Table 2. ICD-9-CM Codes for Influenza-like Illness (ILI) Subgroups, comparing seasonal versus early period of pandemic H1N1 2009.

ICD-9-CM Grouping Description	ICD-9-CM Code	Total for 9/28/08-4/25/09	Percent Total/Individual	Percent Total/ILI	Total for 4/26/09-7/31/09	Percent Total/Individual	Crude OR	CI	P Value
Bronchitis	466.0, 466.11, 466.19, 490.	124496	26.02	26.55	38401	22.45	0.82	0.81–0.83	<1.00E-07
Cough	786.2	96206	20.10	20.51	42095	24.61	1.3	1.28–1.31	<1.00E-07
Disease of Upper Respiratory Tract	478.9	431	0.09	0.092	169	0.099	1.1	0.91–1.32	0.3066805
Fever	780.6, 780.60, 780.64, 780.65	16384	3.42	3.49	9725	5.686	1.17	1.66–1.75	<1.00E-07
Influenza	487.0, 487.1, 487.8	7275	1.52	1.55	1845	1.08	0.71	0.67–0.74	<1.00E-07
Pneumonia	480.0, 480.1, 480.2, 480.8, 480.9, 484.8, 485, 486	58875	12.30	12.55	22301	13.04	1.07	1.05–1.09	<1.00E-07
Sore Throat	784.1	2949	0.62	0.63	1523	0.89	1.45	1.36–1.54	<1.00E-07
URI	460., 462., 464.00, 464.10, 464.20, 465.0, 465.8, 465.9	166695	34.83	35.55	52374	30.62	0.83	0.82–0.84	<1.00E-07
Viral Infection	079.89, 079.99	5233	1.09	1.11	2597	1.52	1.39	1.33–1.46	<1.00E-07