Table 2. Comparison of models for the risk of acquiring third generation cephalosporin-resistant Klebsiella pneumoniae sensu lato over 864 patient days in a neonatal intensive care unit in Cambodia.
Models vary by explanatory variables (A-C) or by permitting the intercept to vary between study months in a hierarchical model (D). Models were fitted on the log-odds scale with a logit link function, hence prior distributions are shown as log-odds. Posterior parameter distributions have been transformed using the logistic function and are shown as probabilities. Prior distributions are normal distributions, shown in brackets are the mean and standard deviation respectively.
| Risk Factor Model | Parameters | Priors | Posterior Median (95% CrI)* |
WAIC† |
|---|---|---|---|---|
| (A) Single intercept Standard covariates‡ 96 hour antibiotic exposure |
α (intercept) β (slopes) |
normal(0, 10) normal(0, 5) |
0.23 (0.055, 0.60) ORs§ in results |
438 |
| (B) Single intercept Standard covariates‡ 48 hour antibiotic exposure |
α (intercept) β (slopes) |
normal(0, 10) normal(0, 5) |
0.26 (0.068, 0.63) Not shown |
441 |
| (C) Single intercept Standard covariates‡ + colonisation pressure term¶ 96 hour antibiotic exposure |
α (intercept) β (slopes) |
normal(0, 10) normal(0, 5) |
0.26 (0.059, 0.64) Not shown |
440 |
| (D) Intercept varies by month Standard covariates‡ 96 hour antibiotic exposure |
α[month] (intercept) μ (normal mean) σ (normal standard de- viation) β (slopes) |
normal(μ, σ) normal(0, 3) half-normal(0, 1) normal(0, 3) |
Varies by month††
0.21 (0.044, 0.57) 0.54 (0.51, 0.63) Not shown |
440 |
* 95% Credible interval. † Widely applicable information criterion (a model comparison statistic where lower values indicate better fitting models). ‡ Standard covariates: use of ampicillin, ampicillin + gentamicin, cloxacillin (oral), ceftriaxone, cloxacillin + gentamicin, and imipenem within the previous 48 or 96 hours; whether breast fed; receipt of an oral probiotic on entry (Lactobacillus acidophilus), sex, premature (born before the 37th week of pregnancy), severity (defined as severe if requiring ventilation, continuous positive airway pressure or inotopes), already colonised with 3GC-R E. coli, age in days on first admission to the NU, and the daily number of nurses on the ward. These explanatory variables were treated as binary and, where appropriate, time-varying. Covariates were recorded for every day the infant was present in the neonatal unit (see Methods for full details). § Odds ratios. ¶ Colonisation pressure is the number of known colonised patients on the ward on a given day. †† Median posterior probability ranges by month 0.20–0.23.