Several times a week Brad Spellberg struggles with a difficult decision. A patient stumbles into his emergency room in southern California suffering from familiar symptoms: pressure when she urinates, pain in her side, fever and nausea. Based on these clues Spellberg can quickly diagnose the problem as a kidney infection, but the trouble lies in deciding what he should do next. He knows the patient is hurting and of course he wants to help, but more than his patient’s health hangs in the balance.

Like any emergency room clinician Spellberg has two disparate options. The first is to treat the patient with a powerful antibiotic called carbapenem, administered intravenously. It would wipe out a variety of bacteria that might be causing the infection, but there is a catch. Deploying this precious resource may make it less likely he can use it to treat a future patient. The drug would kill susceptible bacteria but it would also fuel resistance by allowing the few microbes that are able to survive carbapenem to thrive and multiply. Spellberg’s second option is to send the patient home with a lower-level class of drug, a quinolone. The stakes of his decisions are high. If a relatively mild bacterium is behind the patient’s infection, a quinolone would neutralize it and the patient would recover. But if the infection is caused by a drug-resistant pathogen, the patient would not recover without carbapenem and the untreated infection may worsen.

Spellberg’s catch-22 comes down to an issue of timing. He will not know exactly what bug is causing the patient’s infection for several days because there are no fast, cheap diagnostic tests available. So it will take three days for lab workers to identify the patient’s assailant. Spellberg cannot wait that long to make his choice. His dilemma, sadly, is not uncommon. Across the country doctors are struggling with the same issues he faces as the chief medical officer at the Los Angeles County + University of Southern California Medical Center.