Diana Mahoney is with the New England bureau of Elsevier Global Medical News.
Nursing homes turning to the antiviral drug oseltamivir to prevent seasonal influenza can use the drug either before or after residents' exposure to infection, according to a computer model of outbreaks in a small facility. Either dispensing oseltamivir continuously during 8 weeks of flu season or giving it for only 8 days after a nursing home's first influenza infection was confirmed substantially reduced cases in the model.
The findings support previous observational and experimental studies, Carline van den Dool, PhD, of the University Medical Center, Utrecht, the Netherlands, and her colleagues wrote in the Emerging Infectious Disease (2009; [doi:10.3201/eid1510.081129]). Continuous prophylaxis did prevent more seasonal influenza infections than postexposure prophylaxis did, but the latter strategy required only a third as many oseltamivir doses per avoided infection and so could be the preferred approach, the researchers wrote.
The investigators simulated influenza outbreaks during an 80-day period in a typical 30-bed, 15-room nursing home in the Netherlands. The model accounted for contact between residents and 30 full-time employees, the likelihood of risk-elevating medical conditions, and a typical flu-vaccination rate in such a facility. The investigators compared the continuous and postexposure prophylaxis strategies with each other and a control situation in which no prophylactic drug was used.
In the simulations, the infection-attack rate among patients—defined as total infections during the 80 days divided by the number of residents in the nursing home—was 0.19 in the control scenario, 0.13 with postexposure prophylaxis, and 0.05 with continuous-prophylaxis setting, representing relative risks of 0.67 and 0.23, respectively, with the two prophylaxis strategies. Although the number of infections prevented was higher for continuous prophylaxis, that strategy took 323 doses of the drug to prevent one influenza infection vs. 118 doses in the postexposure strategy.
Extending either prophylactic strategy to health care workers did not offer significant additional protection to residents, the authors noted. Additionally, as community resistance to the oseltamivir increased, the efficacy of both strategies decreased and the doses needed to prevent infection rose rapidly, particularly with the continuous-prophylaxis scenario, suggesting that “increasing resistance should be included in the decision-making process for prevention of influenza in health care settings,” the researchers wrote. “Use of other antiviral agents that are not as associated with resistance should be considered as an alternative prevention strategy.”
The study results are limited by the fact that the model did not distinguish between different subtypes of influenza circulating in the community and it did not account for de novo resistance in persons receiving prophylaxis, according to the authors. Additionally, the model relied on estimates of the efficacy of oseltamivir prophylaxis from household studies rather than data specific to elderly populations. “More accurate assessment of efficacy and comparison of preventive measures in nursing homes will require new estimates from studies in senior populations,” the team wrote.
“This is a mathematical model, not a randomized control trial and, like all mathematical models, it makes a lot of assumptions that may not apply to long-term care populations,” said Dr. David Nace, director of the long-term care and flu programs at the University of Pittsburgh Institute on Aging. “As clinicians, we are always asking ourselves if prophylaxis is worth it, and this model suggests the answer is yes, even in the presence of resistance, where there is still some benefit depending on the level of resistance.”
Dr. Nace said that the study's take-home message is that “this prophylaxis strategy should be reserved for people at high risk for complications—those who are ill, frail, or hospitalized, for example—not all individuals and not even all health care workers. With respect to prevention in the general population, which includes health care workers, vaccination rather than antiviral prophylaxis gives far more bang for the buck.”
The study was funded by the Netherlands Health Care Organization, and the authors receive financial support from a Netherlands research organization.
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