DURATION OF ANTIVIRAL PROPHYLAXIS DURING NURSING-HOME OUTBREAKS OF INFLUENZA-A - A COMPARISON OF 2 PROTOCOLS

Background: We performed a randomized trial of 2 protocols guiding the duration of antiviral chemoprophylaxis during outbreaks of influenza A in a rural, 700-bed nursing home for veterans and their spouses with 14 nursing units in 4 buildings. Methods: Half of all residents volun teered to participate. Nursing units were randomized, and the effectiv eness of short-term (minimum, 14 days and 7 days without the onset of a case in the building) vs longterm (minimum, 21 days and 7 days witho ut the onset of a case in the Lt-building facility) prophylaxis was co mpared using amantadine hydrochloride in the influenza seasons of 1991 -1992 and 1993-1994 and rimantadine hydrochloride in the influenza sea son of 1994-1995. A ''case'' is defined as an incident of a respirator y tract illness and the isolation of an influenza virus organism. We c ompared the number of cases after the discontinuation of short- vs.lon g-term chemoprophylaxis. Prospective surveillance identified residents with new respiratory tract symptoms, and specimens for viral cultures were obtained even in the absence of temperature elevation. Results: We documented influenza A virus activity during 3 seasons (32,68, and 12 patients, respectively). During the 1991-1992, 1993-1994, and 1994- 1995 influenza seasons, the patients on 11 floors were assigned to rec eive short-term chemoprophylaxis and those on 10 floors were assigned to long-term chemoprophylaxis. Only in 1993-1994 did chemoprophylaxis extend beyond 14 or 21 days when new cases continued beyond 14 days. A mantadine-resistant strains were circulating at that time. None of the participants in the prospective, controlled study had influenza devel op after the termination of short- or long-term chemoprophylaxis. Conc lusion: Antiviral chemoprophylaxis can be administered for the longer duration of 14 days or, in the absence of new culture-confirmed illnes s in the nursing building, for 7 days.