Doctors need to give antibiotics to more than 12,000 people with acute respiratory infections to prevent just one of them from being hospitalized with pneumonia, according to a new study.
And that small benefit is outweighed by the very real risks that go along with antibiotics - both from serious side effects and the promotion of resistant "superbugs," researchers say.
"This study is actually reassuring to both doctors and patients. What we said all along (is) that antibiotics are not helpful or not needed for the upper respiratory infections - I think this supports that," said Dr. Sharon Meropol, the study's lead author, from Rainbow Babies and Children's Hospital in Cleveland.
The problem of microbial resistance to drugs is growing, and research shows that overuse of antibiotics is a major contributor. One recent study found, for example, that resistant superbugs proliferated after cold-and-flu season, suggesting they had been fed by seasonal antibiotic use.
Other studies have shown that many of the respiratory infections for which doctors give antibiotics are caused by viruses, against which antibiotics are no use.
When a respiratory infection is caused by bacteria, though, antibiotics can help, and the drugs may prevent a serious chest infection from becoming full-blown pneumonia, which is especially dangerous for the elderly and young children.
To gauge the relative risks and benefits of using antibiotics to treat respiratory infections in adults outside the hospital setting, Meropol and her fellow researchers from the University of Pennsylvania in Philadelphia looked at UK data on more than 1.5 million visits to doctors by more than 800,000 people with respiratory infections over 20 years.
About 65 per cent of the patients, who were all over age 18, received antibiotics for their infections, Meropol's team reports in the Annals of Family Medicine.
The patients were tracked over 15 days after their initial doctor visit to see how many were admitted to the hospital with pneumonia or a serious adverse event that could be a reaction to the drugs, including heart problems, diarrhoea, liver or kidney toxicity and seizures.
Overall, there were 296 people admitted to the hospital with pneumonia within 15 days of the first doctor visit. That worked out to about 22 people admitted to the hospital with pneumonia per 100,000 office visits if they did not get an antibiotic - compared to about 18 people per 100,000 visits among those treated with antibiotics.
Meropol said that means 12,255 or more people would have to be treated with antibiotics to prevent one person from being hospitalized.
"There is a benefit, but it really is vanishingly small," said Dr. Jeffrey Linder, who was not involved in the study but has studied antibiotic prescribing.
The researchers also found little difference between the two groups in the number of serious adverse events they experienced. There were 8.5 serious events per 100,000 office visits among patients who took antibiotics and 7.75 events per 100,000 visits among those who didn't take the drugs.
Linder, an associate professor at Brigham and Women's Hospital and Harvard Medical School in Boston, told Reuters Health that previous research based on US data has found much higher rates of serious side effects with antibiotic use. People taking them have a one in 1,000 chance of going to the emergency room with an adverse event, he said, which translates to 100 per 100,000.
The new study did find a large difference in the number of minor adverse events that sent people back to their doctors after taking antibiotics.
There were about 112 more minor adverse events per 100,000 office visits among those who took antibiotics, compared to those who did not. That number doesn't include minor events that people may have treated at home without returning to the doctor.
"We did find a lot more minor events, which may not have always been reported. People may not have gone for a rash or diarrhoea," Meropol said.
Linder said the message regarding antibiotics is still the same - that they should only be prescribed for a minority of sinus and ear infections, strep throat and pneumonia, but not for most other common respiratory infections.
"The risk-benefit is just not there. I think the message doesn't change, and this doesn't even factor in the risk of antibiotic resistance," he said.