Table 3. Adjusted risk ratios for primary RSV infection at age 1 and 2 years old by risk factor, England, 2008–2013 (n = 477)a .
| Risk factor | Adjusted risk ratios for primary RSV infection at age < 1 year old (95% CI)b | Adjusted risk ratios for primary RSV infection at age 1–2 years old (95% CI)b |
|---|---|---|
| Number of children included in the model | 477 | 229 |
| Number of infected children | 248 | 162 |
| Sex | ||
| Male (baseline) | 1 (baseline) | 1 (baseline) |
| Female | 1.07 (0.91–1.27) | 1.12 (0.95–1.32) |
| Ethnic group | ||
| White British (baseline) | 1 (baseline) | 1 (baseline) |
| Pakistani origins | 1.23 (0.98–1.55) | 0.88 (0.73–1.05) |
| Other | 1.27 (0.95–1.69) | 1.01 (0.80–1.28) |
| Annual quarter of birth | ||
| Jul–Sep (baseline) | 1 (baseline) | 1 (baseline) |
| Oct–Dec | 1.57 (1.19–2.08) | 1.23 (1.02–1.48) |
| Jan–Mar | 1.57 (1.18–2.09) | 1.12 (0.89–1.41) |
| Apr–Jun | 1.63 (1.22–2.18) | 0.77 (0.54–1.09) |
| Parity | ||
| 0 (baseline) | 1 (baseline) | 1 (baseline) |
| 1 | 1.49 (1.18–1.87) | 1.27 (1.04–1.56) |
| 2 | 1.22 (0.93–1.60) | 1.20 (0.93–1.56) |
| ≥ 3 | 1.38 (1.06–1.79) | 1.34 (1.05–1.70) |
| Attending any formal childcare | ||
| No (baseline) | 1 (baseline) | Not included in the final model |
| Yes | 1.36 (1.09–1.69) | |
| Age at measurementc | 1.08 (1.00–1.16) | 1.02 (0.96–1.08) |
CI: confidence interval; RSV: respiratory syncytial virus.
a Of 490 children whose blood samples were tested for immunoglobulin G antibody against RSV postfusion protein F, 477 (97%) had complete information for the analysis of risk factors for primary RSV infection at age <1 year old. Of these, 229 had not experienced an infection in infancy and were included for the analysis of risk factors for primary RSV infection at age 1–2 years.
b Risk ratios for primary RSV infection by each risk factor were estimated from Poisson regression models with robust error variances calculated using sandwich estimator.
c Age at measurement was centred around 12 months for risk ratios for primary RSV infection at age < 1 year, and around 24 months for risk ratios for primary RSV infection at age 1–2 years.