Dr. Alan Johnson said he volunteered in the Liberian capital of Liberia . He returned to the United States on August 25 . He was to be in Liberia for 21 days . Many American medical workers have been infected with Ebola in West Africa .
Dr. Alan Jamison says he volunteered in the Liberian capital of Monrovia . He returned to the United States on July 25 . He plans to be in isolation for 21 days . Two American medical workers have been infected with Ebola in West Africa .