Is there a clinical difference between influenza A and B virus infections in hospitalized patients?

The clinical presentation, complications and mortality in molecularly confirmed influenza A and B infections were analyzed.

This retrospective observational single-centre study included all influenza positive patients older than 18 years who were hospitalized and treated at the flu isolation ward during 2017/2018. The diagnosis was based on point-of-care tests with the Alere^TM.

Of the 396 patients tested positive for influenza, 24.2% had influenza A and 75.8% influenza B. Influenza A patients were younger (median age 67.5 years vs. 77 years, p < 0.001), were more often smokers (27.7% vs. 16.8%, p = 0.021), had chronic pulmonary diseases more frequently (39.6% vs. 26.3%, p = 0.013), presented with a higher body temperature (38.6 °C vs. 38.3 °C, p = 0.004), leucocyte count (8 G/L vs. 6.8 G/L, p = 0.002), C‑reactive protein (CRP) level (41 mg/l vs. 23 mg/l, p < 0.001) and had dyspnea more often (41.7% vs. 28%, p = 0.012). Influenza B patients had an underlying chronic kidney disease in 37% vs. 18.8% (p < 0.001) and presented with vomiting on admission more frequently (21.7% vs. 11.5%, p = 0.027). Influenza A patients were admitted for 8 days vs. 7 days (p = 0.023). There were no differences in the rate of complications; however, 22 (5.6%) patients died during the hospital stay. The in-hospital mortality was higher in influenza A patients (8.3% vs 4.7%, p = 0.172).

Some differences were found between influenza A and B virus infections but symptoms were overlapping, which necessitates polymerase chain reaction point-of-care testing for accurate diagnosis. Influenza A was a more severe disease than influenza B during the period 2017/2018.