But the bacteria is not completely benign, said Lipsitch.

“It causes disease when it reaches a place where it doesn’t belong,” he said. “It travels from the upper respiratory tract to other places,” like the lungs, spinal cord, blood and ear.

He said that these infections can be fatal if left untreated, especially when they occur later in life.

Lipsitch also said the rise of drug resistance is not restricted to this bacteria.

“Resistance to penicillin... appeared within months of its first use. Drug resistance has been around as long as clinical use of antibiotics,” he said.

But according to Lipsitch, the genes responsible for drug resistance are much more ancient.

Since most of the antibiotics used today are derived from plants and other organisms that use them to naturally defend themselves from infection, bacteria have had plenty of time to develop resistance to these chemicals, he said.

McCormick said that the recent rise in resistance is because antibiotics are increasingly misprescribed, offered to patients for viral infections or other illnesses—for which antibiotics are ineffective.

There is hope that a vaccine released in 2000—effective against most of the strains with a high percentage of antibiotic resistance—will help to reduce the number of untreatable cases, she said.

“If most of the population is vaccinated, fewer people will be infected, and there will be a decrease in the number of people infected by resistant strains. There will be a decrease in the percentage who have resistant bacteria,” McCormick said.

However, her study found that the percentage of bacteria resistant to antibiotics will continue to increase so long as antibiotics are prescribed as frequently as they are now.

Lipsitch said that the prospects for a solution are slim.

“In the short term, the vaccine should reduce the number of resistant infections,” he said. “In the long term, bacteria will be smart enough to reestablish their resistance to treatment.”