Although influenza is a commonly encountered condition in primary care, and diagnosis is increasingly important given the availability of new treatments, there has been no systematic review of the evidence on clinical diagnosis. Methods: This was a systematic review of the literature with meta-analysis where appropriate. We included cohort studies and randomized trials that compared the history and physical examination with a reference laboratory test for the diagnosis of influenza A and/or B.

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... he primary outcomes were the sensitivity, specificity, likelihood ratios, and area under the receiver-operating characteristic (ROC) curve. Results: Seven studies reported the sensitivity and specificity for a total of 59 variables. We combined studies of influenza A or B alone with those of influenza A and B. Rigors [likelihood ratio (LR) ؉7.2], the combination of fever and presenting within 3 days of the onset of illness (LR ؉4.0), and sweating (LR ؉3.0) were best at ruling-in influenza when present. When absent, the following decreased the likelihood of influenza: any systemic symptoms (LR ؊0.36), coughing (LR ؊0.38), not being able to cope with daily activities (LR ؊0.39), and being confined to bed (LR ؊0.50). Cough, nasal congestion, and fever (subjective or objective) had the highest calculable areas under the ROC curve. Conclusions: Individual signs and symptoms are of limited value for the diagnosis of influenza. Development of clinical decision rules that systematically combine symptoms may be a more useful strategy. (J Am Board Fam Pract 2004;17:1-5.)