BK polyomavirus (BKPyV) is a pathogen responsible for infectious complications in hematopoietic stem cell transplant (HSCT) recipients. This review aims to give an insight into recent data about the structure and genomic organization, epidemiology, clinical manifestations, diagnosis, and current treatment options of BKPyV infections in children after HSCT. News regarding viral replication and pathogenesis include the generation of miRNA, new mechanisms of viral shedding by releasing infectious particles via extracellular vesicles, and human bladder microvascular endothelial cells probably acting as viral reservoirs enabling low-level viral replication and persistence. In studies conducted over the past five years, BKPyV hemorrhagic cystitis (BKPyV-HC) has a prevalence rate of 4 to 27% in children undergoing HSCT. Diagnostics still has unsolved dilemmas like whole blood or plasma samples as well as the standardization of molecular methods to allow for reporting in international units. In terms of treatment, new approaches have been used in the past five years, including the use of mesenchymal stem cells (MSCs), virus-specific T cells (VSTs), and recombinant human keratinocyte growth factor (rH-KGF), although the efficacy of some of these treatments has only been documented in isolated studies. This complication continues to pose a substantial clinical challenge, characterized by an absence of effective preventive and therapeutic measures.

Background: Surgical site infections (SSIs) are among the most frequent healthcare-associated infections (HCAIs) worldwide. Changes in the functioning of healthcare systems may affect the implementation of SSIs prevention practices, with consequent alterations in the occurrence of HCAIs. The main aims of our study were to analyze specific SSIs prevalence and proportions together with overall HCAIs prevalence in acute care hospitals (ACHs) before and after the COVID-19 pandemic. Additional aims were to identify bacterial causative agents, the use of perioperative antibiotic prophylaxis (PAP), related structural and process quality indicators, and to determine trends between two periods. Methods: The National Reference Centre for HCAIs (University Hospital Centre Zagreb) conducted point prevalence surveys in May 2017 and May 2023 in ACHs throughout Croatia, using the technical protocol developed by the European Centre for Disease Prevention and Control (ECDC). Results: The prevalence of HCAIs in ACHs in Croatia rose from 5.3% (95% CI 4.8–5.7) in 2017 to 7.2% (95% CI 6.6–7.8) in 2023 (p = 9.93 × 10⁻¹⁴). This trend was paralleled with the rising of the HCAIs prevalence in surgical departments from 5.1% to 6.7% (p = 0.0099). The prevalence of overall SSIs across ACHs increased from 0.9% (95% CI 0.7–1.1) in 2017 to 1.2% (95% CI 1.0–1.5) in 2023 (OR 1.36 (1.03–1.80), p = 0.032. While the prevalence of superficial incisional SSIs significantly decreased (OR 0.53 (0.30–0.95), p = 0.028), the share of deep-seated SSIs (deep incisional and organ/space SSIs) among classified SSIs shifted from 48/92 to 77/96; odds ratio (OR) 2.09 (95% CI 1.45–3.01). In 2017, Gram-positive cocci were the most frequently isolated bacterial causative agents (44.6%). By 2023, this shifted, with Enterobacterales species comprising most isolates (42.2%). In 2023, significantly a higher proportion of patients received PAP (χ² = 25.419, df = 1, p < 0.5). An increase in the positive trend of alcohol-based hand rub antiseptics use in surgical departments (+15.7 L/patient-days, p < 0.001) contrasted with a decrease in infection prevention and control (IPC) nurses and medical doctors per hospital (−0.5, p = 0.041/−0.5, p = 0.003). Conclusions: Findings of the two point prevalence surveys over time indicate the changes in trends in surgical site infections burden, and highlight the need for the implementation and strengthening of preventive measures with the focus on targeted prevention of deep-seated infections.