Table 2.
Effect Modification by Sex of the Association Between Invasive Group B Streptococcus Disease and Mortality.
| Single Reference Category Analyses | Stratified Analyses | ||||
|---|---|---|---|---|---|
| Cohorts | Mortality Rate per 1000 Person-Years | HR (95% CI) for iGBS Using a Common Reference Group | Effect Modification on Additive Scale (Interaction Contrast [95% CI]); AP [%] | HR (95% CI) for iGBS Within Strata of Sex | Effect Modification on Multiplicative Scale (P Value of GBS × Sex) |
| Denmark | |||||
| 0–89 days | |||||
| GBS–/Girls | 73.7 (60.1–87.4) | 1.00 (reference) | 1.00 (reference) | ||
| GBS+/Girls | 98.1 (48.4–147.7) | 0.87 (0.51–1.49) | 0.89 (0.52–1.53) | ||
| GBS–/Boys | 63.5 (52.1–74.9) | 1.04 (0.81–1.35) | 1.00 (reference) | ||
| GBS+/Boys | 100.6 (55.4–145.9) | 1.16 (0.71–1.88) | 12.8 (–56.7 to 82.2); 12.7% | 1.08 (0.67–1.76) | P = .52 |
| 0–5 years | |||||
| GBS–/Girls | 4.4 (3.7–5.2) | 1.00 (reference) | 1.00 (reference) | ||
| GBS+/Girls | 6.5 (3.6–9.4) | 0.97 (0.60–1.57) | 1.00 (0.62–1.62) | ||
| GBS–/Boys | 3.8 (3.1–4.4) | 1.01 (0.80–1.29) | 1.00 (reference) | ||
| GBS+/Boys | 5.3 (2.9–7.6) | 1.01 (0.62–1.63) | –0.6 (–4.5 to 3.3); NA | 0.97 (0.60–1.57) | P = .90 |
| The Netherlands | |||||
| 0–89 days | |||||
| GBS–/Girls | 71.7 (52.4–91.0) | 1.00 (reference) | 1.00 (reference) | ||
| GBS+/Girls | 340.7 (204.4–477.0) | 4.33 (2.67–7.02) | 4.33 (2.67–7.01) | ||
| GBS–/Boys | 72.0 (54.8–89.3) | 1.24 (0.87–1.79) | 1.00 (reference) | ||
| GBS+/Boys | 302.7 (188.5–416.8) | 4.76 (2.99–7.57) | –38.3 (–218.0 to 141.4); NA | 3.82 (2.44–5.97) | P = .71 |
| 0–5 years | |||||
| GBS–/Girls | 4.6 (3.4–5.8) | 1.00 (reference) | 1.00 (reference) | ||
| GBS+/Girls | 20.2 (12.1–28.3) | 3.81 (2.37–6.14) | 3.81 (2.36–6.13) | ||
| GBS–/Boys | 4.6 (3.6–5.7) | 1.17 (0.83–1.65) | 1.00 (reference) | ||
| GBS+/Boys | 18.8 (12.0–25.7) | 4.85 (3.10–7.58) | –1.4 (–12.1 to 9.3); NA | 4.14 (2.70–6.36) | P = .80 |
HRs are adjusted for matching variables (birth year, gestational age). Due to absence of cases in the extreme preterm age category (<28 weeks), the preterm age categories were merged (<37 weeks) for adjustment purposes.
Abbreviations: AP, attributable proportion; CI, confidence interval; HR, hazard ratio; iGBS, invasive group B Streptococcus disease; NA, not applicable.