Antigen Test Positivity After COVID-19 Isolation – Yukon-Kuskokwim Delta Region, Alaska
- Isolation is recommended during acute infection with SARS-CoV-2, the virus that causes COVID-19, but the duration of infectiousness varies among individual persons. Rapid antigen test results have been correlated with detection of viable virus (1-3) and might inform isolation guidance, but data are limited for the recently emerged SARS-CoV-2 B.1.1.529 (Omicron) variant.
- On January 5, 2022, the Yukon-Kuskokwim Health Corporation (YKHC) recommended that persons with SARS-CoV-2 infection isolate for 10 days after symptom onset (or, for asymptomatic persons, 10 days after a positive nucleic acid amplification or antigen test result).
- However, isolation could end after 5-9 days if symptoms were resolving or absent, fever was absent for ≥24 hours without fever-reducing medications, and an Abbott BinaxNOW COVID-19 Ag (BinaxNOW) rapid antigen test result was negative.
- Antigen test results and associated individual characteristics were analyzed among 3,502 infections reported to YKHC during January 1-February 9, 2022. After 5-9 days, 396 of 729 persons evaluated (54.3%) had a positive antigen test result, with a declining percentage positive over time.
- In a multivariable model, a positive antigen test result was more likely after 5 days compared with 9 days (adjusted odds ratio [aOR] = 6.39) or after symptomatic infection (aOR = 9.63), and less likely after previous infection (aOR = 0.30), receipt of a primary COVID-19 vaccination series (aOR = 0.60), or after both previous infection and receipt of a primary COVID-19 vaccination series (aOR = 0.17).
- Antigen tests might be a useful tool to guide recommendations for isolation after INDICAID Rapid Antigen Test Instructions SARS-CoV-2 infection. During the 10 days after infection, persons might be infectious to others and are recommended to wear a well-fitting mask when around others, even if ending isolation after 5 days.
Impaired detection of omicron by SARS-CoV-2 rapid antigen tests.

- Since autumn 2020, rapid antigen tests (RATs) have been implemented in several countries as an important pillar of the national testing strategy to rapidly screen for infections on site during the SARS-CoV-2 pandemic. The current surge in infection rates around the globe is driven by the variant of concern (VoC) omicron (B.1.1.529).
- Here, we evaluated the performance of nine SARS-CoV-2 RATs in a single-centre laboratory study. We examined a total of 115 SARS-CoV-2 PCR-negative and 166 SARS-CoV-2 PCR-positive respiratory swab samples (101 omicron, 65 delta (B.1.617.2)) collected from October 2021 until January 2022 as well as cell culture-expanded clinical isolates of both VoCs.
- In an assessment of the analytical sensitivity in clinical specimen, the 50% limit of detection (LoD50) ranged from 1.77 × 106 to 7.03 × 107 RNA copies subjected to the RAT for omicron compared to 1.32 × 105 to 2.05 × 106 for delta. To score positive in these point-of-care tests, up to 10-fold (LoD50) or 101-fold (LoD95) higher virus loads were required for omicron- compared to delta-containing samples.
- The rates of true positive test results for omicron samples in the highest virus load category (Ct values < 25) ranged between 31.4 and 77.8%, while they dropped to 0-8.3% for samples with intermediate Ct values (25-30).
Evaluation of the INDICAID COVID-19 Rapid Antigen Test in Symptomatic Populations and Asymptomatic Community Testing.
- As the COVID-19 pandemic progresses, there is an increasing need for rapid, accessible assays for SARS-CoV-2 detection. We present a clinical evaluation and real-world implementation of the INDICAID COVID-19 rapid antigen test (INDICAID rapid test).
- A multisite clinical evaluation of the INDICAID rapid test using prospectively collected nasal (bilateral anterior) swab samples from symptomatic subjects was performed. The INDICAID rapid test demonstrated a positive percent agreement (PPA) and negative percent agreement (NPA) of 85.3% (95% confidence interval [95% CI], 75.6% to 91.6%) and 94.9% (95% CI, 91.6% to 96.9%), respectively, compared to laboratory-based reverse transcriptase PCR (RT-PCR) using nasal specimens.
