Table 3:

Hazard ratios for new resistance development with each additional day of exposure grouped by AP

	Adjusted hazard ratio (95% confidence interval)
	Any AP	Cefepime	Meropenem	Piperacillin-tazobactam
Each additional day of exposure	1.04 (1.04–1.05)a	1.08 (1.07–1.09)b	1.02 (1.01–1.03)c	1.08 (1.06–1.09)d
Sensitivity analyses (each additional day of exposure)e
Among patients with multiple follow-up culturesf	1.01 (1.01–1.02)g	1.07 (1.06–1.08)h	1.00 (0.99–1.01)i	1.05 (1.04–1.06)i
Among patients with ≥ 1 negative culture for AP resistance 60 days prior to cohort entry	1.01 (1.00–1.02)	1.22 (1.14–1.31)	1.02 (1.01–1.04)	1.10 (1.08–1.12)

AP: antipseudomonal beta-lactam

^aAdjusted for race, dementia, congestive heart failure, chronic obstructive pulmonary disease, cohort entry date relative to admission date (days), days in intensive care unit, mechanical ventilation days, central line days, and urinary catheter days

^bAdjusted for congestive heart failure, chronic obstructive pulmonary disease, days in intensive care unit, mechanical ventilation days, central line days, and urinary catheter days

^cAdjusted for age, chronic obstructive pulmonary disease, renal disease, cohort entry date relative to admission date (days), days in intensive care unit, mechanical ventilation days, and central line days

^dAdjusted for race, liver disease, diabetes, days in intensive care unit, mechanical ventilation days, central line days, and urinary catheter days

^eDetails regarding variables included in the multivariable models for the sensitivity analyses are listed in Appendix 2

^fSensitivity analysis accounting for possible surveillance bias by treating number of follow-up cultures as a time-varying exposure, then increasing the number until no significant difference existed between those with resistance and those censored

^gAmong patients with ≥ 6 follow-up cultures

^hAmong patients with ≥ 8 follow-up cultures

ⁱAmong patients with ≥ 3 follow-up cultures