced in April, when the German dialysis company Fresenius Medical Care said it would sell to an investment consortium its holdings in Sound Inpatient Physician Holdings LLC.

On Wednesday, Moody’s Investors Service issued a report assigning a rating on debt related to the deal and identified the acquiring firms as Summit Partners and OptumHealth, the UnitedHealth Group division that is rapidly expanding its patient-care business.

The physician-staffing company is “primarily focused on providing hospital medicine,” Moody’s said in its report. “It also provides services across the acute episode of care including that for emergency rooms and critical care units. As of 2017, the company had 3,500 employees and roughly $1.3 billion in pro forma revenues.”

UnitedHealth Group did not immediately respond to a request for comment.

In its report, Moody’s said it based its rating in part on OptumHealth’s ownership stake. The agency also noted that “one of Sound’s customers owns a small take in the company, which Moody’s believes mitigates the risk of contract loss.”

During an investors conference last month, UnitedHealth Group CEO David Wichmann did not mention the physician-staffing company, but talked about growth prospects for patient care services.

About 32,000 employed or aligned physicians care for 15 million patients annually at OptumHealth, Wichmann said. Care-delivery services account for about two-thirds of OptumHealth’s projected revenue this year of about $24 billion.

“We expect OptumCare will be many multiples of its current size at full maturity,” Wichmann said, according to a transcript provided by the company.

In April, Fresenius said the deal is subject to regulatory approvals and anticipated to close in late 2018. Late last year, UnitedHealth announced a $4.9 billion deal to buy medical clinics run by Denver-based DaVita Inc., which is another large dialysis provider.

DaVita Medical Group served about 1.7 million patients per year at the time in nearly 300 clinics with primary and specialty care. It also operated 35 urgent-care centers and six outpatient surgery centers.