Table 5.
Cox proportional hazards model for 30-day mortality among patients at 3 hospitals (n = 845) included in a study of Staphylococcus aureus bacteremia, Los Angeles, California, 2012-2018 a
| Characteristic | Hazard ratio (95% CI) | P value b |
|---|---|---|
| Age | 1.03 (1.01-1.05) | .003 |
| Intensive care unit stay | 9.04 (4.26-19.14) | <.001 |
| ≥3 Comorbidities | 2.05 (1.09-3.85) | .03 |
| Pitt bacteremia score ≥4 c | 4.30 (2.49-7.44) | <.001 |
| SES class d | ||
| High-SES group vs low-SES group | — e | .60 |
| Intermediate-SES group vs low-SES group | — e | .31 |
| Distance of residence to hospital | — e | .01 |
| Distance of residence to hospital comparing high-SES group vs low-SES group | — e | .77 |
| Distance of residence to hospital comparing intermediate-SES group vs low-SES group | — e | .37 |
| Effect of 1-mile increase in distance between patient’s residence and hospital | ||
| High-SES group | 1.01 (0.99-1.03 f ) | NA |
| Intermediate-SES group | 0.99 (0.93-1.05 f ) | NA |
| Low-SES group | 1.02 (1.00-1.02 f ) | NA |
Abbreviations: NA, not applicable; SES, socioeconomic status.
Source of data: all data were extracted from medical records at each hospital.
P values determined by using the Kruskal-Wallis test or analysis of variance for continuous variables and χ2 or Fisher exact test for categorical variables. P ≤ .05 was considered significant.
The Pitt bacteremia score is widely used to determine the severity of illness caused by Staphylococcus aureus bacteremia; it ranges from 0 to 14 points, and a score ≥4 is commonly used to indicate critical illness. 14
Low SES includes people experiencing homelessness and SES quintile 1 (the quintile of people with the lowest SES), intermediate SES includes people in SES quintiles 2 and 3, and high SES includes people in SES quintiles 4 and 5 (the quintiles of people with the highest SES). SES classification was based on residential neighborhood defined at the 2010 census block–group level.
The hazard ratio entries for terms involved in interactions are not applicable. The individual hazard ratio corresponding to each of these effects depends on other variables in the interaction term of the model. Because of the interaction term in the model, each term comprising that interaction (such as SES class and distance) is represented by specification of additional covariates in the Cox proportional hazards model.
95% Wald confidence limits.