Syndromic surveillance for influenza in two hospital emergency departments. Relationships between ICD-10 codes and notified cases, before and during a pandemic

Table 3 Correlation coefficients calculated between ICD-10 coded cases and NIDS cases, with and without lag periods: All Victorian data, excluding the 2009 influenza season

ICD-10 Code	Description	No lag*	1 week lag*	2 week lag*	3 week lag*
J11	Influenza virus not identified	0.433	0.417	0.456	0.404
J06	Acute upper respiratory infection multiple and unspecified sites	0.433	0.451	0.452	0.429
J22	Unspecified acute lower respiratory infection	0.424	0.417	0.435	0.367
B34	Viral infection, unspecified site	0.356	0.401	0.364	0.332
J18	Pneumonia organism unspecified	0.301	0.308	0.308	0.324

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