Diagnosis of influenza in the community - Relationship of clinical diagnosis to confirmed virological, serologic, or molecular detection of influenza

Background: Successful treatment of influenza depends on an accurate diagno sis of the illness and prompt intervention. However, there is a lack of dat a comparing clinical diagnosis vs laboratory diagnostic techniques. Objective: To compare the clinical diagnosis of community cases of influenz a with various laboratory diagnostic techniques including multiplex, revers e transcription polymerase chain reaction. Methods: Clinical diagnosis, viral isolation, hemagglutinin inhibition sero logy, and multiplex, reverse transcription polymerase chain reaction were u sed to diagnose influenza in patients enrolled in international phase 3 stu dies designed to investigate the efficacy and safety of an antiinfluenza dr ug (inhaled zanamivir). Patients clinically diagnosed with influenza were e nrolled at centers across North America and Europe. Results: A total of 791 (77%) of 1033 patients with laboratory results from all 3 methods were confirmed positive for influenza by 1 or more test resu lts. For 692 patients (67%), the results of all 3 tests agreed. Total sympt om scores at baseline showed a significant association toward greater sever ity of symptoms with an increasing number of positive test results (P < .00 1). An increasing number of positive test results also showed a significant correlation with a longer time to alleviation of symptoms of influenza in the placebo group (P=.001). Conclusions: During a time when influenza was known to be circulating and c linical diagnostic criteria were applied, diagnosis of influenza in these t rials was accurate in approximately 77% of adults on clinical grounds alone . This highlights the need for primary care physicians to be alerted to cir culating influenza and to be aware that presentation with cough and fever p rovide the most predictive symptoms.