Experience with oseltamivir in the control of a nursing home influenza B outbreak.

Oseltamivir prophylaxis was very effective in protecting nursing home residents from ILI and in halting this outbreak of influenza B. A portion of the total ILI cases may have been due to influenza A, as this strain was isolated in one resident. The 10% attack rate in this facility, controlled with oseltamivir, compares favourably with another influenza B outbreak in a similar facility in the same region, over the same time frame (ILI onset 27 December to 17 January). Oseltamivir prophylaxis was not used to manage this second outbreak of laboratory-confirmed influenza B. Of the 236 residents, 45 developed ILI for an overall attack rate of 19%, nearly double the rate in the oseltamivir-controlled setting (10%). While oseltamivir was effective in controlling influenza B in this outbreak, further experience and evaluation is required before it can be routinely recommended for prophylaxis of influenza in nursing home outbreaks. Although earlier attempts by others using oseltamivir in the control of influenza A outbreaks have also met with success, it is not yet licensed for this purpose. Compared to amantadine, oseltamivir has a relatively high cost for the control of influenza A outbreaks and this may continue to limit its wider acceptance. The cost-effectiveness of oseltamivir in the control of influenza B outbreaks needs to be specifically addressed given the typically milder nature of influenza B strains. However, such a distinction is not clinically reliable and elderly residents of long-term care facilities remain vulnerable to serious complications associated with influenza infection in general. An alternate agent for influenza chemoprophylaxis that is effective against both influenza A and B, is easily administered and has few side effects, could greatly enhance current prevention and control measures and warrants serious assessment. The spread of this outbreak from the geographically separate ward to other areas of the facility in which residents had not received prophylaxis, underscores the likely role of staff as a vehicle for transmission during facility outbreaks. While accurate staff ILI rates could not be determined, their immunization rates were low, and many staff were ill during the outbreak. Isolation of residents with ILI and prophylaxis of non-ill residents on the initial outbreak wards was insufficient to prevent the spread of the outbreak, although it was subsequently halted once prophylaxis was extended to all residents. In view of the uncertainty over this medication's widespread use, in the absence of licensure or previous studies demonstrating its effectiveness in the prophylaxis and control of influenza B outbreaks, initiation of oseltamivir prophylaxis was staggered by ward. In a declared influenza A outbreak, the protocol in a long term care facility is to initiate amantadine prophylaxis on all residents, rather than ward-by-ward. While anti-viral prophylaxis may be an effective secondary control measure in the management of influenza outbreaks, optimal primary prevention would be more effective. This would require increased vaccine coverage of residents and particularly of staff, who play an important role in the importation and transmission of influenza within these facilities.