Comparison of the Demographics, Clinical Presentations, Seasonality, and Outcome between Adult Patients with Influenza A and B in Two Seasons (2014-2015 and 2015-2016) with Emphasis on H1N1 Infection Outcome

Abstract

Background: Studies comparing Influenza A and B in our community are extremely limited. Methods: Adult patients (n=1708) with ILI who visited the outpatient clinics or emergency department with FIA-positive nasal swab in two seasons were included in the analysis. Data on demographics, clinical presentation, comorbidities, and prolonged illness (revisit after 48 hours with same presentation and no admission), hospital admissions, death, and LOS were collected. Data on patients tested for H1N1 (309) by Cepheid Xpert Flu Assay (H1N1 positive, 143 [46%]; H1N1 negative, 166 [54%]) were also collected. Results: Prolonged illness was more frequent in patients with influenza B than those with influenza A (15.21% and 10.18%, respectively; P=0.002). There was no significant difference in frequency of total admissions, medical unit or intensive care unit admissions, LOS, and death between patients with influenza A and B. Total admissions were more frequent in H1N1-positive patients than H1N1-negative patients (23.1% and 13.3%, respectively; P=0.024). Prolonged illness was more frequent in H1N1-positive patients (23.1%) than H1N1-negative patients (4.8%) (P < 0.001). There was no statistically significant difference in admission to the medical unit or ICU, death, and LOS between H1N1-positive and H1N1-negative patients. The peak months of influenza A were December in the first season and October in the second season. April was the peak month of influenza B in both seasons. There was no statistically significant difference in the outcome of pregnant patients with influenza (either A or B) compared to non-pregnant women with influenza within the same childbearing age (maternal outcome was not studied). Conclusion: Prolonged illness was more frequent in flu B than in flu A patients. Patients with positive H1N1 had more frequent prolonged illness, and total hospital admissions than those with H1N1-negative patients. There was a different peak month(s) of patients with flu A compared to flu B.