Indicators of influenza activity: Trend and Dominant typeCornelia Adlhoch, ECDCAnnual Influenza Meeting, Stockholm 11 June 2015

Trend

Trend

described as weekly clinical morbidity rate vs. previous week:

• increasing: evidence that the level of respiratory disease activity is increasing compared to the previous week;

• stable: evidence that the level of respiratory disease activity is unchanged compared to the previous week;

• decreasing: evidence that the level of respiratory disease activity is decreasing compared to the previous week.

Trend – Discussion points

Consider to change to comparison in the level of the ILI/ARI incidence rate to the past two or three weeks and calculate automatically by the system?

What if:

• weeks are contradictious? -> new classification? e.g. fluctuating/shifting/changing/... or no display?

• changes are insignificant? -> threshold necessary?

• information is missing? -> no display?

Dominant Type

Dominant virus types season 2014/15, EU/EEA

Dominant: > 60%

Sentinel system

Dominant virus definition

“Dominant type is assessed based on data from sentinel and non-sentinel sources”

The prevailing virus type (or subtype) over the others with a threshold for dominance and co-dominance OR prevalent and co-prevalent.

Dominance: 60%

Co-dominance: 40% / 60%

Dominant virus - Discussion points

Challenges:

• Discrepant use of sentinel and non-sentinel data for reporting.

• Indicator provided does not match with the data reported.

Suggestion:

Automatic calculation on the reported sentinel data using thresholds:

Dominant virus: One virus type/subtype ≥60%

Co-circulation: Two virus types/subtypes >40% and <60% Examples: Reporting:

65% A(H1N1)pdm09, 35% B A(H1N1)pdm09

55% A(H1N1)pdm09, 40% A(H3N2) A(H1N1)pdm09 + A(H3N2)

40% A(H1N1)pdm09, 35% A(H3N2) and 25% B Influenza A

50% B, 40% A(H1N1)pdm09 Influenza A + B