Older Adults Undertested, Underdiagnosed with the Flu

Hospitals around the nation are seeing high volumes of patients with the flu this season. A new study, published online Jan. 17 in the Journal of the American Geriatrics Society, shows that older adults hospitalized with fever or respiratory symptoms during influenza seasons are less likely to have a provider-ordered flu test, compared to younger patients.

“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,” write the authors led by Lauren Hartman, M.D., from Vanderbilt University in Nashville, Tenn.

Older adults are disproportionately hospitalized for the flu and existing evidence shows that early diagnosis and treatment improves outcomes. The U.S. Centers for Disease Control and Preventions says that a total of 8,990 laboratory-confirmed influenza-associated hospitalizations were reported between Oct. 1, 2017, and Jan. 13, 2018. The overall hospitalization rate was 31.5 per 100,000 people. The highest rate of hospitalization is among adults 65 years and over (136.5 per 100,000), followed by adults aged 50 to 64 years (33.2 per 100,000) and then children aged 0 to 4 years (22.8 per 100,000).

Vanderbilt University researchers assessed influenza testing among 1,422 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 prospectively performed reverse-transcriptase polymerase chain reaction (RT-PCR) influenza testing for all patients, even if the patients’ providers had not ordered it. The researchers 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.

The researchers found that over the study period, providers requested tests for just over one-fourth of patients (28 percent). Of those patients with tests ordered, patients who were younger were significantly more likely to have provider-ordered testing were younger than untested patients (average age, 58 years for tested patients versus 66 years for untested patients). Part of this difference was explained that tested patients were more likely to have flu-like symptoms (e.g. fever, cough, and/or sore throat), which decreased with age.

RT-PCR testing identified flu in 10 percent of patients (n=136), but of those patients with confirmed flu, 43 percent did not have test orders placed by their providers.  Patients receiving care in the academic hospital were more likely to have provider-ordered influenza tests (41 percent versus 20 percent in community hospitals). The 450 provider-ordered tests were primarily for antigen detection (97.0 percent), 7.3 percent were for viral culture, and 8.5 percent were for RT-PCR.

“The challenge of influenza diagnosis in hospitalized older adults is to not only identify cases clinically, but select an appropriate sensitive diagnostic test such as RT-PCR,” write Hartman and colleagues.

Takeaway: Older, hospitalized patients are undertested and underdiagnosed with the flu. Furthermore, when testing is ordered it is most often not sensitive diagnostic tests, like RT-PCR.