The growing list of countries reporting cases of the illness include China, Hong Kong, Indonesia, Philippines, Singapore, Thailand and Vietnam. Most cases involve medical workers.

Doctors do not know what causes the illness -- or whether it is a virus or bacteria. [Julie Gerberding] said doctors are unsure whether antibiotics or antiviral drugs have an effect on the disease because they have not been consistently used in the areas with the most cases.

1 PIC; Patients at a Hong Kong hospital took precautions yesterday against the outbreak of a severe respiratory illness.