- The INDICAID rapid test was then implemented at COVID-19 outbreak screening centers in Hong Kong as part of a testing algorithm (termed “dual-track”) to screen asymptomatic individuals for prioritization for confirmatory RT-PCR testing.
- In one approach, preliminary positive INDICAID rapid test results triggered expedited processing for laboratory-based RT-PCR, reducing the average time to confirmatory result from 10.85 h to 7.0 h. In a second approach, preliminary positive results triggered subsequent testing with an onsite rapid RT-PCR, reducing the average time to confirmatory result to 0.84 h. In 22,994 asymptomatic patients, the INDICAID rapid test demonstrated a PPA of 84.2% (95% CI, 69.6% to 92.6%) and an NPA of 99.9% (95% CI, 99.9% to 100%) compared to laboratory-based RT-PCR using combined nasal/oropharyngeal specimens.
- The INDICAID rapid test has excellent performance compared to laboratory-based RT-PCR testing and, when used in tandem with RT-PCR, reduces the time to confirmatory positive result. IMPORTANCE Laboratory-based RT-PCR, the current gold standard for COVID-19 testing, can require a turnaround time of 24 to 48 h from sample collection to result.
- The delayed time to result limits the effectiveness of centralized RT-PCR testing to reduce transmission and stem potential outbreaks. To address this, we conducted a thorough evaluation of the INDICAID COVID-19 rapid antigen test, a 20-minute rapid antigen test, in both symptomatic and asymptomatic populations.
- The INDICAID rapid test demonstrated high sensitivity and specificity with RT-PCR as the comparator method.
- A dual-track testing algorithm was also evaluated utilizing the INDICAID rapid test to screen for preliminary positive patients, whose samples were then prioritized for RT-PCR testing. The dual-track method demonstrated significant improvements in expediting the reporting of positive RT-PCR test results compared to standard RT-PCR testing without prioritization, offering an improved strategy for community testing and controlling SARS-CoV-2 outbreaks.
Direct Detection of Feline Coronavirus by Three Rapid Antigen Immunochromatographic Tests and by Real-Time PCR in Cat Shelters
The aim of this study was the direct detection of feline coronavirus by real-time PCR and by three different rapid immunochromatographic (RIM) tests detecting antigens in faecal samples of shelter cats. Based on sensitivity and specificity calculated for each of the RIM tests, the utility of RIM tests was compared. Seventy faecal samples originating from shelter cats housed in quarantine were examined.
Out of 70 samples analyzed by real-time PCR, 44 (62.9%) were positive. Significantly more cats (p < 0.05) tested positive than negative. Neither age nor sex of the cats played a significant role (p > 0.05) in the shedding status of the virus.
