Atlanta, GA—While healthcare focus has been zeroed in on COVID-19 in recent months, influenza is still circulating in the United States. The CDC reported in mid-March that laboratory-confirmed flu activity continued to decrease but reports of influenza-like illness activity increased.

In a study published in JAMA Network Open, CDC researchers looked at the types of respiratory and nonrespiratory diagnoses associated with influenza in hospitalized adult patients since the 2009 influenza pandemic.

The cross-sectional analysis of more than 80,000 adults hospitalized with laboratory-confirmed influenza between 2010 and 2018 in the U.S. found that 95% of patients had a respiratory diagnosis and 46% had a nonrespiratory diagnosis, including 5% with exclusively nonrespiratory diagnoses.

Noting that seasonal influenza virus infection is a major cause of morbidity and mortality, the study team used data from the U.S. Influenza Hospitalization Surveillance Network (FluSurv-NET) for the 2010-2011 through 2017-2018 influenza seasons. FluSurv-NET is a population-based, multicenter surveillance network including about 9% of the U.S. population. Patients are identified by practitioner-ordered influenza testing. Included in this study were adults hospitalized with laboratory-confirmed influenza.

The study defined acute respiratory or nonrespiratory diagnoses using the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) and International Statistical Classification of Diseases and Related Health Problems, 10th Revision (ICD-10) discharge diagnosis codes.

Of 89,999 adult patients hospitalized with laboratory-confirmed influenza in the database, 76,649—median age, 69 years; interquartile range, 55 to 82 years; 55% female—had full medical record abstraction and at least one ICD code for an acute diagnosis. Results indicate that 94.9% of patients had a respiratory diagnosis and 46.5% had a nonrespiratory diagnosis, including 5.1% with only nonrespiratory diagnoses.

The most common acute diagnoses were pneumonia (36.3%), sepsis (23.3%), and acute kidney injury (20.2%). Researchers also point out that fewer patients with only nonrespiratory diagnoses received antiviral therapy for influenza compared with those with respiratory diagnoses (81.4% vs. 88.9%; P < .001).

“Non-respiratory diagnoses occurred frequently among adults hospitalized with influenza, further contributing to the burden of infection in the United States,” the authors conclude. “The findings suggest that during the influenza season, practitioners should consider influenza in their differential diagnosis for patients who present to the hospital with less frequently recognized manifestations and initiate early antiviral treatment for patients with suspected or confirmed infection.”

The CDC estimates that 140,000 to 810,000 hospitalizations and 12,000 to 61,000 deaths among adult patients are attributable to influenza in the U. S. annually, depending on the season.

Nonrespiratory diagnoses of influenza tend to be underrecognized but could include acute myocardial infarction; seizures and other neurologic manifestations; acute kidney injury; and sepsis with influenza, according to the report, which adds that less common but important diagnoses that have led to hospitalization include encephalitis and acute myocarditis.

 « Click here to return to Weekly News Update.