Context Influenza vaccination lowers, but does not eliminate, the risk of influenza.
Making a reliable, rapid clinical diagnosis is essential to appropriate patient
management that may be especially important during shortages of antiviral
agents caused by high demand.
Objectives To systematically review the precision and accuracy of symptoms and
signs of influenza. A secondary objective was to review the operating characteristics
of rapid diagnostic tests for influenza (results available in <30 min).
Data Sources Structured search strategy using MEDLINE (January 1966-September 2004)
and subsequent searches of bibliographies of retrieved articles to identify
articles describing primary studies dealing with the diagnosis of influenza
based on clinical signs and symptoms. The MEDLINE search used the Medical
Subject Headings EXP influenza or EXP influenza A virus or EXP influenza A virus human or EXP influenza B virus and the Medical
Subject Headings or terms EXP sensitivity and specificity or EXP medical history taking or EXP physical examination or EXP reproducibility of
results or EXP observer variation or symptoms.mp or clinical signs.mp or sensitivity.mp or specificity.mp.
Study Selection Of 915 identified articles on clinical assessment of influenza-related
illness, 17 contained data on the operating characteristics of symptoms and
signs using an independent criterion standard. Of these, 11 were eliminated
based on 4 inclusion criteria and availability of nonduplicative primary data.
Data Extraction Two authors independently reviewed and abstracted data for estimating
the likelihood ratios (LRs) of clinical diagnostic findings. Differences were
resolved by discussion and consensus.
Data Synthesis No symptom or sign had a summary LR greater than 2 in studies that enrolled
patients without regard to age. For decreasing the likelihood of influenza,
the absence of fever (LR, 0.40; 95% confidence interval [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) were the only findings that had summary LRs less than 0.5. In studies
limited to patients aged 60 years or older, the combination of fever, cough,
and acute 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 to the greatest degree. The presence of sneezing among older
patients made influenza less likely (LR, 0.47; 95% CI, 0.24-0.92).
Conclusions Clinical findings identify patients with influenza-like illness but
are not particularly useful for confirming or excluding the diagnosis of influenza.
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