TruStrip RDT Human Procalcitonin (PCT) Rapid Test cards, 25 tests/pack |
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PCT-RDT-25 | Alpha Diagnostics | 1 pack |
TruStrip RDT Human Serum Amyloid A (SAA) Rapid Test cards, 25 tests/pack |
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SAA-RDT-25 | Alpha Diagnostics | 1 pack |
Rat Rena-strip Kit, 25 tests |
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R-RENA-LF-025 | BioAssayWorks | 25 tests |
Human Rena-strip Kit, 25 tests |
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H-RENA-LF-025 | BioAssayWorks | 25 tests |
TruStrip RDT 5-minute Horse meat detection/adulteration rapid test cards, 25 tests/pk |
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RDT-6050H-25 | Alpha Diagnostics | 1 pk |
MTBK_20640-25 |
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AR02-P0011-25 | Abfrontier | 25ug |
Rv0351 (GrpE)-25 |
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AR02-P0003-25 | Abfrontier | 25ug |
Rv1009 (RpfB)-25 |
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AR02-P0006-25 | Abfrontier | 25ug |
Rv2450c (RpfE)-25 |
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AR02-P0007-25 | Abfrontier | 25ug |
Rv3875 (esxA)-25 |
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AR02-P0008-25 | Abfrontier | 25ug |
Rv2031c(HspX)-25 |
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AR02-P0009-25 | Abfrontier | 25ug |
Rv3131 (NfnB)-25 |
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AR02-P0010-25 | Abfrontier | 25ug |
26795 25 CLOSURE NTRL 25MM |
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26795-25 | CORNING | 50/pk |
Cardboard freezer box, hinged lid, insert for 25 snap-cap 5ml tubes, 5.25 x 5.25 x 3 inches |
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C2580-25 | MTC Bio | 5/pack |
AXYGEN® 25-WELL COMB FOR USE WITH 10 CM GEL BOX, 1.0 MM THICKNESS |
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HGB10-25-1 | CORNING | 1/pk |
AXYGEN® 25-WELL COMB FOR USE WITH 10 CM GEL BOX, 2.0 MM THICKNESS |
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HGB10-25-2 | CORNING | 1/pk |
AXYGEN® 25-WELL COMB FOR USE WITH 20 CM GEL BOX, 1.0 MM THICKNESS |
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HGB20-25-1 | CORNING | 1/pk |
TruStrip RDT Anthrax Protective antigen 83 (PA83) Rapid Test cards, 25/pk |
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800-100-RDT-25 | Alpha Diagnostics | 1 pk |
Mouse IL-25 ELISA Kit, 96 tests, Quantitative |
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MIL-025-170 | Alpha Diagnostics | 1 kit |
Amyloid Beta-peptide (25-35) (human) |
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A1039-25 | ApexBio | 25 mg |
Express Plasmid Midiprep Kit (25 min) |
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K1323-25 | Biovision | |
Express Plasmid Maxiprep Kit (25 min) |
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K1324-25 | Biovision | |
2.5x14 cellogel 250µ (25) |
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EHCA1200-ST06-25 | Consort | ea |
2.5x14 cellogel 200µ (25) |
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EHCA1200-ST07-25 | Consort | ea |
2.5x17 cellogel 250µ (25) |
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EHCA1200-ST11-25 | Consort | ea |
2.5x17 cellogel 200µ (25) |
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EHCA1200-ST12-25 | Consort | ea |
5.7x13 cellogel 250µ (25) |
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EHCA1200-ST29U-25 | Consort | ea |
5.7x14 cellogel 250µ (25) |
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EHCA1200-ST31-25 | Consort | ea |
5.7x14 cellogel 200µ (25) |
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EHCA1200-ST32-25 | Consort | ea |
5.7x14 cellogel 500µ (25) |
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EHCA1200-ST34-25 | Consort | ea |
Rv2769c (PE27 protein)-25 |
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AR02-P0001-25 | Abfrontier | 25ug |
25-place microscope slide box (for 75 x 25 mm slides) |
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PO202 | FD Neurotechnologies | each |
F-Box Only Protein 25 (FBXO25) Antibody |
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20-abx318182 | Abbexa |
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DiagNano Fluorophore Labeled Gold Nanoparticles, 25 nm |
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GFL-25 | Creative Diagnostics | 1 mL |
Agouti-related Protein (AGRP) (25-82), human |
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A1134-25 | ApexBio | 25 mg |
DiaEasy? Dialyzer (3 ml) MWCO 25 kDa |
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K1015-25 | Biovision | |
DiaEasy? Dialyzer (250 µl) MWCO 25 kDa |
