Two big health-care buyouts are shaping up to be among the worst-performing private-equity investments in recent years. The coronavirus pandemic is only the latest reason why. Physician-staffing firms Envision Healthcare Corp. and TeamHealth Holdings Inc., whose emergency-room workers are ubiquitous throughout the country, were purchased by KKR & Co. and Blackstone Group Inc. in 2018 and 2017 for roughly $6bn and $3bn, respectively.