ON A NARROW road on the main campus of the Centres for Disease Control and Prevention (CDC) lies Building 21, the crescent-shaped headquarters of America’s premier public-health agency. In a room lined with television screens researchers monitor the measles outbreak that killed a second American in the southern plains last week and the bird-flu epidemic now ravaging flocks in every state. The agency’s leadership occupies the 12th floor. Military-grade security ensures that only authorised visitors and the CDC’s local workforce of roughly 5,000 civil servants have access.