In March, the head of the Centers for Disease Control issued an alarm, echoed by virtually every health authority in the world, that antibiotic-resistant bacteria threaten to return humans to the days when ordinary infections routinely killed and maimed. Yet the United States continues to use at least 70 percent of its antibiotics on livestock. Millions of pounds of antibiotics are routinely administered at low doses to large numbers of animals living in crowded conditions ... to speed their growth and prevent possible infections, creating ideal conditions for bacteria to become resistant. At the same time, drug-resistant infections acquired in hospitals kill 70,000 people a year. The problem is so dire that the Obama administration is paying drug companies to develop new antibiotics, and some groups want to test them directly on sick people to speed approval. While many physicians try to limit antibiotic use on sick patients to slow the spread of resistance, livestock growers can buy antibiotics over the counter at a feed store. Many hospitals have implemented antimicrobial stewardship programs, in which every milligram of antibiotic use is scrutinized," said Dr. Tom Newman, a professor of epidemiology and biostatistics at UCSF. About once a month, Brad Spellberg, an infectious disease researcher at Harbor-UCLA Medical Center, said he sees patients with abdominal or urinary tract E. coli infections that resist all oral antibiotics. Doctors are down to "one or two last-ditch IVs," or intravenous administration of antibiotics against some bacteria.