Test Catalog

Test Id : STFRP

Shiga Toxin, Molecular Detection, PCR, Feces

Useful For
Suggests clinical disorders or settings where the test may be helpful

Sensitive, specific, and rapid detection of the presence of Shiga toxin-producing organisms such as Escherichia coli O157:H7 and Shigella dysenteriae type 1 in stool

 

This test is not recommended as a test of cure.

Testing Algorithm
Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

Special Instructions
Library of PDFs including pertinent information and forms related to the test

Method Name
A short description of the method used to perform the test

Real-Time Polymerase Chain Reaction (PCR) using Fluorescent Resonance Energy Transfer (FRET)

NY State Available
Indicates the status of NY State approval and if the test is orderable for NY State clients.

Yes

Reporting Name
Lists a shorter or abbreviated version of the Published Name for a test

Shiga Toxin PCR, F

Aliases
Lists additional common names for a test, as an aid in searching

E. coli O157:H7

Shiga producing E. coli

STEC

Testing Algorithm
Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

Specimen Type
Describes the specimen type validated for testing

Fecal

Additional Testing Requirements

In some cases, there may be local public health requirements that impact Mayo Clinic Laboratories (MCL) clients and require additional testing on specimens with positive results for this test. MCL recommends that clients retain an aliquot of each specimen submitted for testing to perform such additional testing, if needed. Alternatively (not preferred), clients who want their specimen returned from MCL should call MCL as soon as possible, at the latest within 96 hours of specimen collection, to request that MCL return an aliquot of the submitted specimen to them. Clients will be responsible for submitting their specimens to appropriate public health departments.

Necessary Information

Specimen source is required.

Specimen Required
Defines the optimal specimen required to perform the test and the preferred volume to complete testing

The high sensitivity of amplification by polymerase chain reaction requires the specimen to be processed in an environment in which contamination of the specimen by shiga toxin DNA is unlikely.

 

Submit only 1 of the following specimens:

 

Preferred:

Specimen Type: Preserved feces

Supplies: C and S Vial (T058)Container/Tube: Commercially available transport system specific for recovery of enteric pathogens from fecal specimens (15 mL of nonnutritive transport medium containing phenol red as a pH indicator, either Cary-Blair or Para-Pak C and S)

Specimen Volume: Representative portion of feces; 5 mL

Collection Instructions:

1. Collect fresh fecal specimen and submit in container with transport medium.

2. Place feces in preservative within 2 hours of collection.

Specimen Stability Information: Ambient (preferred) <7 days/Refrigerated <7 days

 

Acceptable:

Specimen Type: Unpreserved feces

Supplies:

-Stool container, Small (Random), 4 oz Random (T288)

-Stool Collection Kit, Random (T635)

Container/Tube: Fecal container

Specimen Volume: Representative portion of feces

Collection Instructions: Collect fresh fecal specimen and submit representative sample in fecal container.

Specimen Stability Information: Refrigerated (preferred) <7 days/Frozen <7 days

Special Instructions
Library of PDFs including pertinent information and forms related to the test

Forms

If not ordering electronically, complete, print, and send 1 of the following forms with the specimen:

-Microbiology Test Request (T244)

-Gastroenterology and Hepatology Client Test Request (T728)

-Renal Diagnostics Test Request (T830)

-Coagulation Test Request (T753)

Specimen Minimum Volume
Defines the amount of sample necessary to provide a clinically relevant result as determined by the Testing Laboratory

1 mL

Reject Due To
Identifies specimen types and conditions that may cause the specimen to be rejected

Formed feces or feces in gel transport medium
EcoFix preservative; formalin or PVA fixative
Preserved feces received frozen
Reject

Specimen Stability Information
Provides a description of the temperatures required to transport a specimen to the performing laboratory, alternate acceptable temperatures are also included

Specimen Type Temperature Time Special Container
Fecal Varies (preferred) 7 days

Useful For
Suggests clinical disorders or settings where the test may be helpful

Sensitive, specific, and rapid detection of the presence of Shiga toxin-producing organisms such as Escherichia coli O157:H7 and Shigella dysenteriae type 1 in stool

 

This test is not recommended as a test of cure.

