Update by Dr J Gallagher, Employment Health Advisors (EHA):
Influenza activity in Ireland is slowly increasing; with an increase in influenza positivity and confirmed influenza outbreaks reported during week 4 2015.
The sentinel GP influenza-like illness (ILI) consultation rate was 31.3 per 100,000 population in week 4 2015, remaining low, and stable compared to the updated rate of 30.4 per 100,000 population during week 3 2015. ILI rates remained above the Irish baseline threshold (21.0 per 100,000 population). ILI rates increased in the 0-4 and 5-14 year age groups during week 4 2015. The proportion of influenza–related calls to GP Out-of-Hours services increased slightly during week 4 2015.
Influenza positivity increased during week 4 2015, with 81 (23.5%) influenza positive specimens reported from the NVRL: 73 A(H3), 1 A(H1)pdm09, 4 A (not subtyped) and 3 B. Influenza A(H3) is the predominant circulating influenza virus this season. Respiratory syncytial virus (RSV) positivity has decreased significantly in recent weeks. Respiratory admissions: The latest complete data on respiratory admissions reported from a network of sentinel hospitals were elevated. 18 confirmed influenza hospitalised cases were notified to HPSC during the week ending January 25th 2015: 15 associated with influenza A(H3), one with influenza A(H1)pdm09 and two with influenza A (not subtyped). Six influenza A-associated deaths have been reported to HPSC this season, five associated with influenza A(H3) and one with influenza A (not subtyped). Eight acute respiratory outbreaks were reported to HPSC during the week ending January 25th 2015: six associated with influenza A(H3), one with RSV and one with no pathogen identified.
The majority of confirmed influenza outbreaks this season have been associated with influenza A(H3) in community hospitals/residential care facilities for the elderly. Globally, influenza activity was high in the northern hemisphere with influenza A(H3N2) viruses predominating this season. Antigenic characterisation of most recent A(H3N2) viruses this season indicated differences from the A(H3N2) virus used in the influenza vaccines for the northern hemisphere 2014/2015. As a consequence of the mismatch between vaccine and circulating strains, reduced vaccine effectiveness is expected. Vaccination of the elderly and other risk groups is still recommended, as the A(H3N2) component is expected to reduce the likelihood of severe outcomes due to cross-protection, and both the A(H1N1)pdm09 and influenza B components are expected to be effective.