We studied the effectiveness of oseltamivir during an outbreak of influenza A among previously vaccinated patients and staff in a long-term care facility. Seven of 14 staff members and 14 of 41 residents developed either influenza-like illness (ILI) or other respiratory symptoms during a 14-day period from late January to 8 February 2004. On 9 February, therapeutic oseltamivir (75 mg twice daily for five days) was administered to one staff member and seven residents who had developed ILI within the previous 48 h (treatment group). Prophylactic oseltamivir (75 mg once daily for seven days) was administered to 12 staff members and 30 residents who were asymptomatic or whose respiratory symptoms did not meet the diagnosis of ILI (prophylaxis group). The remaining four residents and one staff member had had ILI for more than two days (with subsiding symptoms) and did not receive oseltamivir ('no-oseltamivir' group). None of the 42 subjects in the prophylaxis group developed ILI. Presence of influenza A virus was demonstrated in 24 subjects: seven out of eight in the treatment group, 12 of 42 in the prophylaxis group and all five in the no-oseltamivir group. For confirmation of diagnosis, real-time reverse transcription-polymerase chain reaction was more sensitive than antigen detection and virus isolation. In-time therapeutic and prophylactic oseltamivir successfully interrupted an outbreak of influenza A in a long-term care facility.
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