Table 2. Protective effect of a first typhoid visit against recurrent typhoid due to reinfection in the total population (n = 70,566).
| No. of individuals | No. of typhoid visits | Person-days † | Incidence per 100,000 person-days | Crude HR ‡ | Adjusted Protective Effect (95% CI) ‡ | |
|---|---|---|---|---|---|---|
| Cohort 1 | 70566 | 315 | 86369890 | 0.36 | Ref |
Ref |
| All recurrent typhoid visits | ||||||
| Cohort 2 | 315 | 4 | 420965 | 0.95 | 5.37 (2.00, 14.43) | -200% (-708, -12) |
| Recurrent typhoid due to reinfection defined by SNP difference§ | ||||||
| Cohort 2 | 315 | 3 | 421740 | 0.71 | 4.00 (1.28, 12.50) | -124% (-599, 28) |
| Recurrent typhoid due to reinfection defined by antibiotic susceptibility∥ | ||||||
| Cohort 2 | 315 | 1 | 422584 | 0.24 | 1.33 (0.19, 9.46) | 26% (-429, 90) |
| Recurrent typhoid due to reinfection defined by intervening time¶ | ||||||
| Cohort 2 | 315 | 1 | 422653 | 0.24 | 1.33 (0.19, 9.46) | 26% (-427, 90) |
†In cohort 1, person-days calculated from study start date or date when person entered the study to end date, which is defined as date of study end, out-migration, or onset of the first typhoid visit. In cohort 2, person-days are calculated from the date of first typhoid visit to the date of study end, out-migration, death, or onset of the subsequent typhoid visit.
‡ Fitted a generalized proportional hazard model (AG model). The number of previous infections (0 or 1) was included in the model as a dummy variable; the reference group was the group without a previously detected typhoid visit. The risk was adjusted for Vi vaccination status as a time varying covariate and age at zero time.
§ Pairwise SNP difference >5
∥ Discordance in antibiotic susceptibility between infection pair >0
¶ Intervening period >30 days