Table 3. Correlations between IMS indicators for ILI and RSV activity vs traditional influenza surveillance datasets maintained by the CDC.

	IMS-ILI indicator and:			IMS RSV indicator and CDC RSV activity
Outcome	CDC-ILI	CDC influenza viral activity	CDC RSV activity
Weekly incidence	0.97 (1)	0.93 (0)	0.33 (0)*	0.94 (0)
Peak week	0.99	0.97	0.21	0.97
Intensity	0.90	−0.10	0.43	0.77

Correlation between IMS-ILI and CDC RSV laboratory-confirmed viral activity can be considered as a control comparison testing the specificity of IMS-ILI for influenza surveillance. Analyses performed at the national scale, 2003–04 to 2009–10. Values indicate Pearson correlation coefficients; values in bold are significant (P<0.05).

*Correlation for this control comparison is significantly weaker than for the other comparisons (P≤ 0.05), indicating that the IMS-ILI indicator is specific of weekly influenza activity while the IMS RSV indicator is specific of weekly RSV activity.