Information has now been received confirming that an earlier outbreak, which occurred during the first week of September in a boys’ secondary school in County Kildare (near to Dublin city, and about 30 kilometres from the school in reference 1), was also caused by influenza A H3N2. The first patient to be admitted to hospital arrived in the early hours of 3 September. Thirteen more boys were admitted to hospital during the following 24 hours, all of whom had what appeared to be a severe influenza-like illness. The boys were confined to one particular ward. A total of 23 boys were admitted to hospital during the outbreak, nine of whom were referred by their general practitioners. Those admitted were prostrate, and some were given intravenous fluids. Nearly all had high fevers (temperatures of 103-104 degrees fahrenheit were recorded), and had severe aches and pains. A total of 160 students and four teachers were reported to be ill. The attack rate in the sixth class (16-18 year old boys) where the illness was first identified was 45%. To date, the earliest date for onset of symptoms as identified in a questionnaire given to students and staff is 28 August. The predominant symptoms were fever, headache, sore throat and myalgia. The school, which has 800 day pupils and no boarders, was closed on 4 September. Television and radio announcements were made by a specialist in public health from the Eastern Regional Health Authority advising the public to stay home if ill, to wash their hands, and to consult their local general practitioner if worried.

Throat swabs, blood for serology and stools were sent for bacteriological and viral culture. Influenza A (H3N2) was detected by polymerase chain reaction (PCR) by the Virus Reference Laboratory in 12 out of 15 cases. Serological investigation later confirmed rising titres in 5 cases. Investigations are continuing to further characterise the virus strain.

A retrospective cohort study of this outbreak will be reported at a later date.

This latest information confirms early influenza A activity in Ireland this year. Healthcare professionals in hospitals and in the community should be aware of this early activity and consider influenza as a diagnosis in any outbreaks of respiratory illness that are reported. This emphasises the importance of vaccinating vulnerable groups as early as possible this season.

The European Influenza Surveillance Scheme (EISS) published the EISS Weekly Electronic Bulletin throughout the influenza season, and the latest bulletin can be accessed at http://www.eiss.org.