While obesity is considered a risk factor for worse survival after kidney transplant (KT), a single-center study reported that obesity has no direct effect on survival: instead, obesity leads to surgical site infection (SSI), and then SSI leads to worse survival. We examined the effect of SSI on obesity and survival using a national registry.

Methods: Using USRDS, we studied 92977 Medicare Primary KT recipients in 1999-2010. SSI was ascertained from Medicare inpatient claims during the 30 days post-KT using ICD-9 codes. We examined whether SSI fully mediates the association of obesity with patient/graft survival using these Cox models: base model (adjusted for basic confounders), base model stratified by occurrence of SSI, and base model adjusted for occurrence of SSI.

Results: In the base model, overweight (25-30 kg/m²), obese (30-35 kg/m²), and morbidly obese (>35 kg/m²) groups were at respectively 6%, 18%, and 25% higher hazards of death-censored graft loss than the normal weight (18.5-25 kg/m²) group (Table). The 30-day incidence of SSI was 3.7% overall; 2.3% in the normal weight, 3.3% in the overweight, 5.1% in the obese, and 8.2% in the morbidly obese group. When stratified by occurrence of SSI, obesity was associated with a higher hazard of graft loss among SSI(-) recipients (Table), suggesting a direct effect of obesity on graft loss regardless of SSI. This association was not observed among SSI(+) recipients. When adjusted for SSI, the association of obesity with graft loss did not notably differ from the base model (Table). In contrast, the hazard of death was significantly lower in the overweight and obese groups than the normal weight group by 8% and 7%, respectively (Table). Among the SSI(-) recipients, the overweight, obese, and morbidly obese groups were at lower hazards of death, but not among the SSI(+) recipients (Table). When adjusted for SSI, the association of obesity with death did not change notably (Table). SSI was associated with a higher hazard of graft loss and death (aHR=_1.381.49_1.61 and _1.371.47_1.57).

Conclusion: SSI is a risk factor for graft loss and death. Obesity is an independent risk factor for graft loss regardless of SSI.

CITATION INFORMATION: Bae S, Kucirka L, Massie A, Segev D. Surgical Site Infection Does Not Fully Explain the Impact of Obesity on Post-Transplant Outcomes. Am J Transplant. 2016;16 (suppl 3).

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