Update: Outbreak of severe acute respiratory syndrome--worldwide, 2003.

CDC continues to support the World Health Organization (WHO) in the investigation of a multicountry outbreak of unexplained atypical pneumonia referred to as severe acute respiratory syndrome (SARS). This report includes summaries of the epidemiologic investigations and public health responses in several affected locations where CDC is collaborating with international and national health authorities. This report also describes an unusual cluster of cases associated with a hotel in Hong Kong and identifies the potential etiologic agent of SARS. Epidemiologic and laboratory investigations of SAPS are ongoing.