Update: severe acute respiratory syndrome--United States, May 21, 2003.

CDC continues to work with state and local health departments, the World Health Organization (WHO), and other partners to investigate cases of severe acute respiratory syndrome (SARS). This report updates SARS cases reported worldwide and in the United States and highlights recent modifications to the U.S. SARS case definition that define criteria for exclusion of previously reported SARS cases and for reporting travel-associated cases of SARS.