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K1022-25 | Biovision | |
2.55x14.5 cellogel 250µ boskamp (25) |
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EHCA1200-ST57-25 | Consort | ea |
2.55x14.5 cellogel 200µ boskamp (25) |
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EHCA1200-ST58-25 | Consort | ea |
7.8x15 cellogel 250µ shandon (25) |
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EHCA1200-ST62-25 | Consort | ea |
7.8x15 cellogel 200µ shandon (25) |
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EHCA1200-ST63-25 | Consort | ea |
MTBK 20620 (PE protein)-25 |
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AR02-P0005-25 | Abfrontier | 25ug |
Melanocyte Associated Antigen gp 100 (17 - 25) |
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5-01532 | CHI Scientific | 4 x 5mg |
5.7x13 cellogel 250µ pratiga punched (25) |
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EHCA1200-ST29-25 | Consort | ea |
5.7x13 cellogel 200µ pratiga punched (25) |
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EHCA1200-ST30-25 | Consort | ea |
5.7x14 cellogel 250µ pratiga punched (25) |
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EHCA1200-ST42-25 | Consort | ea |
5.7x14 cellogel 200µ pratiga punched (25) |
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EHCA1200-ST43-25 | Consort | ea |
5.7x14 cellogel 500µ pratiga punched (25) |
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EHCA1200-ST45-25 | Consort | ea |
5.7x14.5 cellogel 200µ beckman punched (25) |
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EHCA1200-ST53-25 | Consort | ea |
2.55x14.5 cellogel 190µ boskamp hr (25) |
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EHCA1200-ST59-25 | Consort | ea |
7.8x15 cellogel 190µ shandon hr (25) |
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EHCA1200-ST64-25 | Consort | ea |
Rv0350 (Heat Shock Protein 70)-25 |
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AR02-P0002-25 | Abfrontier | 25ug |
Rv2299c (Heat Shock Protein 90)-25 |
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AR02-P0004-25 | Abfrontier | 25ug |
F-Box Only Protein 25 (FBXO25) Antibody (HRP) |
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20-abx309965 | Abbexa |
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F-Box Only Protein 25 (FBXO25) Antibody (FITC) |
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20-abx309966 | Abbexa |
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F-Box Only Protein 25 (FBXO25) Antibody (Biotin) |
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20-abx309967 | Abbexa |
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Single channel mini-pipette (130 mm) 25 ul, autoclavable |
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SCMP-25 | Alpha Diagnostics | 1 |
BasicExoRNA? Basic RNA extraction kit (Pre-isolated exosomes, 25 reactions) |
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K1222-25 | Biovision | |
5.7x14 cellogel 190µ for high resolution (25) |
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EHCA1200-ST33-25 | Consort | ea |
5.7x14 cellogel 190µ pratiga punched hr (25) |
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EHCA1200-ST44-25 | Consort | ea |
5.7x14.5 cellogel 190µ beckman punched hr (25) |
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EHCA1200-ST54-25 | Consort | ea |
RESERVOIR, POLYPROPYLENE, 25 ML, DIVIDED, NONSTERILE, BULK |
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RES-2CV-25 | CORNING | 100/pk |
PTPRF(His tagged) / LAR(His tagged)-25 |
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AR09-P0002-25 | Abfrontier | 25ug |
Melanocyte Associated Antigen gp 100 (17 25) Peptide |
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20-abx266049 | Abbexa |
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Large T antigen - rhesus polyomavirus 560-568 |
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A1078-25 | ApexBio | 25 mg |
surface antigen (208-215) [Hepatitis B Virus] |
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A1091-25 | ApexBio | 25 mg |
SARS-CoV-2 Antigen Rapid Test Kit |
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CoV2Ag-25 | UnScience | 25T/kit |
Cryo storage box, polycarbonate, for 25 (5x5) 5mL tubes |
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C2581 | MTC Bio | 5/pack |
Human F- box only protein 25, FBXO25 ELISA KIT |
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ELI-47425h | Lifescience Market | 96 Tests |
Mouse F- box only protein 25, Fbxo25 ELISA KIT |
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ELI-38493m | Lifescience Market | 96 Tests |
Bovine F- box only protein 25, FBXO25 ELISA KIT |