Testing Algorithm
Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

Clinical Information
Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Shiga toxins (also known as Shiga-like toxins, Vero toxins, or Vero-like toxins) are encoded by some strains of Escherichia coli, most notably O157:H7. Shiga toxin can also be produced by other serogroups of enterohemorrhagic E coli (EHEC), as well as Shigella dysenteriae type 1. Generally, Shiga toxin-producing organisms cause bloody diarrhea, although this is not universal. Unlike some bacterial gastrointestinal infections, antimicrobial therapy is contraindicated, as antimicrobials may exacerbate disease. Treatment is primarily supportive (eg, hydration). A complication of infection by an organism producing Shiga toxin is hemolytic uremic syndrome (HUS). The percentage of people that develop HUS varies among outbreaks of E coli O157:H7, but generally ranges from 3% to 20%. HUS is characterized by a triad of findings: hemolytic anemia, thrombocytopenia, and kidney failure. Most people recover completely, however, some require permanent dialysis, and some die as a result of complications.

 

Several diagnostic methods that are available for the detection of EHEC lack sensitivity, are labor intensive, or have a long turnaround time. There are more than 160 serogroups of EHEC; the first serogroup to be associated with HUS was O157:H7. This is also the serogroup that is most commonly implicated in outbreaks. EHEC O157:H7 is detectable as non-fermenting colonies when cultured on sorbitol MacConkey (SMAC) agar, but the majority of non-O157:H7 Shiga toxin-producing E coli strains ferment sorbitol and, therefore, are undetectable by this method. The Vero cell line is susceptible to the Shiga toxin, but the assay can take up to 48 hours and is nonspecific. Commercial enzyme-linked immunosorbent assay (ELISA) antigen detection kits have a sensitivity of 90% when compared to culture, but an overnight enrichment step is necessary for adequate sensitivity. PCR detection of stx, the gene encoding Shiga toxin, directly from fecal specimens is a sensitive and specific technique, providing same-day results. PCR assay identifies non-O157:H7 Shiga toxin-producing bacteria, extending the utility beyond strains identifiable on SMAC agar.

Reference Values
Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Not applicable

Interpretation
Provides information to assist in interpretation of the test results

A positive polymerase chain reaction (PCR) result indicates the likely presence of Shiga toxin-producing Escherichia coli in the specimen. Although Shigella dysenteriae serotype 1 may produce a positive result, it is extremely rare in the United States.

 

A negative result indicates the absence of detectable Shiga toxin DNA in the specimen, but does not rule out the presence of Shiga toxin-producing E coli and may occur due to inhibition of PCR, sequence variability underlying primers or probes, or the presence of Shiga toxin DNA in quantities less than the limit of detection of the assay. Shiga toxins are encoded on mobile genetic elements and can theoretically be lost by their bacterial host.

Cautions
Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Interfering substances in the fecal specimen may affect the accuracy of this assay; results should always be interpreted in conjunction with clinical and epidemiological findings.

 

This assay detects stx subtypes stx1, stx2, stx2c, and stx2d. It does not detect stx2e or stx2f, which are seldom associated with human disease.

 

Repeat testing should not be performed on specimens collected less than 7 days apart.

Supportive Data

This assay was prospectively clinically validated using 204 stool specimens submitted for the antigen test (enzyme immunoassay: EIA method). In addition, the assay was used to test 85 archived fecal specimens previously tested for either Escherichia coli O157:H7 or Shiga toxin by EIA, with results compared to the prior results. Discordant results on the archived specimens were resolved by submission to the Minnesota Department of Health (MDH) for polymerase chain reaction (PCR) using different primers. Compared to a combined gold standard (ie, positive by EIA, culture, or MDH PCR) the Mayo PCR assay had 100% sensitivity and specificity; in total, 46 positive and 243 negative specimens were evaluated. No cross-reactivity was observed when tested on a panel of more than 50 organisms commonly found in stool. The analytical sensitivity was 2 targets/mcL.

