Influenza outbreaks in Ontario hospitals, 2012-2016

Area of Science:

• Infectious Diseases
• Epidemiology
• Public Health

Background:

• Hospital-acquired influenza outbreaks present significant risks to vulnerable patients, including increased morbidity and mortality.
• Limited data exists on the characteristics and impact of influenza outbreaks within healthcare settings.

Purpose of the Study:

• To analyze surveillance data for hospital influenza outbreaks in Ontario from 2012-13 to 2015-16.
• To compare the frequency, duration, and severity of outbreaks during seasons dominated by influenza A H3N2 versus H1N1 strains.

Main Methods:

• Retrospective analysis of laboratory-confirmed hospital influenza outbreaks between September 2012 and August 2016.
• Evaluation of outbreak indicators: duration, case attack rate, pneumonia rate, and fatality rate.
• Comparison of outbreak characteristics between H3N2-dominant and H1N1-dominant influenza seasons.

Main Results:

• A total of 256 outbreaks affected 1,586 patients, resulting in 91 pneumonia cases and 40 deaths over four years.
• The 2014-15 season (H3N2-dominant) reported the highest number of outbreaks (117), cases (753), pneumonia cases (46), and fatalities (18).
• No statistically significant differences in outbreak duration or severity were found between H3N2 and H1N1 seasons, though H3N2 seasons had more influenza A than B outbreaks.

Conclusions:

• H3N2-dominant influenza seasons are associated with a higher incidence of hospital outbreaks, contributing to influenza-related morbidity and mortality.
• Despite variations in outbreak frequency, the duration and severity of influenza A outbreaks do not significantly differ between H3N2 and H1N1 dominant seasons.