Outbreak of influenza in an overseas student travel group--Taiwan 2008

Influenza is a frequent cause of acute respiratory illness (ARI). In July 2008, we conducted a retrospective cohort study to investigate an influenza outbreak occurring in an overland travel group of overseas students. ARI was defined as the presence of any respiratory symptom such as cough, rhinorrhoea, sore throat or stuffy nose. Influenza-like illness (ILI) was defined as ARI plus fever > or =38 degrees C. Throat swabs were taken from symptomatic participants and a real-time polymerase chain reaction (RT-PCR) was performed. One hundred and seventy participants were interviewed. Forty-four (26%) had an ARI and 22 (13%) had an ILI. Of the 33 specimens collected, 18 (54%) were positive for influenza A/H3N2. Taiwanese group leaders had increased risk of acquiring both ARI and ILI (ARI relative risk (RR) 2.2, 95% confidence interval (CI) 1.3-3.7 and ILI RR 2.8, 95% CI 1.2-6.3). Fifteen participants were vaccinated. The vaccine effectiveness was 52% for ILI (p = 0.70). The outbreak stopped after cohorting and the use of surgical masks. Vaccination appeared to be effective in preventing infection.