A potentially deadly bacteria is responsible for one in five sore throats in young adults, a new study suggests.
Patients with this bacteria - Fusobacterium necrophorum - can get negative results on a strep test, but be at risk of an abscess that blocks the airway, researchers report.
"If it looks like strep but it isn't strep, it could be this," said study author Dr. Robert Centor, a professor of medicine at the University of Alabama School of Medicine at Birmingham.
The need for antibiotics
Most sore throats get better without treatment, Centor said. But antibiotics should be prescribed when a patient "has a sore throat with fever, difficulty swallowing and swollen tonsils but a negative strep test," he said.
Read: 9 ways to prevent sore throats
In this study of young people aged 15 to 30, researchers found that more than 20 percent of the sore throats were caused by F. necrophorum - more than the number caused by group A streptococcal bacteria.
"The most serious complication from this bacteria is a disease called Lemierre's syndrome," Centor said.
"It can lead to serious infections in the lung, liver, brain and bone, and an estimated one of 20 patients who get this [Lemierre's] infection will die," he said. Fortunately, Lemierre's syndrome is extremely rare.
It infect teens and young adults
F. necrophorum appears to only infect teens and young adults, and about one in 400 of them will develop a serious complication, Centor said.
Researchers don't know why the infection is confined to this age group, or how this bacteria spreads, he added.
"We don't understand if it is contagious or if it's just there waiting for something to happen," he said.
Unlike strep throat, F. necrophorum cannot be diagnosed with a quick test, Centor said. That's because this bacteria doesn't grow when exposed to air, he explained.
Read: How to treat a sore throat
But like strep, F. necrophorum is easy to treat with penicillin, Centor said.
The report was published on February 16 in the Annals of Internal Medicine.
Dr. Jeffrey Linder, an assistant professor of medicine at Harvard Medical School, stressed that only a serious sore throat should be treated with antibiotics.
"I am concerned that this study is going to lead to more antibiotic prescribing than we have now," said Linder, author of an accompanying journal editorial.
Caution over antibiotics
Linder said many sore throats are caused by viruses, while antibiotics only work against bacterial infections.
Overuse of antibiotics leads to bacteria that are resistant to antibiotics, and the drugs can also cause serious side effects, he explained.
However, Linder agreed that a serious sore throat should not be ignored. Patients should see a doctor if their throat isn't getting better after four or five days, he said.
To estimate the prevalence of F. necrophorum, Centor's team studied 312 students who sought treatment for sore throat at the University of Alabama at Birmingham Student Health Clinic. The researchers compared them with 180 students who did not have a sore throat.
They found the F. necrophorum bacteria in 20.5 percent of patients with sore throat symptoms and about 9 percent of those without sore throats. It was the most common bacteria found, they noted.
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