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Salmonella Typhi Antigen Rapid Test
Rapid S. Typhi Antigen Test is an in vitro qualitative immunochromatographic assay for the rapid detection of S. Typhi antigens in human stool or whole blood/plasma/serum specimen. The test results are intended to help in the diagnosis of S. Typhi infection and, to monitor the effectiveness of therapeutic treatment.
SUMMARY AND EXPLANATION
Typhoid fever is a life threatening illness caused by the bacterium Salmonella typhi, and was observed by Eberth (1880) in the mesenteric nodes and spleen of fatal cases of typhoid fever. It is common in developing countries where it affects about 12.5 million persons annually. The infection is acquired typically by ingestion. On reaching the gut, the bacilli attach themselves to the epithelial cells of the intestinal villi and penetrate to the lamina and submucosa. They are then phagocytosed there by polymorphs and macrophages. The ability to resist intracellular killing and to multiply within these cells is a measure of their virulence. They enter the mesenteric lymph nodes, where they multiply and, via the thoracic duct, enter the blood stream. A transient bacteremia follows, during which the bacilli are seeded in the liver, gall bladder, spleen, bone marrow, lymph nodes and kidneys, where further multiplication takes place. Towards the end of the incubation period, there occurs a massive bacteremia from these sites, heralding the onset of the clinical symptoms. The diagnosis of typhoid consists of isolation of the bacilli and the demonstration of antibodies. The isolation of the bacilli is very time consuming and antibody detection is not very specific. Other tests include the Widal reaction which lacks both sensitivity and specificity. Rapid S. Typhi Antigen Test takes only 10-20 minutes and requires only a small quantity of stool or one drop of serum* to perform. It is the easiest and most specific method for detecting S. typhi infection.
PRINCIPLE OF THE ASSAY
Rapid S. Typhi Antigen Test is a qualitative one step immunochromatographic assay. The test employs antibodies specific to S. typhi lipopolysaccharide (LPS) to selectively identify S. typhi (typhoid) infection with a high degree of sensitivity and specificity.
As the specimen flows through the absorbent pad in the sample well and through the antibody/colloidal gold complex any S. typhi antigen present in the sample binds to the conjugate forming an antigen/antibody complex. The sample and dye complex continue to migrate along the membrane to the test band region where Samonella specific LPS antibody is immobilized. In the presence of S. typhi, the antibody captures the complex. This forms a visible pink/purple band in the test band (T) or t of the card. If no antigen is present, there is no line formation in the (T) area. The remaining complex continues to migrate on the membrane to the control band (C) and forms a pink/purple band. The appearance of the control band indicates the proper performance of the test.
Each kit contains:
1. Rapid S. Typhi Antigen Test - 25 each
Each cassette contains a test strip with S. Typhi specific antibody on the test region of the membrane and colored S. Typhi antibody-gold conjugate pad.
2. Fecal sample buffer – 2 bottles, 8 mL each
3. Instruction for use
MATERIALS REQUIRED BUT NOT SUPPLIED
1. Specimen collection container
STORAGE AND STABILITY
1. The expiration date is indicated on the package label.
2. Test device can be stored at 4-30 °C.
1. This kit is for IN VITRO diagnostic use only.
2. This kit is for PROFESSIONAL use only.
3. Read the instructions carefully before performing the test.
4. This product does not contain any human source materials.
5. Do not use kit contents after the expiration date.
6. Handle all specimens as potentially infectious.
7. Follow standard Lab procedure and biosafety guidelines for handling and disposal of potentially infective material. When the assay procedure is completed, dispose specimens after autoclaving them at 121º C for at least 20 min. Alternatively, they can be treated with 0.5% Sodium Hypochlorite for 1-2 hours before disposal.
8. Do not pipette reagent by mouth and no smoking or eating while performing assays.
Wear gloves during the whole procedure.
SPECIMEN COLLECTION AND PREPARATION
1. Bring all reagents, including test device, to room temperature (15-30oC) before use.
2. Add about 1/4 gram to approximately 500μl of the extraction reagent provided (about 12 drops from the dropper vial provided). Mix well and allow to sit for 5 minutes or so to allow the large particles to settle.
3. QuickView™ S. Typhi Antigen Test can be run on stool or whole blood/plasma/serum samples.
The test works best on fresh samples. If testing cannot be done immediately, they should be stored at 2-8°C after collection for up to 3 days. If testing cannot be done within 3 days, serum can be stored frozen at –20°C or colder.
4. Shipment of samples should comply with local regulations for transport of etiologic agents.
5. Stool and whole blood/plasma/serum specimens should be collected in containers that do not contain media, preservatives, animal serum or detergents as any of these additives may interfere with the QuickView™ S. Typhi Antigen Test.
1. The control band is an internal reagent and procedural control. It will appear if the test has been performed correctly and the reagents are reactive.
2. Good Laboratory Practice recommends the daily use of control materials to validate the reliability of the device. Control materials are not provided with this test kit may be commercially available.
1. Bring all materials and specimens to room temperature (8 – 30°C).
2. Remove the test card from the sealed foil pouch.
3. For stool samples: use the provided pipet to transfer sample from the upper layer of the stool extract and add 2 drops to the sample well (marked as “S”).
For whole blood/plasma/serum samples: use the provided pipet to transfer the serum sample and add 2 drops to the sample well (marked as “S”).
4. Read the result at 20 minutes. A strong positive sample may show test band earlier. However, to confirm a result is negative, it must wait 20 minutes to read the results.
Note: The amount of S. typhi antigens present in whole blood/plasma/serum is typically less than that in stool. This may decrease the sensitivity of the test when using whole blood/plasma/serum specimens, depending how soon after the onset of the infection the test is performed. Early infection typically exhibits greater levels of the antigen in the whole blood/plasma/serum than in later infection.
To confirm whole blood/plasma/serum results: The use of a stool sample is recommended if whole blood/plasmaserum is used first and a negative result is obtained and typhoid is still suspected.
NTERPRETATION OF RESULTS
Positive result: A distinct pink colored band appears on test line regions, in addition to a pink line on the control line region.
Negative result: No line appears in the test line region. A distinct pink line shows on the control line region.
Invalid: The control line next to the test line does not become visible within 20 minutes after the addition of the sample.
LIMITATIONS OF THE PROCEDURE
1. The test is for qualitative detection of S.Typhi antigen in stool or whole blood/plasma/serum sample and dose not indicate the quantity of the antigens.
2. The test is for in vitro diagnostic use only.
3. For samples that test positive (reactive) by Rapid S. Typhi Antigen Test, more specific confirmatory testing should be done. A definitive clinical diagnosis should only be made by the physician after all clinical and laboratory finding have been evaluated.. The use of a rapid test alone is not sufficient to diagnose S. typhi infection even if antigen is present. Also, a negative result does not preclude the possibility of infection with S. typhi.
The analytical sensitivity of S. typhi test was determined at 25 ng/ml of LPS.
Negative stool samples and whole blood/plasma/serum specimens from patients in areas where typhoid is relatively rare and would yield a typical negative population, showed no false positives when the test was read within 20 minutes as specified.
Samples that were positive for s. paratyphi however were also negative as the antibodies used in the S. typhi rapid test are specific for S. typhi only.
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