As Americans worry about Ebola, the swiftly spreading virus that has traveled from West Africa to Texas, a more silent killer poses a greater danger. It sounds pedestrian, easy to dismiss. That’s what makes it so devastating. The U.S. health system is now under assault by antibiotic-resistant superbugs. Drug-resistant bacteria killed 23,000 people in America last year and caused 2 million illnesses. It is getting worse, health experts say. Fears of Ebola have ratcheted up since the Centers for Disease Control and Prevention announced last week that the first case of the disease had been diagnosed on U.S. soil. But unlike Ebola, which officials insist has little chance of getting out of control domestically, some bacterial infections are now resistant to all antibiotics and are completely untreatable. Doctors and others in American medicine have unparalleled knowledge about the spread of illness, but they can do little to fend off superbugs unless there is a big decline in the use of antibiotics and a rapid increase in the development of new drugs to treat seemingly routine ailments.