# Monitoring bacterial contamination of blood components at the Croatian Institute of Transfusion Medicine—Evolution of strategies and results in a 14‐year period (2011–2024)

## TL;DR

This study tracks bacterial contamination rates in blood components at a Croatian transfusion center over 14 years, showing how testing strategies evolved and how contamination rates compare to other studies.

## Contribution

The study provides a detailed 14-year analysis of bacterial contamination trends and testing strategy evolution in blood components in Croatia.

## Key findings

- Bacterial contamination rate was 0.09% for quality control testing and 0.18% after universal screening implementation.
- Cutibacterium acnes was the most frequently detected organism in contaminated blood components.
- Testing strategies evolved to include universal screening for platelets using methods like large-volume delayed sampling.

## Abstract

This study presents the results and experiences of bacterial testing of blood components (BCs) at the Croatian Institute of Transfusion Medicine during the period 2011–2024.

During the 14‐year period, 74,283 BCs were tested. Among these, 20,231 components (8345 red blood cell concentrates, 5729 platelet concentrates [PCs] and 6157 plasma units) were tested as part of statistical quality control (QC). In addition, 100% bacterial screening was implemented for aphaeresis platelets in November 2019 and for pooled platelets in October 2022 with 17,187 aphaeresis platelets and 36,865 pooled platelets tested by the end of 2024. All pooled platelets were tested using the large‐volume delayed sampling (LVDS) method, whereas 9596 aphaeresis platelets were tested using the two‐step method (from November 2019 to November 2022) and 7591 using LVDS (from November 2022 to December 2024). BCs were sampled and inoculated into both aerobic and anaerobic culture bottles and incubated at 36 ± 1°C for 7 days.

As part of the statistical QC, 20,231 BCs (5729 PCs) were tested, resulting in a confirmed contamination rate of 0.09% (0.14% for PCs). Since the implementation of universal screening, 54,052 PCs have been examined, with a confirmed positivity rate of 0.18%. The most frequently detected organism was Cutibacterium acnes.

The confirmed positive rate of bacterial testing in our study and the isolates from positive cultures are comparable to similar studies. Active bacterial screening of BCs, among other measures, remains a critical step for preventing transfusion‐associated bacterial infections.