Introduction: Infectious complications following solid organ transplantation (SOT) are associated with significant morbidity and mortality in children, especially among the younger ones in whom infections are the single most common cause of early death. Adult data cannot be extrapolated to children given the immaturity of their immune system, the lack of exposure to many pathogens before immunosuppression and the increased exposure to common pathogens related to their behavior. We aimed to evaluate the burden and timeline of infections in the first year following pediatric SOT in the Swiss Transplant Cohort Study (STCS.
Methods: All SOT recipients aged 0-18 years at time of SOT enrolled in the STCS between 2008 and 2020, with at least one year of follow up, were included in this retrospective study. All clinically relevant infectious disease events (IDE), matching ID definitions previously defined by the STCS infectious disease working group and occurring during the first year after SOT were collected.  For each IDE, time after transplantation, patient’s age, the type of transplant and the outcome were analyzed. Four age groups were defined: (0-1), (1-5) (5-12) and (12-17 years).
Results: 271 pediatric SOT recipients were included with a median age at transplantation of 8.6 years (IQR:1.82-14.7). Demographics are presented in Table 1.19/271 patients (7%) had a shorter follow-up period due to loss of graft, death. 104/271 patients (28.4%) were treated for at least one rejection episode during the study period.
Among 271 patients, 134 patients (49%) presented at least one IDE with a total of 302 relevant IDE identified. The majority of ID event occurred during the first month after SOT (94/302; 31%).The ID rate/person/year was 1.19.Viral infections were predominant (159/302; 53%), with 2/3 being proven viral disease (105/159), whereas bacterial and fungal infections represented 42% (125/302) and 6% (18/302) of IDE, respectively.
Regarding organ specificities, the IDE rate was higher in liver transplant recipients (1.85 IDE/person/year), compared to other single organs (all< 1.00 IDE/person/year). The ID rate for multiple SOT was 33.3 IDE/person/year. Viral IDE predominated in liver transplant recipients (59%) whereas bacterial IDE predominated in kidney and lung transplant recipients (50%). The cumulative incidence by organ and age is presented in figure 1A and 1B. Together, the ID events of the first and second age groups constituted 58% of the ID events total (175/302).
Conclusion: The burden of infection during the first year following pediatric transplantation is high, especially in liver transplant recipients and in younger children. Viral infections are most commonly associated with infection, probably reflecting the young age of liver transplant recipients.
Table 1: Demographics of the cohort