Doctors Underdiagnosing Flu Among Older Patients

Ricki Lewis, PhD

January 19, 2018

Adults aged 65 years or older presenting at hospitals with influenza-like illness (ILI) during the winter months were less likely to have had a provider-ordered influenza diagnostic test than were younger adults, according to findings published online January 18 in the Journal of the American Geriatrics Society.

Accurate diagnosis of influenza can lead to earlier antiviral treatment, minimizing individual suffering as well as limiting spread of the infection. Such tests include reverse transcriptase polymerase chain reaction (RT-PCR) to detect viral RNA, rapid antigen detection, and viral culture.

Older adults have the highest rates of hospitalization and death due to influenza, yet several factors may affect presentation. These include effects of comorbidities, cognitive deficits that alter perception or reporting of symptoms, immune senescence, and age-associated lower core body temperature influencing assessment of fever. 

Lauren Hartman, MD, from the Department of Medicine at Vanderbilt University School of Medicine in Nashville, Tennessee, and colleagues investigated influenza testing among 1422 adults hospitalized with acute respiratory illness or nonlocalizing

fever at four hospitals (one academic and three community facilities) in Tennessee between November 2006 and April 2012. They used a prospective, laboratory-based surveillance approach, including information from patient questionnaires and charts.

The researchers performed RT-PCR influenza testing for all patients, even if the patients' providers had not ordered that or other tests to confirm influenza. The investigators then compared demographic and clinical characteristics of patients whose providers had ordered testing with those of patients for whom laboratory-based diagnostic tests had not been ordered.

Overall, providers requested tests for just 28% (399 of 1422) of patients. Patients whose providers ordered testing were younger than untested patients (average age, 58 ± 18 years vs 66 ± 15 years; P < .001) and were more likely to have symptoms (71% vs 49%; P < .001).

ILI symptoms, including fever, cough, and/or sore throat, decreased with increasing age: 63% for patients aged 18 to 49, 60% for those aged 50 to 64, and 48% for those aged 65 or older. For all patients, ILI and younger age were independent predictors of provider-ordered testing.

RT-PCR testing identified 136 of the 1422 (10%) patients as having influenza. Of those, 59 (43%) had not been tested by their providers.

ILI was the only significant predictor of provider-ordered testing (adjusted odds ratio, 3.43; 95% confidence interval, 1.22 - 9.70). Month of illness, sex, and race were not significant predictors.

Of participants receiving care in the academic hospital, 41% (231 of 561) had provider-ordered influenza testing compared with only 20% (168 of 861) of patients in the community setting. Of the 450 provider-ordered tests, 387 (97.0%) were antigen detection, 29 (7.3%) were viral culture, and 34 (8.5%) were RT-PCR based.

Of the patients for whom providers had ordered testing, 8% (32 of 399) had clinical laboratory-confirmed influenza. They were 2% (32 of 1422) of the total population. Patients whose providers had ordered testing were more likely to receive antiviral agents (6.8% vs 0.2%; P < .001).

The investigators conclude, "Despite being at high risk for morbidity and mortality from influenza virus infection and sequelae, hospitalized older adults were tested for influenza less often than their younger counterparts, with testing performed in a minority of patients."

The apparent age disparity in diagnostic testing may reflect the different timetable of influenza symptoms in patients over age 65. While early symptoms may be tamer than in younger individuals, perhaps influencing decisions not to test, "older adults

may present later in illness with complications associated with influenza, leading clinicians to forego testing and treatment" of influenza and focus on the complications, the researchers hypothesize.

"Further strategies are needed to increase clinician understanding of the challenges in clinically identifying influenza in older adults, as well as the limitations of diagnostic tests, to better diagnose and treat cases of influenza in this vulnerable population," they advise.

A limitation of the study is applicability to other healthcare settings, such as urgent care clinics.

One coauthor has received research funding from Sanofi Pasteur, MedImmune, and Gilead and has served as an advisor for VaxInnate and Sequirus. Another coauthor has received research funding from MedImmune. Dr Hartman and the other authors have disclosed no relevant financial relationships.

J Am Geriatr Soc. Published online January 18, 2018. Abstract

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