A strict mask policy for hospital staff effectively prevents nosocomial influenza infections and mortality: monocentric data from five consecutive influenza seasons

Influenza infections acquired in hospital show increased mortality, especially in elderly patients with risk factors. Nevertheless, vaccination rates are low among both high-risk patients and healthcare workers (HCWs).To more effectively prevent influenza infections in the hospital during the influenza season, a strict mouth-nose protection (MNP) requirement was introduced for all staff throughout the shift on the affected wards as an intervention and its effect on nosocomial infection rates was studied.The present data were obtained in a retrospective, monocentric analysis over a period of four consecutive influenza seasons from 2015 to 2019. MNP for all staff during the whole shift as an intervention was introduced in 2017 and for the following seasons if at least three influenza patients were in the ward at the same time. Data from hospitalized influenza patients before and after intervention were compared with regard to nosocomial incidences and mortality.In the years with strict mandatory MNP (2017-2019), the nosocomial influenza incidence fell nearly 50% (odds ratio: 0.40; 95% confidence interval: 0.28-0.56; P < 0.001) accompanied by a significant reduction in nosocomial mortality by 85% (0.15; 0.02-0.70; P = 0.007). The infectious pressure indicated by influenza incidences and patient-days at risk were comparable before and after intervention, as was the low rate of vaccine uptake by nurses.Mandatory MNP for HCWs effectively protects patients from nosocomial influenza infections and mortality.