TORONTO: Coughing after a respiratory infection is common and, in most cases, will resolve with time - within eight weeks, according to researchers.

The team from the University of British Columbia in Canada said that coughs lasting longer than eight weeks need further assessment.

"Reassuring patients that post-infectious cough is time-limited and self-resolving is important and can reduce unnecessary and costly prescriptions, such as asthma puffers or antibiotics," said Dr. Kevin Liang, a family physician and clinical instructor in the Department of Family Practice at the University.

"Most postinfectious cough symptoms will improve without medication," Liang said.

In an article published in the Canadian Medical Association Journal, the researchers described that post-infectious coughs are common, affecting about 11 per cent to 25 per cent of adults after a respiratory infection and can last up to eight weeks.

Diagnosis requires an earlier respiratory infection and exclusion of other postinfectious cough mimics, such as asthma and chronic obstructive pulmonary disease. However, one must check for red flags like swallowing difficulty, excessive shortness of breath, and coughing up blood.

These may require investigation.

Red flags also include a history of recurrent pneumonia or an extended history of smoking, and coughs lasting longer than eight weeks need further assessment, the researchers said. Further, the team said that "there is no good evidence for a medication that works to stop post-infectious cough".

Evidence shows little benefit with inhalers or oral medications to treat a cough. These medications can be quite costly and cause unwanted side effects as well.

"Patient reassurance and education are critical. Clinicians should advise patients to arrange a follow-up appointment for further investigation if their cough has not resolved within eight weeks or if new symptoms appear," the researchers said.