| Feature | HME | HGA |
| Etiologic agent | E. chaffeensis | A. phagocytophilum |
| Percent with tick exposure | 80 to 90 | 45 to 85 |
| Percent with tick bite | 68 | 67 |
| Vectors | Amblyomma americanum | Ixodes scapularis |
| Ixodes pacificus | ||
| Suspected animal reserve | Deer | White-footed mouse |
| Median age of patient | 44 | 67 |
