Table 1.
ICD-9 codes used to identify mild and severe cases of influenza-like illness (ILI)
| 79·89 | Viral infection, NEC | 480 | Viral pneumonia |
| 79·99 | Viral infection, NOS | 480·8 | Pneumonia due to virus NEC |
| 460 | Nasopharyngitis, acute | 480·9 | Viral pneumonia unspecified |
| 461 | Sinusitis, acute | 481 | Pneumococcal pneumonia |
| 462 | Pharyngitis, acute | 482 | Other bacterial pneumonia |
| 463 | Tonsillitis, acute | 482·2 | Pneumonia due to Haemophilus influenzae |
| 464 | Laryngitis and tracheitis | 482·3 | Pneumonia due to Streptococcus |
| 464·01 | Laryngitis, acute, with obstruction | 482·4 | Staphylococcus pneumonia NOS |
| 464·1 | Tracheitis, acute, without obstruction | 482·41 | MSSA pneumonia |
| 464·11 | Tracheitis, acute, with obstruction | 482·49 | Other staphylococcus pneumonia |
| 464·2 | Laryngotracheitis, acute, without obstruction | 482·9 | Bacterial pneumonia unspecified |
| 464·21 | Laryngotracheitis, acute, with obstruction | 483 | Pneumonia due to other specified organism |
| 465 | Acute upper respiratory infections of multiple or unspecified sites | 484·8 | Pneumonia in other infectious disease |
| 464.2 | Laryngotracheitis, acute | 485 | Bronchopneumonia, organism NOS |
| 465·8 | Infectious upper respiratory, multiple sites, acute NEC | 486 | Pneumonia, organism NOS |
| 465·9 | Infectious upper respiratory, multiple sites, acute NOS | 487 | Influenza |
| 466 | Acute bronchitis and bronchiolitis | 487.0 | Influenza with pneumonia |
| 466.0 | Bronchitis, acute | 487·1 | Influenza with respiratory manifestation NEC |
| 466·1 | Bronchiolitis, acute | 487·8 | Influenza with manifestation NEC |
| 466·19 | Bronchiolitis, acute, due to other infectious organism | 784·1 | Pain, throat |
| 478·9 | Disease, upper respiratory NEC/NOS | 786·2 | Cough |
NOS, not otherwise specified; NEC, not elsewhere classified.
Cases had at least one of the respiratory codes listed, and a measured fever of at least 100F, an ICD-9 code of 780·6 (fever), or no measured temperature or ICD-9 code.