A day after officials announced plans for a new $600 million hospital and health-care network that would serve Prince George’s County and southern Maryland, the county’s top health official has been asked to step down.

Donald Shell, who said he was told Friday morning that it would be his last day, has served since 2007 as the county’s health director, one of the last holdovers from the administration of County Executive Jack B. Johnson (D). County Executive Rushern L. Baker III (D) had been widely expected to replace Shell, who sat in the audience and did not participate in Thursday’s news conference announcing a partnership with the University of Maryland Medical System.

Shell, a physician who specializes in “social medicine,” which is aimed at addressing biological, psychological and social needs, is a former medical officer for the 1996 Olympics, and has participated in numerous humanitarian efforts abroad.

He founded “Adam’s House” in Prince George’s, a center for treatment of substance abuse that aims to treat social as well as medical issues. The county’s health department has a $70 million annual budget. Deputy Director Elana Belon-Butler has been named acting director. Shell said he had not determined what his next post would be.