Epidemiological characteristics of patients hospitalized with severe complicated influenza in Taiwan from 2010 to 2020: a retrospective study.

Influenza epidemics and pandemics are causes of morbidity and mortality. We explored the epidemiological differences and trends of domestic and imported severe complicated influenza cases in Taiwan from 2010 to 2020. To reinforce the efficiency of surveillance, the Taiwan Centers for Disease Control (TCDC) has established a surveillance system, called the Taiwan National Notifiable Disease Statistics System (TNNDSS). We created a trends study from the TNNDSS. A total of 14,844 domestic and 63 imported severe complicated influenza cases were reported. The number of reported cases and influenza positivity rate were the lowest in 2020. The incidence of severe complicated influenza was highest in 2019, ranging from 19 to 99 per 1,000,000 individuals from 2010 to 2020. In total, 1672 deaths were reported (case fatality rate, 11.2%). Most cases were in men (57.3%), were in those aged > 60 years (55.9%), occurred during winter (46.4%), and were in those residing in Northern Taiwan (46.9%). Comparing the gender, age, season and place of residence of the cases each year is statistically significant (p = 0.002, < 0.001, < 0.001, < 0.001, respectively). Furyhermore, comparing the total number of cases in the gender from 2010 to 2020, there are significant differences in the age groups (p < 0.001). In addition, comparing the total number of cases in each age group from 2010 to 2020, there are significant differences in the season and residency (p < 0.001, < 0.001, respectively). Influenza A virus subtype H1N1 was the dominant virus strain, and China was the most common country of origin for the imported cases.