Antiviral prophylaxis is effective in reducing influenza outbreak severity in residential care

Abstract

Background: Influenza outbreaks in aged care facilities (ACFs) can lead to hospitalisations and deaths. Influenza can spread rapidly through ACFs if precautionary measures are not taken. Along with the influenza vaccination and precautionary hygiene measures, oseltamivir may be effective in reducing the attack rate of influenza. Methods and materials: Administrative data with enhanced surveillance of influenza outbreaks was used to investigate the effectiveness of oseltamivir prophylaxis use during influenza outbreaks in ACF located within South Western Sydney Local Health District from 1st January 2015 to December 31st 2018. The key outcome variable was the rate of seroconversion after receiving oseltamivir. Subgroups and various predictors of oseltamivir seroconversion were investigated including presence of a dementia ward, high care ward, strain of influenza, vaccination rates (staff and patients) and days to Public Health Unit (PHU) notification. Results: The cohort consisted of 86 ACF outbreaks involving 10,064 patients. Oseltamivir prevented 90% of influenza cases during influenza outbreaks. (0.1RR (95%CI: 0.0804–0.1248; p < 0.0001)). ACFs with dementia wards had a 44% (0.56RR (95%CI: 0.34–0.93); p < 0.05) lower oseltamivir seroconversion rate. ACFs with high level care had an 86% (0.13RR (95%CI: 0.05–0.38); p < 0.05) lower oseltamivir seroconversion rate. For each day delay in the ACF notifying the PHU of the influenza outbreak there was a 4% increase in the rate of deaths and 4% increase in hospitalisations among residents. For each day delay in notifying the PHU the duration of the outbreak was extended by 0.42 days. ACFs with only high care wards had 29% less clinical cases. The seroconversion rate was 87% lower in the high care ACFs indicating oseltamivir was more effective in the high care setting. Despite this, the rates of oseltamivir prescription was the same in high care only ACFs vs. other ACFs. There were 34% less clinical cases and 66% less hospitalisations in wards with influenza B compared with influenza A. Conclusion: Oseltamivir prophylaxis is highly effective in preventing new cases of influenza during outbreaks in ACFs, especially in facilities with dementia or high care wards. Mandatory reporting of influenza outbreaks in ACFs to PHUs will further assist in reducing hospitalisation, mortality and duration of outbreak.