Danger from the Middle East. Centers for Disease Control and Prevention (CDC) guidance regarding the Middle East respiratory syndrome (MERS) has been updated. Clinicians should now test patients "who meet certain clinical and epidemiologic criteria" for the associated coronavirus (MERS-CoV). The CDC states that, "testing for MERS-CoV and other respiratory pathogens can be done simultaneously and that positive results for another respiratory pathogen should not necessarily preclude testing for MERS-CoV." The CDC also recommends investigating clusters of severe acute respiratory illness even when there's been no obvious exposure to MERS-CoV. Three more cases were confirmed in Saudi Arabia on August 1; two, though mild, were in exposed health care workers. No cases have yet been reported in the United States, but the CDC warns health care systems to be prepared for rapid action. Information on specimen collection and testing, case definitions, and infection control is available at http://1.usa.gov/11a5hDj. Interim guidance for clinicians can be found at http://1.usa.gov/17PRTqt.