Table 1.
Factors associated with time to visible growth of L. interrogans strain NR-20157 on solid agara
| Culture condition | Univariable model |
Multivariable model |
||
|---|---|---|---|---|
| HRb (95% CI) | P value | HR (95% CI) | P value | |
| Concn (CFU/ml) of Leptospira inoculum | ||||
| 102 | 1.0 | <0.001 | 1.0 | <0.001 |
| 103 | 1.4 (0.9–2.0) | 1.6 (1.1–2.3) | ||
| 104 | 2.2 (1.5–3.2) | 3.3 (2.2–4.9) | ||
| 105 | 4.5 (3.0–6.6) | 11.3 (7.3–17.4) | ||
| Type of agar | ||||
| BA with 3% RS | 1.0 | <0.001 | 1.0 | <0.001 |
| BA with 5% RS | 1.2 (0.8–1.9) | 1.2 (0.8–1.9) | ||
| BA with 10% RS | 0.7 (0.4–1.1) | 0.5 (0.3–0.8) | ||
| Noble agar with 3% RS | 0.9 (0.6–1.4) | 0.8 (0.5–1.4) | ||
| Noble agar with 5% RS | 2.4 (1.6–3.8) | 3.7 (2.4–5.8) | ||
| Noble agar with 10% RS | 6.2 (3.9–9.9) | 15.2 (9.0–25.5) | ||
| No. of days of incubation in CO2c | ||||
| 0 | 1.0 | 0.15 | 1.0 | <0.001 |
| 1 | 1.7 (1.0–3.0) | 3.2 (1.8–5.8) | ||
| 2 | 2.0 (1.2–3.5) | 4.0 (2.3–7.0) | ||
| 3 | 1.6 (0.9–2.8) | 2.9 (1.6–5.1) | ||
| 4 | 1.4 (0.8–2.5) | 1.9 (1.1–3.4) | ||
| 5 | 1.7 (1.0.–3.0) | 2.3 (1.3–4.1) | ||
| Concn of CO2 (%)d | ||||
| 0 | 1.0 | 0.03 | NA | NA |
| 1 | 1.5 (0.9–2.5) | NA | ||
| 5 | 1.8 (1.1–3.0) | NA | ||
a
Abbreviations: BA, bacteriological agar base; HR, hazard ratio; RS, rabbit serum; NA, not applicable.
b
HR with 95% confidence interval (95% CI) represents the ratio of Leptospira growth rate compared to the baseline condition (for which HR = 1.0) over time. An HR value of more than 1.0 indicates that time to visible colonies for a given condition was shorter than the baseline condition, and vice versa.
c
Initial incubation in CO2 for 1 to 5 days was followed by incubation in air for a total of 28 days.
d
Concentration of CO2 was not a predictive factor in the multivariable model.