Weekly influenza surveillance overview, 23-29 January 2012 - Week 4

• During week 04/2012, while increased geographic spread was reported by 23 of 27 countries and increasing trends by 12 countries, the epidemic threshold was exceeded significantly in only four countries (Bulgaria, Iceland, Italy and Spain) and was just above threshold in Romania and Sweden.• Of 469 sentinel specimens testing positive for influenza, 95.7% were type A and 4.3% were type B. Of 650 influenza A viruses subtyped, including some from non sentinel sources, 96.6% were A(H3) and 3.4% were A(H1)pdm09. In the limited number of specimens that were tested for antiviral resistance, no antiviral resistance to the neuraminidase inhibitors (oseltamivir and zanamivir) was found.  • During week 04/2012, 38 SARI cases were reported to TESSy by six countries and 12 of these were influenza-related. Cumulatively this season, there have been 333 SARI cases. Where typing and subtyping had been performed, 16% were associated with A(H1)pdm09, 75% with A(H3) and 9% with type B. • Influenza activity was widespread in four countries and present or increasing in the rest of Europe. The subtype A(H3N2) is dominating the season to date but A(H1) and B viruses are also present.