Flu Testing
Corey Diamond, PharmD
A new analysis, published February 2022 in Chest by Deshpande and colleagues, looked at the relationship between how often patients were tested for influenza and their clinical outcomes. The analysis, based on a robust multihospital cohort, focused specifically on community-acquired pneumonia (CAP) patients, underscoring several key findings between flu testing tendencies and their effects on a patients’ mortality and morbidity. The study supports the hypothesis that routine flu testing in CAP patients increases the likelihood of optimal treatment and reduced mortality.
Study goal
The research team conducted a retrospective cohort analysis using the Premier Database, which included aggregated patient information from more than 600 hospitals in the United States. The analysis included over 160,000 patients who had an ICD-9 primary diagnosis for pneumonia or a secondary diagnosis of pneumonia with influenza, sepsis, or respiratory failure between July 1, 2010, and June 30, 2015, from 179 hospitals within the database.
The researchers investigated several relationships between the total yearly fraction of patients tested for influenza A or B within 3 days of hospitalization and patients with positive, negative, or no test results. They were mainly interested to see if testing CAP patients for flu was associated with optimal antiviral treatment and shorter antibiotic courses. Additionally, if a correlation was affirmed, they wanted to investigate an association between early administration of antivirals and better clinical outcomes among those CAP patients who tested positive.
Implications
The current literature is inconsistent in demonstrating a positive correlation between routine flu testing and clinical benefit, particularly among patients presenting with CAP. Due to the absence of widespread testing protocols for flu, many hospital patients who are admitted for acute respiratory illness go undiagnosed, leading to poorly optimized anti-infective therapy.
The 2018 Infectious Diseases Society of America influenza guidelines recommend that all hospitalized patients presenting with acute respiratory illness or acute worsening of chronic cardiopulmonary disease be tested for influenza during flu season. Despite this, the CDC FluServ-NET reported that between the years of 2010 and 2012 only about a third of patients presenting with respiratory symptoms were tested for flu.
Effect on clinical outcomes
One of the most critical components to flu treatment is early administration of a neuraminidase inhibiter—principally oseltamivir—and the results of the analysis appear to reaffirm this. Most patients who received oseltamivir on hospital day 1 were also tested for flu. By Day 14, among patients who tested positive for flu, patients who received early oseltamivir—defined as those given oseltamivir on Day 1—were 25% less likely to die relative to those not receiving oseltamivir early on in therapy or at all. Additionally, early oseltamivir therapy was associated with a reduction in ICU transfer, invasive mechanical ventilation, and vasopressor support by 36%, 56%, and 57%, respectively.
Effect on stewardship
In terms of antimicrobial stewardship, the effect of flu testing on reducing antibiotic use was statistically significant. On Day 1 of admission, antibiotics were given to 82.1% of patients who tested positive for flu versus 99.9% not tested. The effect became more pronounced by Day 3, with 76.6% of flu-positive patients receiving antibiotics versus 90.8% of pneumonia patients not tested.
However, the clinical significance in the reduction in antibiotic use is perhaps beneficial on a macro scale only. “Influenza testing seems only modestly effective in reducing antibiotic use,” the authors stated. “Even patients testing positive for influenza were likely to receive antibiotics, albeit with shorter courses. Testing more patients, especially during flu season, could slightly decrease antibiotic use at the population level.”
Who needs to be tested versus who is actually being tested?
Among the CAP patients included in the 5-year analysis, only 23% were tested for flu. In particular—among that 23%—those admitted from skilled nursing facilities (SNFs) were statistically more likely to test positive for flu, yet SNF-admitted pneumonia patients, overall, were statistically less likely to receive a flu test. This analysis would appear to assert that there is not only substantial room for improvement in flu testing practices, but also a large benefit to gain from more frequent testing from both a patient and antimicrobial stewardship perspective.
“If our findings regarding early oseltamivir treatment are confirmed,” the authors concluded, “then testing and treating additional patients could save lives and reduce resource utilization.” ■