Clinical diagnosis of influenza virus infection: evaluation of diagnostic tools in general practice

Background: With the development of new antiviral agents for influenza, the urge for rapid and reliable diagnosis of influenza becomes increasingly im portant. Respiratory virus infections are difficult to distinguish on clini cal grounds General practitioners (GPs) however still depend on their clini cal judgement, Aim: To evaluate the importance of clinical symptoms in the diagnosis of in fluenza virus infection, Design of study: A multicentre questionnaire study. Setting: Eighty-one patients from 14 general practices. Method: Patients with fever and at least one constitutional symptom and one respiratory symptom were included. A questionnaire with the medical histor y and clinical symptoms was, completed and a combined nose-throat swab was taken. Virus culture, rapid culture, and polymerase chain reaction (FCR) am plification, were performed on each specimen, Multivariate analysis was use d to obtain the best predictive model, Results By using FCR, an increase was seen in the detection of the viral pa thogens compared with the results of culture. in 42 out of 81 patients PCR was positive for influenza. A positive predictive value (PPV) of 75% was ob served for the combination of headache at onset, feverishness at onset, cou gh, and vaccination status during the period of increase influenza activity . Criteria used by the ICHPPC-2 resulted in a PPV of 54%. The PPV for diagn osis made by the GP was 76%. Conclusion: Although influenza is difficult to diagnose on clinical grounds , the GPs in this study were able to diagnose influenza as such more accura tely on their judgement than by the other criteria.