Lab Matters Fall 2024 | Page 70

APHL 2024 POSTER ABSTRACTS

platforms . Validation included spiking heat / chemical inactivated virions from Zeptometrix of SARS-CoV-2 , influenza A and B , RSV and Mpox into wastewater influent matrix . Viral targets were recovered using Ceres Nanotrap microbiome magnetic affinity beads and RNA / DNA was extracted using the MagMax Viral Pathogen kit in conjunction with a Kingfisher Flex instrument . Extracts were analyzed on the QXONE and QIAcuity digital PCR platforms . The accuracy portion of the validation included 50 positive and 10 negative wastewater samples ( n = 60 ) for each target . Positive predictive and negative predictive values for each positive target ( n = 50 ) and negative target ( n = 10 ) was determined to be 100 %. Reproducibility was assessed with inter- and intra-operator and reagent variability experiments . Inter- and intra-experiments for the same target were similar on the same platform , but between platforms differed for FluA ( QXONE CV inter run 29 %, intra run 34 % vs QIAcuity CV inter run 19 %, intra run 20 %) and RSV ( QXONE CV inter run 22 %, intra run 22 % vs QIAcuity CV inter run 11 %, intra run 11 %). Limit of detection ( LOD ) was calculated using the lowest concentration of target template that was routinely ≥95 % positive . The manufacturers guidelines were used when assessing positivity ( two droplets for QXONE and three partitions for QIAcuity ). Limit of quantification ( LOQ ) was calculated using sample concentration that increased tenfold from the LOD and was determined to be between 70 and 350 copies / ml of wastewater which includes process losses from Ceres Nanotrap and nucleic acid extraction . An interlaboratory analysis was conducted with the Colorado Department of Public Health and Environment Wastewater Center of Excellence , comparing presence / absence and copies /µ l of target from the spiked accuracy samples ( n = 60 ), with results correlating across QXONE and QIAcuity platforms . The ability to simultaneously test for multiple pathogens across two platforms increases testing capacity , supporting the overall goal of improving infectious disease epidemiology and community health .

Presenter : Madeline Gilbert , maddie . gilbert @ doh . wa . gov

Evaluating a Multi-assay HIV Testing Algorithm

E . Kirkscey , R . Watkins , C . Nwankwo , H . Kidane , M . Williams , V . Amadi , C . Graggs , M . Shabazz , J . Stringer , L . Short , Dallas County Health and Human Services

Introduction : There are a multitude of diagnostic assays available for Human Immunodeficiency Virus ( HIV ). Each assay has a unique sensitivity and specificity and a testing algorithm that employs a variety of assays can compensate for individual test ’ s limitations and produce more reliable results . The Dallas County Health and Human Services Public Health Laboratory ( DCHHS PHL ) utilizes a strategic multi-assay algorithm to enhance diagnostic reliability by merging the strengths of three assays . The first test , a Bio-Rad BioPlex 2200 HIV Ag-Ab Assay , uses flow cytometry to detect HIV-1 and HIV-2 antibodies and p24 antigen . The next test , a Bio-Rad Geenius HIV ½ Supplemental Assay , uses an immunochromatographic assay to detect and differentiate between HIV-1 and HIV-2 antibodies . The final test , an Aptima HIV-1 Quant Dx Assay , uses the Hologic Panther system to perform nucleic acid amplification testing to detect HIV-1 RNA . The testing workflow starts with the BioPlex assay . All non-reactive samples receive confirmatory testing via the Aptima assay . BioPlex assay-reactive samples receive follow-up testing via the Geenius assay . Non-reactive Geenius assay samples are confirmed via Aptima assay . All Aptima and reactive Geenius assay results are deemed conclusive . This study was performed to evaluate the DCHHS PHL HIV testing algorithm ’ s efficacy by comparing the final results generated by the overall algorithm and its constituent assays .

Methods : A comparative analysis of BioPlex , Geenius and Hologic assay results was conducted on HIV-reactive sample data from February 1 to December 31 , 2023 . BioPlex assay results were matched to corresponding Geenius and Aptima assay results by sample identification number . Samples that did not adhere to the testing algorithm were excluded from the study . Data was compiled using Horizon Laboratory Information System queries .

Results : Out of 326 BioPlex assay-reactive samples , 290 samples confirmed as reactive via Geenius assay . Nine of the 36 Geenius assay-non-reactive samples were reactive via Aptima assay . The remaining 27 Geenius assay-non-reactive samples were also nonreactive via Aptima assay . This indicates an 8.3 % false positive rate for the initial BioPlex assay screening . Conversely , the BioPlex assay generated 17,069 non-reactive samples and six of the non-reactive BioPlex assay samples were reactive upon Aptima assay testing . This indicates a 0.035 % false negative rate .

Conclusion : The comparative analysis reveals the DCHHS PHL multiassay algorithm testing strategy enhances HIV diagnostic accuracy . By integrating assays with different testing methods , the algorithm corrected for 27 false positive and six false negative HIV samples from February to December of 2023 . Employing a multi-assay algorithm significantly increases DCHHS PHL ’ s ability to contribute to public health in the Dallas-Fort Worth Metroplex .

Presenter : Eleanor Kirkscey , Eleanor . Kirkscey @ dallascounty . org

Evaluation of Aztreonam-avibactam MIC Test Strips Against Reference Broth Microdilution for Enterobacterales

R . Balbuena 1 , J . Ilutsik 2 , L . Curtis 2 , M . Machado 1 , M . Karlsson 3 , J . Rasheed 1 , Centers for Disease Control and Prevention 1 , Goldbelt C 62 , Goldbelt C 6 / Centers for Disease Control and Prevention 3

Introduction : Aztreonam ( ATM ) is a monobactam antibiotic stable in the presence of metallo-β-lactamases . Avibactam ( AVI ) is a β-lactamase inhibitor capable of protecting ATM from any coproduced serine β-lactamases . For this reason , the combination of ATM-AVI is recommended by multiple experts in the treatment of severe Gram-negative infections ; however , the combination is still pending FDA approval . In the present study , we evaluated the performance of the ATM-AVI gradient diffusion test strip ( MTS , Liofilchem ) by comparing it against reference broth microdilution ( BMD ).

Methods : A total of 94 Enterobacterales isolates from the CDC & FDA Antibiotic Resistance ( AR ) Isolate Bank were used to perform a side-by-side comparison of MTS and BMD . Of the 94 isolates with minimum inhibitory concentrations ( MICs ) ranging from 0.03 to 64 , 45 isolates harbored one or more carbapenemase gene , including metallo-β-lactamases genes ( blaNDM , blaVIM and blaIMP ). Reference antimicrobial susceptibility testing was performed using in-house-prepared , frozen BMD panels according to Clinical and Laboratory Standards Institute ( CLSI ) guidelines . On the BMD panel , the ATM concentrations ranged from 0.03 to 64 µ g / mL with AVI fixed at 4 µ g / mL . The MTS included ATM concentrations from 0.016 to 256 µ g / mL with AVI at a fixed concentration of 4 µ g / mL . Two