Doctors may be overprescribing antibiotics for sinus infections that are often caused by viruses, according to a new U.S. study.

Viruses are the most common cause of acute sinus infections, but antibiotics do not work against viruses.

Yet antibiotics were prescribed for about 82 per cent of acute sinus infections and nearly 70 per cent of chronic sinus infections, a study of two national surveys in the U.S. showed.

"The use of prescription antibiotics far outweighs the predicted incidence of bacterial causes of acute and chronic rhinosinusitis," Hadley Sharp of the University of Nebraska Medical Center in Omaha and her colleagues concluded in this week's issue of Archives of Otolaryngology — Head & Neck Surgery.

Sinus infection, technically called rhinosinusitis, is an inflammation of the sinus cavities next to the nasal passages.

The infections are considered acute when symptoms last up to four weeks, and chronic if they last for 12 weeks or longer. For acute sinus infections, the treatments of choice are watchful waiting, irrigation with salt water, use of a decongestant or appropriate antibiotics.

Prescriptions demanded

About two-thirds of patients with sinus symptoms expect and receive an antibiotic, and up to one-fifth of antibiotic prescriptions for adults in the U.S. are written for sinus infections, the team said.

Infectious agents such as bacteria and viruses are usually thought to cause the acute infections. Allergies and facial anatomy such as a deviated septum may contribute to chronic cases, and hormonal changes are also suspected.

Antibiotics were the most frequently recommended medications for both acute and chronic sinus infections, followed by antihistamines, nasal decongestants, corticosteroids, cough medicines, the researchers found.

It is possible that doctors may prescribe antibiotics to treat secondary infections. Physicians may also think the drugs work based on their past experience, when, in fact, the symptoms may have cleared up on their own thanks to the patient's immune system.

"The vast use of these agents makes the statement that they seem to be effective in reducing symptoms or preventing relapse, or they would have been abandoned," the study's authors said.

Nasal and inhaled corticosteroids were also more prescribed more often than published studies imply is needed, the team said, but since steroids are used to treat allergic rhinosinusitis, overuse is unclear.