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ELI-30786b | Lifescience Market | 96 Tests |
Rat F box only protein 25(FBXO25) ELISA kit |
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E02F0285-192T | BlueGene | 192 tests |
Rat F box only protein 25(FBXO25) ELISA kit |
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E02F0285-48 | BlueGene | 1 plate of 48 wells |
Rat F box only protein 25(FBXO25) ELISA kit |
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E02F0285-96 | BlueGene | 1 plate of 96 wells |
Human F box only protein 25(FBXO25) ELISA kit |
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E01F0285-192T | BlueGene | 192 tests |
Human F box only protein 25(FBXO25) ELISA kit |
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E01F0285-48 | BlueGene | 1 plate of 48 wells |
Human F box only protein 25(FBXO25) ELISA kit |
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E01F0285-96 | BlueGene | 1 plate of 96 wells |
Rabbit F box only protein 25(FBXO25) ELISA kit |
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E04F0285-192T | BlueGene | 192 tests |
Rabbit F box only protein 25(FBXO25) ELISA kit |
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E04F0285-48 | BlueGene | 1 plate of 48 wells |
Rabbit F box only protein 25(FBXO25) ELISA kit |
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E04F0285-96 | BlueGene | 1 plate of 96 wells |
Mouse F box only protein 25(FBXO25) ELISA kit |
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E03F0285-192T | BlueGene | 192 tests |
Mouse F box only protein 25(FBXO25) ELISA kit |
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E03F0285-48 | BlueGene | 1 plate of 48 wells |
Mouse F box only protein 25(FBXO25) ELISA kit |
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E03F0285-96 | BlueGene | 1 plate of 96 wells |
Pig F box only protein 25(FBXO25) ELISA kit |
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E07F0285-192T | BlueGene | 192 tests |
Pig F box only protein 25(FBXO25) ELISA kit |
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E07F0285-48 | BlueGene | 1 plate of 48 wells |
Pig F box only protein 25(FBXO25) ELISA kit |
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E07F0285-96 | BlueGene | 1 plate of 96 wells |
Goat F box only protein 25(FBXO25) ELISA kit |
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E06F0285-192T | BlueGene | 192 tests |
Goat F box only protein 25(FBXO25) ELISA kit |
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E06F0285-48 | BlueGene | 1 plate of 48 wells |
Goat F box only protein 25(FBXO25) ELISA kit |
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E06F0285-96 | BlueGene | 1 plate of 96 wells |
Dog F box only protein 25(FBXO25) ELISA kit |
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E08F0285-192T | BlueGene | 192 tests |
Dog F box only protein 25(FBXO25) ELISA kit |
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E08F0285-48 | BlueGene | 1 plate of 48 wells |
Dog F box only protein 25(FBXO25) ELISA kit |
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E08F0285-96 | BlueGene | 1 plate of 96 wells |
Monkey F box only protein 25(FBXO25) ELISA kit |
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E09F0285-192T | BlueGene | 192 tests |
Monkey F box only protein 25(FBXO25) ELISA kit |
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E09F0285-48 | BlueGene | 1 plate of 48 wells |
Monkey F box only protein 25(FBXO25) ELISA kit |
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E09F0285-96 | BlueGene | 1 plate of 96 wells |
RESERVOIR, POLYPROPYLENE, 25 ML, V-BOTTOM, NONSTERILE, BULK |
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RES-V-25 | CORNING | 100/pk |
slingshot homolog 1 (SSH1)(MBP-his tagged)-25 |
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AR09-P0023-25 | Abfrontier | 25ug |
slingshot homolog 3 (SSH3)(MBP-his tagged)-25 |
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AR09-P0024-25 | Abfrontier | 25ug |
MHC class II antigen (45-57) [Homo sapiens] |
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A1081-25 | ApexBio | 25 mg |
DiagNano Fluorophore Labeled Gold Nanoparticles, 25 nm, Cellular Uptake |
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GFL-25-CU | Creative Diagnostics | 1mL |
The sensitivity of the RIM tests was found to be at low (<35%; RIM tests A and C) to satisfactory level (>50%, RIM test B). The number of virus particles determined by real-time RT-PCR analysis did not significantly correlate with the results detected by any of the RIM tests (p > 0.05). The results of this study indicate that the use of rapid antigen RIM tests in routine screening of FCoV shedding status in shelter cats is limited due to the occurrence of a high number of false negative results.