Flu Linked to Respiratory and Non-Respiratory Diagnoses

Eric Chow, MD, MS, MPH

Influenza (flu) virus infections could be associated with respiratory and non-respiratory diagnoses, according to new research.

The findings highlighted the broad scope of flu and infection burden.

Eric Chow, MD, MS, MPH, and a team of investigators sought to examine the respiratory and non-respiratory diagnoses reported for adults hospitalized with laboratory-confirmed flu between 2010-2018 in the US. Chow, from the Influenza Division of the National Center for Immunization and Respiratory Disease with the US Centers for Disease Control and Prevention, and colleagues used data from the US Influenza Hospitalization Surveillance Network from the 2010-2011 through 2017-2018 flu seasons.

The team included patients >18 years old who were hospitalized with laboratory-confirmed flu during the study period. Laboratory-confirmed flu was defined as infection within 14 before or 3 days of less after hospital admission based on a positive test of reverse transcription-polymerase chain reaction, rapid antigen assay, direct or indirect fluorescent staining, or viral culture.

Trained officers abstracted demographic data; chronic medical conditions; clinical course and outcomes; and discharge summary data from each patient’s medical record.

During the study period, 89,999 adults (median age, 69 years old; interquartile range, 54-81 years old; 55% female) had laboratory-confirmed flu in the database. Of the adults, 80,261 were available for analysis, with 81.8% having >1 ICD code. Nearly 87% had a pneumonia and flu code and 98.1% had a respiratory and circulatory code.

Among the adults available, 95.6% (median age, 69 years old; interquartile range, 55-82 years old; 55% female) had >1 acute diagnosis. Almost half had received a seasonal flu vaccine for the corresponding year and 88.5% received antiviral treatment for flu during their hospitalization.

Of the patients with an acute diagnosis, 94.9% had >1 acute respiratory diagnosis and 46.5% had >1 acute non-respiratory diagnosis—5.1% had only acute non-respiratory diagnoses.

For the nearly 95% of patients with >1 acute respiratory diagnosis, 43.3% had underlying respiratory comorbidities and 51.3% were current or former tobacco users. Those with only acute non-respiratory diagnoses had a significantly higher frequency of underlying comorbidities than those with respiratory diagnoses. Comorbidities included neurologic (29.9% vs 24.6%; P <.001); cardiovascular (51.2% vs 40%; P <.001); metabolic (51.5% vs 42%; P <.001); renal (33.3% vs 19.4%; P <.001); hepatic (6.5% vs 3.9%; P <.001); immunosuppressive (19.4% vs 16.8%; P <.001); and hematologic (5.8% vs 4.2%; P <.001) diagnoses.

Patients with only non-respiratory diagnoses were less likely to receive antiviral treatment compared to those with a respiratory diagnosis (81.4% vs 89.9%; P <.001).

Overall, the most common acute respiratory diagnoses were flu with other respiratory manifestations (56.1%) and pneumonia (36.3%). For non-respiratory patients, the most common diagnoses were sepsis (23.3%), acute kidney injury (20.2%), and acute cardiovascular events (12.1%).

Flu A was detected in 80% of patients with acute respiratory and non-respiratory diagnoses.

During flu season, the study investigators suggested that providers consider flu in their diagnosis for patients who arrive at the hospital with less frequently recognized manifestations and initiate early antiviral treatment.

The study, “Respiratory and Nonrespiratory Diagnoses Associated With Influenza in Hospitalized Adults,” was published online in JAMA Network Open.