Underdiagnosis of influenza virus infection in hospitalized older adults.

OBJECTIVE: To describe factors associated with provider-ordered influenza testing among hospitalized adults.

DESIGN: Information on patient demographics, symptoms, and provider-ordered influenza testing were collected by questionnaire and chart review. We conducted prospective laboratory-based surveillance using reverse-transcriptase polymerase chain reaction (RT-PCR), the gold-standard for diagnosis of influenza, to determine how patient characteristics and provider-ordered testing impacted accurate influenza diagnosis.

SETTING: One academic and three community hospitals in Davidson County, Tennessee, USA.

PARTICIPANTS: 1422 adults ages 18 years and older with acute respiratory illness or non-localizing fever.

MEASUREMENTS: We compared characteristics of participants with and without provider-ordered testing for influenza using the Wilcoxon test and Pearson's chi-square test. Multivariable logistic regression models identified factors predictive of provider-ordered influenza testing.

RESULTS: Overall 28% (399/1422) of participants had provider-ordered influenza testing. Patients who were tested were younger than those not tested (58 ± 18 years vs. 66 ± 15 years, p < 0.001) and more likely to have influenza-like illness (ILI, 71% vs. 49%, p < 0.001). ILI increased with decreasing age: 48% ≥ 65 years; 60% 50-64 years; and 63% 18-49 years. Among all patients, presence of ILI and younger age were independent predictors of provider-ordered testing. Among the 136 patients with RT-PCR confirmed influenza, ILI was the only significant predictor of provider-ordered testing (AOR 3.43, 95% CI 1.22-9.70).

CONCLUSION: Adults 65 years and older hospitalized with fever or respiratory symptoms during influenza season are less likely to have a provider-ordered influenza test than younger adults. Some, but not all, of this disparity is due to a lower likelihood of ILI presentation. Further strategies are needed to increase clinician awareness and testing in this vulnerable group. This article is protected by copyright. All rights reserved.