Antibiotics don't help fight most sinus infections, although doctors routinely prescribe them for that purpose, according to a US study.

Researchers whose work was published in the Journal of the American Medical Association found that antibiotics didn't ease patients' symptoms or get them back to work any sooner than an inactive placebo pill.

Antibiotics are known to fuel the evolution of drug-resistant bacteria and experts have grown increasingly worried about overuse.

This is a particular concern with sinus infections, because doctors can't tell if the disease is caused by bacteria or a virus, in which case antibiotics are useless.

'There is not much to be gained from antibiotics,' said Jane Garbutt of Washington University School of Medicine in St Louis, who led the study.

'Rather than give everybody an antibiotic hoping to find the (patients) with bacteria, our findings would suggest refraining from antibiotics and doing what we call watchful waiting,' she told Reuters Health.

That involves keeping an eye on patients to see if they get better, but not using drugs other than over-the-counter painkillers.

People with sinus infections, also called acute sinusitis, have lasting and severe cold-like symptoms such as a runny nose and pain around the eyes, nose or forehead.

'It's the fifth most common reason antibiotics are prescribed for adults. It's hard for doctors not to give an antibiotic because patients are so miserable, and we don't have anything else to give them,' said Garbutt.

Garbutt and her colleagues used official US guidelines to identify patients with sinus infections. They randomly assigned 166 adults to either placebo pills or a 10-day treatment with the antibiotic amoxicillin.

Based on patient ratings on a symptom scale known as the modified Sinonasal Outcome Test-16, or SNOT-16, the researchers found little difference between the two patient groups.

Using the scale, where 0 equals 'no problem' and 3 a 'severe problem,' the antibiotic group rated their symptoms at 1.12 after three days, while the placebo group averaged 1.14.

After seven days, there were signs of benefit from the antibiotic, but the effect was small and had vanished another three days later.

After 10 days, 78 percent of the people on antibiotics and 80 percent of the placebo-treated people said they felt a lot better or no longer had symptoms.

Fewer than two percent of sinus infections are bacterial, said Anthony Chow, an expert in infectious diseases at the University of British Columbia in Vancouver, Canada.

'Most cases are viral, and the vast majority doesn’t require antibiotics,' he said. 'Antibiotics have been abused, so there is a need to be more cautious in prescribing them and to hold back.'

But he said that antibiotics still do have a place and recently chaired a committee at the Infectious Diseases Society, which has developed guidelines to help spot infections that are more likely to be bacterial.

Those guidelines, still in press, recommend treating only patients whose symptoms last for at least 10 days and keep worsening, who are severely sick with high fever and other symptoms, or who improve and then get worse again. - Reuters