Health Alert: The outbreak of Severe Acute Respiratory Syndrome (SARS) in Asia continues to intensify, causing the U.S. Centers for Disease Control (CDC) to advise those planning nonessential travel to mainland China, Hong Kong, Singapore and Hanoi, Vietnam that they “may wish to postpone their trips until further notice.” The World Health Organization (WHO) issued a similar advisory April 2 encouraging travelers to consider postponing all but essential travel to Hong Kong and Guangdong Province. WHO issued the advisory because about 20 cases in Hong Kong did not fit the typical pattern of transmission. The disease has been predominantly spread to health care workers or others who have come into close contact with infected persons, but in these Hong Kong cases the individuals did not appear to have been in such close contact. Travelers returning from places where the outbreak has occurred should be aware of the disease’s symptoms, which include a temperature of greater than 100.4 degrees Fahrenheit, and evidence of respiratory illness including cough, shortness of breath, difficulty in breathing, hypoxia (deficiency in the amount of oxygen reaching the tissues of the body), and X-rays indicating the presence of pneumonia. Cases have occurred in 15 countries around the world because travelers have flown internationally not knowing they were infected, but the highest concentrations have been in Guangdong Province of China, Hong Kong, Singapore, and Hanoi, Vietnam. The government of Ontario, Canada declared a health emergency in the province because of three deaths and the infection of more than 50 others. Two major hospitals have been closed or restricted as a precaution. For updates on this developing situation, visit the CDC and WHO web sites (www.cdc.gov and www.who.int).