Clinical Reference
Recommendations for in-depth reading of a clinical nature

1. Gould LH, Bopp C: Recommendations for diagnosis of Shiga toxin-producing Escherichia coli infection by clinical laboratories. MMWR Morb Mortal Wkly Rep. 2009 Oct;16:v58

2. Grys TE, Sloan LM, Rosenblatt JE, Patel R: Rapid and sensitive detection of Shiga toxin-producing Escherichia coli from nonenriched stool specimens by real-time PCR in comparison to enzyme immunoassay and culture. J Clin Microbiol. 2009;47:2008-2012

3. Grys TE, Patel R: Update on Shiga toxin-producing Escherichia coli. Mayo Clinic, Mayo Medical Laboratories Communique

4. Nyre LM, Kiemele DL, Zomok CD, et al: Clinical experience with rapid PCR for detection of Shiga toxin in stool. Abstract of the Annual Meeting of the American Society for Microbiology, 2010 General Meeting, San Diego, CA, May 23-27, 2010

5. Procop GW, Church DL, Hall GS, et al:The Enterobacteriaceae. In: Koneman’s Color Atlas and Textbook of Diagnostic Microbiology. 7th ed. Wolters Kluwer Lippincott Williams and Wilkins; 2017:213-315

Special Instructions
Library of PDFs including pertinent information and forms related to the test

Method Description
Describes how the test is performed and provides a method-specific reference

This method employs a target-specific detection system including polymerase chain reaction (PCR) primers, as well as fluorescent resonance energy transfer (FRET) hybridization probes designed for the stx1 and stx2 genes. The LightCycler instrument amplifies and monitors target nucleic acid sequences by fluorescence during PCR cycling. This is an automated PCR system that can rapidly detect amplified product development. The detection of amplified products is based on the FRET principle. For FRET product detection, a hybridization probe with a donor fluorophore, fluorescein, on the 3' end is excited by an external light source, which emits light that is absorbed by a second hybridization probe with an acceptor fluorophore, LC-Red 640, at the 5' end. The acceptor fluorophore then emits a light of a different wavelength that is measured with a signal that is proportional to the amount of specific PCR product. The process is completed in a closed tube system.(Grys TE, Sloan LM, Rosenblatt JE, Patel R: Rapid and sensitive detection of Shiga toxin-producing Escherichia coli from nonenriched stool specimens by real-time PCR in comparison to enzyme immunoassay and culture. J Clin Microbiol 2009;47:2008-2012)

PDF Report
Indicates whether the report includes an additional document with charts, images or other enriched information

No

Day(s) Performed
Outlines the days the test is performed. This field reflects the day that the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time before the test is performed. Some tests are listed as continuously performed, which means that assays are performed multiple times during the day.

Monday through Sunday

Report Available
The interval of time (receipt of sample at Mayo Clinic Laboratories to results available) taking into account standard setup days and weekends. The first day is the time that it typically takes for a result to be available. The last day is the time it might take, accounting for any necessary repeated testing.

1 to 2 days

Specimen Retention Time
Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded

7 days

Performing Laboratory Location
Indicates the location of the laboratory that performs the test

Rochester

Fees
Several factors determine the fee charged to perform a test. Contact your U.S. or International Regional Manager for information about establishing a fee schedule or to learn more about resources to optimize test selection.

  • Authorized users can sign in to Test Prices for detailed fee information.
  • Clients without access to Test Prices can contact Customer Service 24 hours a day, seven days a week.
  • Prospective clients should contact their Regional Manager. For assistance, contact Customer Service.

Test Classification
Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR) product.

This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information
Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Clinic Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.

CPT codes are provided by the performing laboratory.

87798

LOINC® Information
Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the order and results codes of this test. LOINC values are provided by the performing laboratory.

Test Id Test Order Name Order LOINC Value
STFRP Shiga Toxin PCR, F 80679-4
Result Id Test Result Name Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
SRC59 Specimen Source 31208-2
56052 Result 80679-4

Test Setup Resources

Setup Files
Test setup information contains test file definition details to support order and result interfacing between Mayo Clinic Laboratories and your Laboratory Information System.

Excel | Pdf

Sample Reports
Normal and Abnormal sample reports are provided as references for report appearance.

Normal Reports | Abnormal Reports

SI Sample Reports
International System (SI) of Unit reports are provided for a limited number of tests. These reports are intended for international account use and are only available through MayoLINK accounts that have been defined to receive them.

SI Normal Reports | SI Abnormal Reports