Table 2.
Number of Case and Control Patients, by History of Tick Exposure and Antibodies to Rickettsia rickettsii and Ehrlichia chaffeensis
| Characteristic | Case patients, n (%) | Control patients, n (%) | OR | LCL | UCL |
|---|---|---|---|---|---|
|
| |||||
| Tick exposure | |||||
| Found a tick on body in past year (or year before symptom onset) | 72 (88) | 90 (47) | 11.20 | 4.97 | 25.15 |
| Not found a tick on body in past year (or year before symptom onset) | 7 (9) | 98 (51) | Ref | — | — |
| Unsure about finding a tick on body in past year | 3 (4) | 3 (2) | — | — | — |
| Number of times ticks were found in past year | |||||
| 10 or more | 28 (39) | 15(17) | 4.20 | 1.91 | 9.24 |
| 7–9 | 3 (4) | 2 (2) | 3.11 | 0.62 | 18.15 |
| 4–6 | 16 (23) | 16 (18) | 2.25 | 0.97 | 5.21 |
| 1–3 | 24 (34) | 54 (62) | Ref | — | — |
| Number of ticks found biting or stuck on body | |||||
| 4 or more | 34 (48) | 8 (9) | 33.05 | 9.92 | 155.12 |
| 3 | 8 (11) | 6 (7) | 10.65 | 2.63 | 58.14 |
| 2 | 10 (14) | 20 (23) | 4.17 | 1.19 | 17.89 |
| 1 | 16 (23) | 25 (29) | 5.27 | 1.63 | 21.50 |
| 0 | 3 (4) | 28 (32) | Ref | — | — |
| Tick bite reaction | |||||
| Bites from a tick created a mark or took longer than usual to heal | 55 (67) | 20 (11) | 7.93 | 3.74 | 16.80 |
| Bites from a tick did not create a mark or take a long time to heal | 17 (21) | 49 (26) | Ref | — | — |
| Information about tick bite reaction not applicable or missing | 10 (12) | 122 (64) | — | — | — |
| Antibodies reactive to Rickettsia rickettsii and/or Ehrlichia chaffeensis | |||||
| Yes | 14 (17) | 18 (9) | 2.00 | 0.90 | 4.20 |
| No | 68 (83) | 173 (91) | Ref | — | — |
Abbreviations: LCL, lower confidence limit; OR, odds ratio; Ref, reference; UCL, upper confidence limit.