Table 5. Impact on direct medical cost* due to cohort year, Lyme disease (LD) diagnosis groups, diagnostic and treatment procedures, and patient characteristics in Maryland Eastern Shore (regression results, n = 3,415).
| Direct medical cost (US$) | 5th CI† (US$) | 95th CI (US$) | p | |
|---|---|---|---|---|
| Baseline cost‡ | 60.88 | 55.94 | 66.26 | <0.0001 |
| Additional direct medical cost§ | ||||
| Clinically early stage | 34.93 | 22.59 | 50.65 | <0.0001 |
| Clinically late stage | 67.05 | 45.57 | 94.97 | <0.0001 |
| Suspected LD | 3.16 | -0.68 | 7.96 | 0.171 |
| Other LD-relevant complaint | 8.33 | 4.28 | 13.29 | <0.0001 |
| Serologic test¶ | 38.27 | 28.20 | 50.59 | <0.0001 |
| Procedure# | 26.13 | 17.68 | 36.58 | <0.0001 |
| Hospitalization/emergency room (ER)** | 114.96 | 89.85 | 145.83 | <0.0001 |
| Consultation†† | 84.68 | 68.09 | 104.56 | <0.0001 |
| Therapy‡‡ | 36.66 | 29.15 | 45.56 | <0.0001 |
| Miscellaneous§§ | 46.96 | 38.21 | 57.27 | <0.0001 |
| Erythema migrans¶¶ | -9.56 | -13.02 | -4.90 | <0.0001 |
| Male | -0.68 | -2.72 | 1.84 | 0.571 |
| Each year of age## | 0.11 | 0.05 | 0.19 | <0.0001 |
| Year 1998 | -5.05 | -9.28 | 0.54 | 0.0003 |
| Year 1999 | -12.74 | -15.11 | -9.50 | 0.0371 |
| Year 2000 | -9.09 | -12.09 | -5.08 | <0.0001 |
*Direct medical costs of LD included costs of physician visits, consultation, serologic testing, procedure, therapy, hospitalization/ER, and other relevant costs. Patients were divided into 5 diagnosis groups: clinically defined early-stage LD, clinically defined late-stage LD, suspected LD, tick bite, and other related complaints. All costs were converted to 2000 equivalent. †CI, confidence interval. ‡Baseline costs refer to those costs accrued by a female patient who had tick bite only (with no erythema migrans symptoms), diagnosed in 1997 during an office visit. She had no hospital or ER stay, no serologic tests, no consultation, no therapy, and no other procedures (R2 = 0.67). §Additional direct medical costs are added or subtracted to the baseline costs for each variable of interest if significant (see Appendix 3 for details). ¶Serologic test (yes = 1, no = 0) refers to patients who had serologic test (e.g., enzyme-linked immunosorbent assay or Western blotting test). #Procedure (yes = 1, no = 0) refers to patients who had other procedures that were not performed in hospital/ER, consultation, or physician office. **Hospitalization/ER (yes = 1, no = 0) refers to patients who had hospital or ER stay. ††Consultation (yes = 1, no = 0) refers to patients who received consultation from other physicians. ‡‡Therapy (yes = 1, no = 0) refers to patients who had therapy charges including antimicrobial agents and additional costs associated (e.g., registered nurse home visits). §§Miscellaneous (yes = 1, no = 0) refers to patients who had other appropriate charges such as charges for additional laboratory tests. ¶¶ Refers to patients with erythema migrans (yes = 1, no = 0). ##Age is a continuous variable and refers to each additional year of age of the patient.