Private equity firm Thomas H. Lee has acquired medial personnel firm Healthcare Staffing Services from Altaris Capital Partners. Financial terms were not disclosed.

Healthcare Staffing, founded in 1989 and with headquarters in Denver, provides nursing staffing services on an urgent basis and usually for extensive periods of time.

“With this investment we will have the scale and resources to accelerate our growth and further expand our platform,” says Healthcare Staffing chairman Ray Marcy.

In 2014, Healthcare Staffing bought two other medical professional firms in Fastaff Travel Nursing and U.S. Nursing Corporation. In another similar deal announced earlier in 2015, Aequor Healthcare Services has acquired Therapy Staff LLC. The target focuses recruiting and hiring therapists.

Harris Williams & Co. advised Healthcare Staffing.