Table 2.
Effect modification between age and BCG scarring on the risk of leprosy, Ciudad del Este, Paraguay, 2016–2017
| BCG scar | Age (yr) | OR (95% CI) for age within stratum of BCG1 | |||
|---|---|---|---|---|---|
|
| |||||
| ≥40 | <40 | ||||
|
|
|
||||
| Case/Control | OR (95% CI) | Case/Control | OR (95% CI) | ||
| Absent | 7/15 | 1.0 (reference) | 7/2 | 7.0 (1.2, 59.9) | 7.0 (1.2, 59.9) |
| p-value | 0.03 | 0.03 | |||
|
| |||||
| Present | 3/15 | 0.4 (0.1, 2.1) | 3/28 | 0.2 (0.0, 1.0) | 0.5 (1.0, 3.5) |
| p-value | 0.30 | 0.06 | 0.50 | ||
BCG, Bacillus of Calmette and Guérin; OR, odds ratio; CI, confidence interval.
1
Relative excess risk due to interaction=0.2–0.4–7.0+1.0=−6.2 (95% CI, −42.2 to −0.4); There is a negative interaction in the additive scale, also called sub-additive; Measure of interaction on the multiplicative scale= (0.2/0.4×7.0)=0.07 (95% CI, 0.10 to 0.87); There is a negative interaction in the multiplicative scale; The attributable proportion due to the interaction was −24.3 (95% CI, −100.0 to −3.2).