At least 2 million Americans become infected every year with bacteria that are resistant to antibiotics. At least 23,000 people die as a direct result of these infections.

Public health officials blame much of the problem on overprescribing. But a look at where all those antibiotics are prescribed shows big differences. On average, people living in the South are given more antibiotics than people in other parts of the country. By contrast, people living in western states have the lowest rates overall.

Unless doctors and others change the way antibiotics are used, public health officials worry that even minor infections could become dangerous and that clinicians will lose their ability to treat cancer, transplant organs and save victims of burns and traumas.

Worldwide, antibiotic-resistant bacteria is already implicated in at least 700,000 deaths annually, and if trends continue, some estimate that death toll could skyrocket to 10 million a year by 2050.

Chinese and British researchers reported recently that they have found a strain of Escherichia coli that is resistant to colistin, the antibiotic of last resort for gram-negative bacteria such as E. coli. Those bacteria were found in pigs, raw pork meat and in a small number of people in China -- news that the head of the Centers for Disease Control and Prevention calls alarming.

"We are holding onto our last antibiotics by a thread," director Tom Frieden said, "and the new study shows that this thread  has already been cut for some patients and makes expansion of programs to protect patients and antibiotics even more urgent."

In the United States, CDC estimates that about 50 percent of antibiotic prescriptions written in outpatient settings, such as primary care offices and clinics, are unnecessary.

The map below shows how prescribing rates differ by geography. West Virginians had the highest antibiotic-prescribing rate in 2014, at 1.24 per person, more than double the rate for Alaskans.

According to the Pew Charitable Trust, 45 percent of all antibiotics prescribed in outpatient settings in 2013 were written by primary care physicians, including family practice doctors, pediatricians and internal medicine doctors. They wrote prescriptions for more than 120 million courses of antibiotics -- an average of 512 prescriptions each.

Physician assistants and nurse practitioners accounted for 18 percent of antibiotics prescribed in these settings, followed by dentists at 9 percent; emergency medicine providers at 5 percent and dermatologists at 3 percent.

Read more: