Sample Integrity in Respiratory Virus Surveillance: A Study on Volume Loss in Collection Kits at a Public Health Laboratory ^†

Introduction: Sample integrity is a critical factor for the reliability of molecular testing in public health laboratories, especially for epidemiological surveillance data. Inconsistent transport media volume and variations in swab quantity are common pre-analytical challenges that impact the quality and reproducibility of diagnostic results. This study investigated the impact of saline absorption by swabs and the variation in swab numbers, seeking evidence for the standardization and improvement of collection protocols in an active surveillance scenario. Methodology: For this study, six standardized collection kits were used. The initial volume was measured, and the swabs were inserted into the tubes for 24 h. After immersion, the remaining volume was transferred to a microtube and measured again, allowing us to quantify the solution loss. Additionally, we evaluated the impact of the number of swabs (one to three) on molecular test performance. Results: The analysis demonstrated a 37% average loss of the initial saline solution volume, with absorption by the swabs being the primary factor. A maximum variation of 51% in volume loss was observed in one of the kits. This significant volume reduction and the variation in the number of swabs (1 to 3) did not directly impact the molecular test results. Conclusions: The reduction in sample volume due to liquid absorption by swabs is an underestimated pre-analytical factor that can compromise the sensitivity and quality of molecular diagnostics. This study highlights the urgent need to standardize collection materials to ensure the reliability of surveillance data, which is essential for public health decision-making.