Identifying influenza

The Centre for General Practice at the University of Antwerp, Belgium, has researched how to differentiate influenza from other illnesses. The aim was to improve the accuracy of diagnosis in an epidemic.

For five winters, 138 GPs collected information from patients with influenza-like illnesses. On average the patients presented within two days of becoming unwell. They complained of a median of nine symptoms, such as fever, muscle pain and headache.

The GPs took oropharyngeal and nasopharyngeal swabs from 4597 patients. Overall, 53% of the swabs were positive for influenza. During an epidemic 64% of the swabs were positive, compared with 25% before or after an epidemic. 

The researchers combined laboratory findings with clinical features to calculate the likelihood of a patient having influenza. Features favouring a diagnosis of influenza include contact with an infected person, loss of appetite, cough and a temperature over 37.8°C.