I worry about a lot of things that could go wrong if I'm taken to a hospital, but until today this hasn't been one of them: Hospitals are routinely running short of critical antibiotics, often for months at a time.

When Larissa May, an associate professor of emergency medicine at George Washington University, and a team of researchers checked, they found that hospitals across the country ran short of 148 anti-bacterial drugs over a 13-year period, from 2001 to 2013. The average time without a drug was nearly nine months (injectable drugs generally ran short for even longer periods than medications taken by mouth). Thirty-two of the medications ran short more than once, including one, Meropenem, which was short seven different times for a total of 1,114 days.

These were not exotic pharmaceuticals that were needed now and then. We're talking about front-line antibiotics used to treat various infections, including multidrug-resistant bacteria such as MRSA, carbapenem-resistant Enterobacteriaceae and clostridium difficile. In some cases, the only drug available against a certain infection ran short.

There's no question that "these shortages often impact clinicians' ability to treat infections," May wrote. In a 2010 survey, clinicians reported "adverse outcomes" because of drug shortages in 20 percent of their cases. May's research team did not look for fatalities, so it's unclear whether any resulted from a drug shortage.

"It's pretty scary, really," May told me in an interview. "There are some infections for which there are very limited alternatives, or no alternatives for that drug." So in some cases, the drug cupboard is simply bare, she said.

We've all  heard of drug-resistant bacteria and the problem of over-prescribing antibiotics. But I doubt the average person understands it's possible to be admitted to a hospital for a serious infection and have the doctor say the pharmacy is simply out of the drug he needs. But it happens all the time, according to the data May's team compiled from a database run by the University of Utah Drug Information Service. The study was published in the journal Clinical Infectious Diseases.

For example, injectable doxycycline, used to treat Lyme disease, pneumonia and urinary tract infections, ran short three times during the study period, for a total of 1,515 days.

Vancomycin, used to treat severe skin infections and endocarditis, among other conditions, ran short three times for 373 days and was still on shortage when the study ended.

The Food and Drug Administration defines a drug shortage as a period when total supply of various versions of antibiotics is inadequate to meet projected demand "at the user level." Individual hospitals may or may not have some on hand, depending on recent use.

There are several reasons why this happens, according to the study. Drug companies have been merging, prompting consolidation of their manufacturing facilities. The profit margin for antibiotics is thin, providing little incentive for those companies to come out with new drugs. Some drugs, such as one for the treatment of Pneumocystis pneumonia, are produced by a single manufacturer.

Communication between hospital pharmacies and drug manufacturers also needs improvement, the research concludes. "In half of cases, physicians and nurses learn about drug shortages from pharmacy staff, often when the pharmacy is unable to dispense the medication," they wrote.

May said she is hopeful that a new federal government program to create incentives for development of new antibiotics will be helpful, and she suggested that manufacturers be required to alert hospitals when drugs are running short.