As Congress considers efforts to rein them in, private equity firms are buying up more physician practices, according to a new study. Private equity firms acquired 355 physician practices from 2013 to 2016, a number that jumped each year of the study, according to a research letter published Tuesday in JAMA. The number increased from 59 practices in 2013 to 136 practices in 2016. With approximately 18,000 group medical practices in the U.S., researchers said while private equity acquisitions increased across specialties during the study period, they still constituted a small proportion of practices. Those acquisitions continued in the years beyond those in the study period. The 355 practices bought up included 1,426 sites and 5,714 physicians. The majority of acquired practices (43.9%) were in the southern U.S., the study found. Practices acquired by private equity firms had several sites (a mean of four) and many physicians (a mean of 16.3 in each practice) with a mean of 6.2 physicians affiliated with each site.