Objective
To investigate the difference of disease severity between influenza A and B among hospitalized adults using a novel ordinal scale and existing clinical outcome endpoints.
Methods
A prospective, observational study was conducted over 2016-2018 influenza seasons in a central hospital. The primary outcome was the rate of clinical improvement defined as the decline of two categories from admission on a seven-category ordinal scale which ranges from 1 (discharged with normal activity) to 7 (death), or hospital discharge up to 28 day.
Results
Totally, 574 eligible patients were enrolled, including 369 (64.3%) influenza A cases and 205 (35.7%) influenza B cases. The proportion of patients with worse ordinal scale at admission was higher in influenza A than influenza B (P = 0.0005). Clinical improvement up to 28 days occurred in 82.4 % of the patients with influenza A and in 90.7 % of the patients with influenza B (P=0.0067). The COX model indicated influenza B patients had a higher clinical improvement probability than influenza A cases (adjusted Hazard Ratio, 1.266; 95% CI, 1.019–1.573; P=0.0335). A similar pattern was observed in weaning oxygen supplement (adjusted HR, 1.285; 95% CI, 1.030–1.603; P = 0.0261). In-hospital mortality for influenza A was marginally higher than influenza B (11.4% vs 6.8%, P=0.0782).
Conclusions
Our findings indicated that hospitalized patients with influenza A were more ill and had delayed clinical improvement compared to those with influenza B virus infection.