Lab Matters Fall 2024 | Page 110

APHL 2024 POSTER ABSTRACTS

Using Secondary Analyses to Identify Aberrant Test Positivity Rates on Rapid Molecular Platforms in Wisconsin

M . Martin 1 , T . Davis 2 , S . Buechner 2 , M . Wedig 2 , A . Bateman 2 , Centers for Disease Control and Prevention 1 , Wisconsin State Laboratory of

Hygiene 2

Background : The use of rapid molecular testing platforms that concurrently test for multiple pathogens causing similar symptoms has increased . These platforms can be beneficial to patient care and public health efforts when they rapidly identify pathogens causing illness , but inaccurate results can lead to poor clinical outcomes and affect surveillance estimates . In 2022 , bioMieurex , manufacturer of the BioFire ® [ BioFire Diagnostics , Inc ., Salt Lake City , Utah ] platform informed users that a software problem reported false positive Cryptosporidium results . Additionally , the Wisconsin State Laboratory of Hygiene ( WSLH ) and other Midwestern public health laboratories recently reported reduced confirmation of norovirus in specimens tested using BioFire ® , suggesting inaccurate BioFire ® norovirus results . We analyzed Cryptosporidium and norovirus data to evaluate a strategy for rapidly identifying testing inaccuracies .

Methods : De-identified summary testing data on respiratory and gastrointestinal pathogens are submitted to WSLH weekly by the Wisconsin Clinical Laboratory Network ( WCLN ), a partnership with approximately 130 clinical and public health laboratories . We analyzed Cryptosporidium and norovirus data submitted from WCLN laboratories from January 2018 , when BioFire ® use began to increase , through October 2023 . We calculated percent positivity for each pathogen by dividing number of positive tests by number of tests reported . Next , we compared percent positivity from BioFire ® testing with aggregate percent positivity using other platforms ( BD MaxTM [ Becton , Dickinson and Company , Franklin Lakes , New Jersey ], Cepheid GeneXpert ® [ Cepheid , Sunnyvale , California ]), Verigene ® [ Nanosphere , Inc ., Northbrook , Illinois ] and xTAG ® [ Luminex Corporation , Austin , Texas ]).

Results : During 2018 – 2023 , BioFire ® Cryptosporidium results reported to WCLN laboratories increased from 4,368 to 8,376 ; norovirus results increased from 4,332 to 7,526 . Results from other platforms increased from 5,480 to 10,734 for Cryptosporidium and from 7,575 to 9,511 for norovirus . Mean percent positivity for Cryptosporidium during 2018 – 2023 using BioFire ® ( 1.9 %, range : 1.4 %– 2.4 %) was similar , compared with other platforms ( 1.2 %, range : 0.9 %– 1.7 %). Mean percent positivity for norovirus during 2018 – 2021 using BioFire ® ( 6.3 %, range : 4.1 %– 8.2 %) was similar , compared with other platforms ( 6.1 %, range : 3.2 %– 8.8 %). However , norovirus percent positivity during 2022 – 2023 was nearly double using BioFire ® ( 9.1 %, range : 8.1 %– 10.1 %), compared with other platforms ( 5.1 %, range : 4.6 %– 5.6 %).

Conclusions : These results suggest that analyzing WCLN test positivity rates has the potential to rapidly identify instrument problems . Despite documented accuracy issues with BioFire Cryptosporidium detection , this analysis did not reveal differences in positivity rates for Cryptosporidium using BioFire ® , compared with other platforms . However , it did detect discordant norovirus positivity rates during 2022 – 2023 when comparing BioFire ® with other platforms . This finding supports evidence of BioFire ® norovirus testing inaccuracies based on laboratory reports of difficulty confirming positive norovirus BioFire ® test results . WSLH is considering employing this type of regular analysis to identify testing that requires further scrutiny .

Presenter : Matthew Martin , tqe7 @ cdc . gov

Validation of Hologic ® Specimen Transport Media as a Matrix Using the BioFire ® Respiratory Panel

J . van Loben Sels 1 , M . Lawrence 2 , T . Barnes 2 , J . Richards 2 , J . Dempsey 2 , C . Schjang 2 , B . Ellis 2 , Centers for Disease Control and Prevention 1 , VIDOH 2

Background : The US Virgin Islands ( USVI ) Territorial Public Health Laboratory ( TPHL ) diagnostic testing for respiratory disease is limited to SARS-CoV-2 , influenza and respiratory syncytial virus ( RSV ) using the Hologic Panther ® ( Hologic , Incorporated , Marlborough , Massachusetts ) System . To conduct surveillance concerning other pathogens , TPHL intends to use the BioFire ® ( bioMérieux Inc ., Marcyl ’ Étoile , France ) Respiratory Panel 2.1 ( RP2 ) to reflex-test samples that were negative using the Hologic Panther ® . Both standard viral transport media ( VTM ) and Hologic specimen transport media ( STM ) are approved matrices for the Hologic Panther ® , but STM is preferred because it provides increased specimen stability and biosafety . However , STM is not an FDA-approved matrix for RP2 . We validated STM to determine if it will be an acceptable matrix using BioFire ® RP2 for surveillance purposes .

Methods : Contrived specimens in both STM and VTM were generated for 23 respiratory pathogens included in the RP2 ( adenovirus , coronaviruses , metapneumovirus , rhinovirus , enterovirus , influenza viruses , parainfluenza viruses , Mycoplasma pneumoniae , Bordetella pertussis , Bordetella parapertussis and Chlamydia pneumoniae ). Ten samples for each pathogen were run according to manufacturer ’ s instructions . The positive and negative calls and areas under the melt curves were compared between matrices . The limit of detection ( LOD ) for each pathogen in both matrices was determined using titrations of contrived samples with known genome copy numbers and calculated by probit analysis .

Results : All 23 pathogens were detected in both STM and VTM with an accuracy and precision of 100 % across 10 replicates . The areas under the melt curves were comparable between the matrices , ranging from -7 % to 27 % larger in STM than VTM . However , this variability did not affect positive calls by RP2 . The type of matrix did not significantly affect LOD of any pathogen , because probit calculations of each LOD in VTM were within the 25 % range of LOD in STM .

Conclusions : Our results provide evidence that STM is an acceptable matrix using the BioFire ® RP2 . Based on these data , TPHL has incorporated RP2 into the test algorithm for expanded respiratory illness surveillance . When STM clinical specimens become available , we will validate STM using the diagnostic platform before reporting patient findings to clinicians in USVI .

Presenter : Jessica van Loben Sels , tri2 @ cdc . gov