MEDICINE: The Killers All Around

New viruses and drug-resistant bacteria are reversing human victories over infectious disease

They can strike anywhere, anytime. On a cruise ship, in the corner restaurant, in the grass just outside the back door. And anyone can be a carrier: the stranger coughing in the next seat on the bus, the college classmate from a far-off place, even the sweetheart who seems perfect in every way. For wherever we go and whatever we do, we are accosted by invaders from an unseen world. Protozoans, bacteria, viruses -- a whole menagerie of microscopic pests constantly assaults every part of our body, looking for a way inside. Many are harmless or easy to fight off. Others...