Clinical Question: How accurate are the history and physical examination in the diagnosis of influenza?

Setting: Various (meta-analysis)

Study Design: Systematic review

Synopsis: Evidence on the accuracy of the history and physical examination in the diagnosis of influenza has not been systematically reviewed. The authors searched MEDLINE, bibliographies of identified studies, and the Database of Abstracts of Reviews of Effectiveness. They also contacted experts for articles reporting information on the accuracy of the history and physical examination in the diagnosis of influenza A and B. Two investigators separately reviewed all abstracts of identified studies, and a consensus approach was used to determine which articles would be included in the review.

Included articles were cohort studies (following patients identified at the initial time of illness) that used a reference laboratory test as the gold standard for the diagnosis of influenza. Although not specifically stated, it is likely that physicians performing the history and physical examination were unaware of the results of the reference standard. From an initial group of 97 studies, only seven met the inclusion criteria. Results were pooled for the diagnosis of influenza A or B.

The three signs or symptoms that were most useful for ruling in a diagnosis of influenza were rigors (positive likelihood ratio [LR+] = 7.2), fever and onset of symptoms less than three days before an office visit (LR+ = 4.0), and sweating (LR+ = 3.0). Symptoms that were helpful in ruling out influenza were having no systemic symptoms (negative likelihood ratio [LR–] = 0.36), the absence of coughing (LR– = 0.38), being able to cope with daily activities (LR– = 0.39), and not needing to be confined to bed (LR– = 0.50).

Bottom Line: Three signs or symptoms that are useful for ruling in a diagnosis of influenza are rigors, fever and onset of symptoms less than three days before an office visit, and sweating. Four symptoms helpful at ruling out influenza are an absence of systemic symptoms, an absence of coughing, no difficulty coping with daily activities, and not needing to be confined to bed. (Level of Evidence: 2b)