As immunosuppressive drugs and allograft survival have improved over the last decades, infection has become the main hurdle of patient survival and long-term allograft function after renal transplantation. The knowledge of immunological and microbiological characteristics, however, remains scarce in renal transplant recipients developing sepsis.

We studied all adult renal transplant recipients at our transplant center transplanted between January 1, 2001, and December 31, 2010. 105 (10.4%) of 1013 patients, were diagnosed with sepsis. Early-onset sepsis (within 6 months after renal transplantation) was observed in 39.0% of cases, among which dynamics of monocytic HLA-DR expression and lymphocyte populations were analyzed.

Gram-negative microorganisms (57.4%) were the pathogens most commonly responsible, followed by gram-positive cocci (16.5%), and fungi (4.3%). Polymicrobic etiologic agents were detectable in 21.7% of cases. Urinary tract infections caused sepsis in 64% of the cases. Other portals of entry included the lung (14%), wounds (4%), the endocardium (3%), and miscellaneous sites (15%). The outcome of sepsis was fatal in 21.9% of the episodes. There was a significantly higher mortality for sepsis associated with pneumonia (72.2%) than urosepsis (6.1%; p<0.01). Simultaneous CMV reactivation was detected in 58.5% of cases with early-onset sepsis, but only 15.6% with late-onset sepsis (p<0.01), with significantly more CMV donor-positive/recipient-negative constellations (p=0.03). Simultaneous rejection was diagnosed in 31.7% of cases with early-onset sepsis, but only 4.7% with late-onset sepsis (p<0.01). Patients who died from sepsis, however, never showed concurrent allograft rejection (p=0.02). The use of lymphocyte-depleting agents for induction/rejection treatment was significantly higher in patients with early-onset sepsis (39.0% vs. 12.5%; p<0.01). Patients with immunological signs of sepsis-induced immune paralysis showed a rise in monocytic HLA-DR expression after reduction of immunosuppression (p<0.01).

The high mortality of sepsis in renal transplant recipients calls for careful attention to subtle immunological and microbiological characteristics denoting the onset and predicting the course of sepsis. In particular high-dose immunosuppression, concurrent CMV infection, and the use of lymphocyte-depleting antibodies apply for the increased risk early after renal transplantation.

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