Development of a national proficiency test for SARS-CoV-2 detection by PCR in Colombia.

Background: Proficiency testing (PT) is a tool for ensuring the validity of results of testing laboratories and is essential when laboratories are working with assays authorised for emergency use or implementing novel techniques for detecting emerging pathogens. Methods: In collaboration with the National Health Institute of Colombia and with international support, we developed a qualitative PT for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by reverse transcription polymerase chain reaction (RT-PCR). A proficiency test item (PTI) based on reference material (research grade) produced by the National Institute of Standards and Technologies (NIST) was prepared and characterised using three positive samples with varying concentrations of SARS-CoV-2 ribonucleic acid (RNA) and two negative (control) samples. Tests were distributed to 121 laboratories across the national network of public health laboratories in Colombia. Results: Positive samples had varying concentrations of SARS-CoV-2 RNA and were quantified by digital PCR (RT-ddPCR) assays for the E gene of SARS-CoV-2. We tested the ability of laboratories to detect low and high levels of viral RNA using samples with SARS-CoV-2 RNA concentrations of 1417 ± 216, 146 ± 28, and 14 ± 10 copies /uL (expanded uncertainty, k = 2, 95% confidence level) We also performed a semiquantitative analysis of instrumental responses (Ct values) reported by participating laboratories and homogeneity, stability, and characterisation studies of the produced materials to determine the adequacy of these materials and methods for use in the qualitative PT scheme. The PT evaluated reports for individual target genes from each laboratory; 98.3% of laboratories had satisfactory performance and the remaining 1.7% of laboratories had unsatisfactory performance for the detection of at least one of the reported genes. Conclusions: This PT scheme identified the potential metrological weaknesses of laboratories in the detection of SARS-CoV-2 by RT-PCR and may facilitate improvements in the quality of measurements from the perspective of public health surveillance.

Development of Avocado Reference Material for Pesticide Residue Analysis.

BACKGROUND: Pesticide quantitation in foods relies on the availability of matrix reference materials, which, however, are scarce because of the general instability of pesticides. In particular, no avocado reference material has been developed. OBJECTIVE: This research aimed to develop a reference material to support the determination of pesticide residues in avocado. METHOD: Avocado was spiked with 11 selected pesticides at levels of 0.01-0.35 mg/kg. The production process included the assessment of between-unit heterogeneity, stability during dispatch, and best storage conditions according to ISO 17034. Reference values were estimated through an interlaboratory comparison study involving laboratories of demonstrated competence and adhering to ISO/IEC 17025. The corresponding expanded uncertainties were calculated as 4-19% in compliance with the Guide to the Expression of Uncertainty in Measurement. RESULTS: The reference material was sufficiently homogeneous and stable at 4°C during the entire study period (365 days) for most of the pesticides, and at 40°C during 10 days, but it was unstable at 50 and 60°C during 10 days. Four pesticides showed downward trends; however, this behavior was considered in the uncertainty budget. As this material complied with all requirements of proficiency testing, it was used in an interlaboratory proficiency test designed to investigate analytical performance and assist laboratories in improving the quality of measurement results. CONCLUSIONS: The presented material can be used for the development of novel analytical methods or in-house reference materials and adds to the scarce supply of reference materials for the determination of pesticides in vegetable matrixes with high oil contents and intermediate water contents. HIGHLIGHTS: A novel reference material has been developed for the reliable and accurate quantitation of multiple pesticides in avocado, allowing researchers to avoid the preparation of in-house reference materials for this purpose.