Table 1. ICD-9-CM Codes for Influenza-like Illness (ILI) Diagnosis, comparing seasonal versus early period of pandemic H1N1 2009.
| ICD-9-CM Code 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 |
| Viral Infection NEC | 079.89 | 202 | 0.04 | 0.04 | 130 | 0.08 | 1.80 | 1.44–2.26 | 1.00E-07 |
| Viral Infection NOS | 079.99 | 5031 | 1.05 | 1.07 | 2467 | 1.44 | 1.38 | 1.31–1.45 | <1.00E-07 |
| Nasopharyngitis, acute | 460 | 12490 | 2.61 | 2.66 | 2606 | 1.52 | 0.58 | 0.55–0.60 | <1.00E-07 |
| Pharyngitis, acute | 462 | 35719 | 7.46 | 7.62 | 14758 | 8.63 | 1.17 | 1.15–1.19 | <1.00E-07 |
| Laryngitis, acute, without obstruction | 464.00 | 1426 | 0.3 | 0.30 | 565 | 0.33 | 1.11 | 1–1.22 | 0.03769 |
| Tracheitis, acute, without obstruction | 464.10 | 221 | 0.05 | 0.05 | 74 | 0.04 | 0.94 | 0.71–1.23 | 0.6273 |
| Laryngotracheitis, acute without obstruction | 464.20 | 20 | 0.004 | 0.004 | 8 | 0.005 | 1.12 | 0.45–2.67 | 0.7877 |
| Laryngopharyngitis, acute | 465.0 | 113 | 0.02 | 0.02 | 48 | 0.03 | 1.19 | 0.84–1.69 | 0.31543 |
| Infectious upper respiratory, multiple sites, acute NEC | 465.8 | 186 | 0.04 | 0.04 | 71 | 0.04 | 1.07 | 0.80–1.42 | 0.63681 |
| Infectious upper respiratory, multiple sites, acute NOS | 465.9 | 116520 | 24.35 | 24.85 | 34244 | 20.02 | 0.78 | 0.77–0.79 | <1.00E-07 |
| Bronchitis, acute | 466.0 | 66201 | 13.83 | 14.12 | 20716 | 12.11 | 0.86 | 0.84–0.87 | <1.00E-07 |
| Bronchiolitis due to RSV | 466.11 | 10 | 0.002 | 0.002 | 7 | 0.004 | 1.96 | 0.67–5.57 | 0.1646 |
| Bronchiolitis, acute, due to other infectious organism | 466.19 | 278 | 0.058 | 0.059 | 94 | 0.055 | 0.95 | 0.74–1.20 | 0.642 |
| Disease, upper respiratory NEC/NOS | 478.9 | 431 | 0.09 | 0.09 | 169 | 0.099 | 1.1 | 0.91–1.32 | 0.307 |
| Pneumonia due to adenovirus | 480.0 | 0 | 0 | 0.00 | 1 | 0.0006 | NA | NA | 0.943 |
| Pneumonia due to RSV | 480.1 | 1 | 0.0002 | 0.0002 | 2 | 0.001 | 5.6 | 0.4–155.7 | 0.113 |
| Pneumonia due to parainfluenza | 480.2 | 3 | 0.0006 | 0.0006 | 0 | 0.00 | 0 | 0–6.23 | 0.3 |
| Pneumonia due to virus NEC | 480.8 | 23 | 0.005 | 0.005 | 7 | 0.004 | 0.85 | 0.33–2.08 | 0.709 |
| Viral pneumonia unspecified | 480.9 | 76 | 0.016 | 0.016 | 29 | 0.017 | 1.07 | 0.68–1.67 | 0.764 |
| Pneumonia in other infectious disease NEC | 484.8 | 25 | 0.005 | 0.005 | 14 | 0.008 | 1.57 | 0.77–3.14 | 0.175 |
| Bronchopneumonia organism NOS | 485 | 461 | 0.096 | 0.098 | 127 | 0.074 | 0.77 | 0.63–0.94 | 0.0092 |
| Pneumonia, organism NOS | 486 | 58286 | 12.18 | 12.42 | 22121 | 12.94 | 1.07 | 1.05–1.09 | <1.00E-07 |
| Influenza with pneumonia | 487.0 | 63 | 0.013 | 0.013 | 38 | 0.022 | 1.69 | 1.11–2.57 | 0.00995 |
| Influenza with respiratory manifestation NEC | 487.1 | 7175 | 1.50 | 1.53 | 1762 | 1.03 | 0.68 | 0.65–0.72 | <1.00E-07 |
| Influenza with other manifestation NEC | 487.8 | 37 | 0.0077 | 0.0079 | 45 | 0.026 | 3.4 | 2.16–5.37 | <1.00E-07 |
| Bronchitis NOS | 490 | 58007 | 12.12 | 12.37 | 17584 | 10.28 | 0.83 | 0.82–0.85 | <1.00E-07 |
| Fever and other physiologic disturbances of temperature regulation | 780.60/780.6 | 15268 | 3.19 | 3.26 | 9213 | 5.39 | 1.73 | 1.68–1.77 | <1.00E-07 |
| Chills (without fever) | 780.64 | 1013 | 0.21 | 0.22 | 483 | 0.28 | 1.34 | 1.20–1.49 | 2.00E-07 |
| Hypothermia not assoc with low environmental temperature | 780.65 | 103 | 0.022 | 0.022 | 29 | 0.017 | 0.79 | 0.51–1.21 | 0.255 |
| Pain, throat | 784.1 | 2949 | 0.62 | 0.63 | 1523 | 0.89 | 1.45 | 1.36–1.54 | <1.00E-07 |
| Cough | 786.2 | 96206 | 20.1 | 20.51 | 42095 | 24.61 | 1.3 | 1.28–1.31 | <1.00E-07 |