Table 3. ICD-9-CM codes that significantly changed since the start of pandemic H1N1 2009.

ICD-9-CM Description	ICD-9-CM Code	Change during pandemic H1N1 2009	% Before H1N1	% During H1N1	p-value	OR	CI
Acute nasopharyngitis	460	Decreased	2.61	1.52	<1.00E-07	0.58	0.55–0.60
Acute upper respiratory infection (URI) NOS	465.9	Decreased	24.35	20.02	<1.00E-07	0.78	0.77–0.79
Acute bronchitis	466.0	Decreased	13.83	12.11	<1.00E-07	0.86	0.84–0.87
Bronchopneumonia organism NOS	485	Decreased	0.096	0.074	<0.01	0.77	0.63–0.94
Influenza with respiratory manifestation NEC	487.1	Decreased	1.50	1.03	<1.00E-07	0.68	0.65–0.72
Bronchitis NOS	490	Decreased	12.12	10.28	<1.00E-07	0.83	0.82–0.85
Viral infection NEC	079.89	Increased	0.042	0.76	<1.00E-06	1.8	1.44–2.26
Viral infection NOS	079.99	Increased	1.051	1.442	<1.00E-07	1.38	1.31–1.45
Acute pharyngitis	462	Increased	7.464	8.629	<1.00E-07	1.17	1.15–1.19
Acute laryngitis without obstruction	464.00	Increased	0.298	0.330	0.038	1.11	1–1.22
Pneumonia, organism NOS	486	Increased	12.18	12.94	<1.00E-07	1.07	1.05–1.09
Influenza with pneumonia	487.0	Increased	0.013	0.022	<0.01	1.69	1.11–2.57
Influenza with other manifestation	487.8	Increased	0.0077	0.026	<1.00E-07	3.4	2.16–5.37
Fever	780.60/780.6	Increased	3.19	5.39	<1.00E-07	1.73	1.68–1.77
Chills without fever	780.64	Increased	0.212	0.282	<2.00E-07	1.34	1.20–1.49
Pain, throat	784.1	Increased	0.616	0.890	<1.00E-07	1.45	1.36–1.54
Cough	786.2	Increased	20.10	24.61	<1.00E-07	1.3	1.28–1.31