A systematic review including 6 studies on history and physical examination was abstracted in DARE. There was one retrospective pooled analysis of clinical trials (n=3,744), one RCT of influenza vaccine (n=1,838) and four prospective diagnostic cohort studies (n=1,582). In an unselected population, the absence of fever (LR 0.40, 95% CI: 0.25, 0.66), cough (LR 0.42, 95% CI: 0.31, 0.57), or nasal congestion (LR 0.49, 95% CI: 0.42, 0.59) decreased the likelihood of influenza. In studies limited to patients aged 60 years and older, the combination of fever, cough and acute symptom onset (LR 5.4, 95% CI: 3.8, 7.7), fever and cough (LR 5.0, 95% CI: 3.5, 6.9), fever alone (LR 3.8, 95% CI: 2.8, 5.0), malaise (LR 2.6, 95% CI: 2.2, 3.1) and chills (LR 2.6, 95% CI: 2.0, 3.2) increased the likelihood of influenza. The presence of sneezing in these patients made influenza less likely (LR 0.47, 95% CI: 0.24, 0.92).
Comment: The quality of evidence is downgraded by inconsistency (variability in results across studies).
Clinical comment: Clinicians should use timely epidemiologic data to ascertain if influenza is circulating in their communities, then either treat patients with influenza-like illness empirically or obtain a rapid influenza test to assist with management decisions.