In the first year after transplant surgery, bacteria cause more than half of the infections that occur in solid organ transplant recipients. That's the result of a patient analysis conducted as part of the Swiss Transplant Cohort Study.

The information is important since it allows transplant teams to prescribe appropriate immunosuppressant drugs. Following an organ transplant, three periods of infection have been identified. First, up to a month after surgery, nosocomial infections and donor-derived infections occur. For up to six months, opportunistic infections occur. Lastly, a reduced phase of immunosuppression occurs with community-acquired and rare infections.

Identifying this pattern in 1998 allowed physicians to tailor prophylactic strategies, diagnostic testing and empiric therapies to solid organ transplant recipients. Indeed, immunosuppressive treatment plans have reduced not only rejection, but also lowered recipients’ risk of infections.

“Solid organ transplant (SOT) recipients require long-term immunosuppression and are at risk for life-threatening infections,” Dr. Christian van Delden of the Transplant Infectious Diseases Unit at the University Hospitals Geneva, and colleagues wrote. “Knowledge of timing and relative frequencies of infections in the era of extended donor/recipient criteria, modern immunosuppression, routine use of prophylaxis and active surveillance of viral replication is crucial for implementing prevention strategies to further reduce morbidity and mortality associated with post-transplant infections.”

The study was published in the Jan. 20, 2020, edition of the journal Clinical Infectious Diseases. The analysis included 93% of all solid organ transplant patients in Switzerland from May 2008 to December 2014 who had a minimum of 12 months of follow-up care. Adult lung, heart, liver, kidney and kidney-pancreas recipients were included in the study. Sixty-one percent of recipients were kidney transplant patients.

Of 1,520 patients, 3,520 experienced infections during the first year following transplant. Of those, 63% were caused by a bacterium. Enterobacteriaceae, as urinary pathogens in heart, lung and kidney transplant recipients and as digestive tract pathogens in liver transplant recipients, caused 54% of infections. Enterococcus species were seen in 20% of transplant infections and pseudomonas aeruginosa made up 9% of infections in lung transplant recipients.

"Better defining populations at risk for these opportunistic infections will be crucial to further improve the present prophylactic strategies, mostly designed for early infections," the authors wrote.

Virus accounted for a portion of the infections. Of the 1,039 viral infections, 51% were caused by herpes in kidney, liver and heart transplant recipients. More than 260 fungal infections occurred, with Candida species causing 60% of fungal infections among liver transplant recipients.

“The first month remains characterized by the highest burden of infections, with healthcare-associated infections prevailing. However, bacterial infections, mainly affecting the allograft and transplant site, continue at high rates throughout the entire year, urging for better control. The transplant-specific timelines presented here should help clinicians to target patient-adapted prophylactic and empiric treatments,” the authors concluded. “The high burden of Enterobacteriaceae, Pseudomonas and Enterococcus, with rising antimicrobial resistance, is worrisome and urges for the development of new approaches and antimicrobials to guarantee improved graft and patient survival.”