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closeFurther analysis appropriate
Posted by tmerritt on 29 Jan 2013 at 10:49 GMT
This paper by Booy et al is a welcome addition to a very limited literature available to guide the prophylactic use of antivirals in confirmed institutional influenza outbreaks. Given the limited evidence base, it is particularly important that any qualifications to the study conclusions are carefully considered.
The use of oseltamivir for both treatment and prophylaxis (T&P) was reported to significantly reduce outbreak duration and attack rate in comparison to use of oseltamivir for treatment only (T), with the authors concluding that the trial provided “some support for a policy of treatment and prophylaxis with oseltamivir in controlling influenza outbreaks in ACFs”. However, differences in deaths, hospitalisations and pneumonia were not significant. Popular medical media have lauded the work as a “landmark study” and reported that the “results provide good evidence to support an active policy of treating and preventing influenza promptly, once an outbreak is declared” (1).
Unfortunately the underpowered nature of this study, with just three facilities randomised to T and six to T&P, meant that a single outbreak could have a substantial impact on the results.
Indeed, inclusion of a particular T outbreak (Facility B) seriously limits the interpretation of this study. Data from the paper and subsequently provided by the authors, indicated that the time from first influenza-like illness (ILI) case to intervention commencing was approximately 20 days, at which time there were already 22 ILI cases in the facility. Treatment was provided to fewer than half the ILI cases and the intervention was subsequently changed to T&P after about 10 days. In contrast, the mean time from first ILI case to outbreak intervention was 12.7 days in T facilities overall and 5.0 days in T&P facilities.
The unusual nature of the outbreak in Facility B and its management dictate that the analysis is repeated excluding this facility. It appears that the reported difference in outbreak duration would be non-significant if facility B was excluded, providing important qualification to the study conclusions. Differences in hospitalisations and deaths would be further reduced and remain non-significant.
Tony Merritt
Public Health Physician
Hunter New England Population Health
David Durrheim
Director, Health Protection
Hunter New England Population Health
Reference
(1) A new approach to deadly influenza outbreaks in nursing homes. 18 October 2012. [Cited 19 January 2013]. Available from URL http://www.healthcanal.co...