Weekly influenza surveillance overview, 26 March - 1 April 2012, week 13/2012

The 2011–2012 influenza season started late and has been without any clear geographic progression. During week 13/2012, medium or low intensity was reported in 25 countries, with decreasing trends in 19 countries. Only Slovakia reported an increasing trend. During week 14/2012, medium or low intensity was reported in 26 countries, with decreasing trends reported by 20 countries, and no country reporting an increasing trend. Of those, 18 countries reported decreasing trends for two consecutive weeks, suggesting that their influenza seasons have peaked.

Virological surveillance for week 13/2012 shows that of 678 sentinel specimens tested, 244 (36.0%) were positive for influenza virus. The proportion of sentinel specimens testing positive for influenza virus has decreased over five consecutive weeks from a peak approaching 60%. Of the positive sentinel specimens 77.9% were type A and 22.1% type B.

For week 14/2012, of the 439 sentinel specimens tested, 132 (30.1%) were positive for influenza virus. The proportion of sentinel specimens testing positive for influenza virus has decreased over six consecutive weeks from a peak of 60% in week 8. Of the positive sentinel specimens 65.2% were type A and 34.8% type B. This is the highest proportion of B-type viruses in sentinel samples so far this season, as could be expected at this stage in the season.

Since week 40/2011, a total of 1 685 SARI cases, including 97 fatalities, have been reported by seven countries. Of these cases, most were influenza-related.

No resistance to neuraminidase inhibitors (oseltamivir and zanamivir) has been reported so far this season.