Update: severe acute respiratory syndrome--worldwide and United States, 2003.

This report updates reported cases of severe acute respiratory syndrome (SARS) worldwide and in the United States, describes a change in the recommended timing of collection of a convalescent-phase serum specimen to test for antibody to SARS-associated coronavirus (SARS-CoV), and introduces a new case exclusion criterion based on negative SARS-CoV serology. In addition, this report also summarizes changes in travel alerts for Beijing and mainland China, Hong Kong, Toronto, and Taiwan.