Objective: To determine factors that might account for a significantly lower attack rate in a newly constructed nursing building during an epidemic of type A influenza.
Setting: A four-building, long-term care facility for veterans and their spouses, with an average daily census of 690.
Design: Prospective surveillance with retrospective analysis.
Participants: Symptomatic residents submitting to viral culture.
Measurements: Number of respiratory illnesses and influenza cultures in consenting symptomatic residents. Building characteristics.
Results: An influenza A (H3N2) outbreak was culture-confirmed in 68 nursing home residents. Influenza A was isolated in 3/184 (2%) residents in Building A, 31/196 (16%) in Building B, 18/194 (9%) in Building C, and 16/116 (14%) in Building D. Denominators are average daily census during the outbreak. Building A had significantly fewer culture-confirmed cases than the other buildings (P < .001). Fewer residents in Building A, 47% compared with 61% in Buildings B, C, and D, were participants in a formal study of influenza. Eight of 15 respiratory illnesses identified during the outbreak that were not cultured occurred in Building A. These factors could not account for the difference in attack rates. Building A has a unique ventilation system, more square feet of public space per resident, and does not contain office space that serves the entire four-building facility.
Conclusion: Our retrospective observation suggests that architectural design may influence the attack rate of influenza A in nursing homes.