Salmonella Typhoid(S. typhi) IgG/IgM Rapid Test Cassette(WB/Sp

Salmonella Typhoid(S. typhi) IgG/IgM Rapid Test Cassette

Typhoid Test Intended Use

The Typhoid IgG/IgM Rapid Test is a lateral flow immunoassay for the simultaneous detection and differentiation of anti-Salmonella typhi (S. typhi)G and IgM in human serum or plasma. It is intended to be used as a screening test and as an aid in the  diagnosis of infection with S. typhi. Any reactive specimen with the  Typhoid IgG/IgM 2.0 Rapid Test must be confirmed with alternative testing method(s).

Summary and Explanation of  the Typhoid Test

Typhoid fever is caused by S. typhi, a Gram-negative bacterium. World-wide an estimated 17 million cases and 600,000 associated deaths occur annually¹. Patients who are infected with HIV are at significantly increased risk of clinical infection with S. typhi². Evidence of H. pylori infection also presents an increase risk of acquiring typhoid fever. 1-5% of patients become chronic carrier harboring S. typhi in the gallbladder.

The clinical diagnosis of typhoid fever depends on the isolation of S. typhi from blood, bone marrow or a specific anatomic lesion. In the facilities that can not afford to perform this complicated and time-consuming procedure, Filix-Widal test is used to facilitate the diagnosis. However, many limitations lead to difficulties in the   interpretation of the Widal test^3,4.                                

In contrast, the  Typhoid IgG/IgM Rapid Test is a simple and rapid laboratory test. The test simultaneously detects and differentiates the IgG and the IgM antibodies to S. typhi specific antigen⁵ thus to aid in the determination of current or previous exposure to the S. typhi.

Typhoid Test Principle

The Typhoid IgG/IgM Rapid Test is a lateral flow chromatographic immunoassay. The test cassette consists of: 1) a burgundy colored conjugate pad containing recombinant S. typhoid H antigen and O antigen conjugated with colloid gold (Typhoid conjugates) and rabbit IgG-gold conjugates, 2) a nitrocellulose membrane strip containing two test bands (M and G bands) and a control band (C band). The M band is pre-coated with monoclonal anti-human IgM for the detection of IgM anti-S. typhi, G band is pre-coated with reagents for the detection of IgG anti-S. typhi , and the C band is pre-coated with goat anti rabbit IgG.

When an adequate volume of test specimen is dispensed into the sample well of the cassette, the test specimen migrates by capillary action across the test cassette.  Anti-S. typhi IgM if present in the patient specimen will bind to the Typhoid conjugates. The immunocomplex is then captured on the membrane by the pre-coated anti-human IgM antibody, forming a burgundy colored M band, indicating a S. typhi IgM positive test result. 

Anti-S. typhi IgG if present in the patient specimen will bind to the Typhoid conjugates. The immunocomplex is then captured by the pre-coated reagents on the membrane, forming a burgundy colored G band, indicating a S. typhi IgG positive test result.

Absence of any test bands (M and G) suggests a negative result. The test contains an internal control (C band) which should exhibit a burgundy colored band of the immunocomplex of goat anti rabbit IgG/rabbit IgG-gold conjugate regardless of the color development on any of the test bands. Otherwise, the test result is invalid and the specimen must be retested with another device.

Typhoid Reagent and Materials Provided

1.       Each kit contains 25 or 30 test devices, each sealed in a foil pouch with three items inside:

        a. One cassette device.     

        b. One plastic dropper.

        c. One desiccant.

2.     Sample Diluent (1 bottle, 5 mL)

3.       One package insert (instruction for use).

Materials May Be required and not provide

1.       Positive Control (1 vial, red cap, 1 mL, Cat # R0160-P)

2.       Negative Control (1 vial, green cap, 1 mL, Cat # R0160-N)

Materials required but not provided

1.       Clock or Timer

Warnings and Precautions

For in Vitro Diagnostic Use

1.       This package insert must be read completely before performing the test. Failure to follow the insert gives inaccurate test results.

2.       Do not open the sealed pouch, unless ready to conduct the assay.

3.       Do not use expired devices.

4.       Bring all reagents to room temperature (15°C-30°C) before use.

5.       Do not use the components in any other type of test kit as a substitute for the components in this kit.

6.       Do not use hemolized blood specimen for testing.

7.       Wear protective clothing and disposable gloves while handling the kit reagents and clinical specimens. Wash hands thoroughly after performing the test.

8.       Users of this test should follow the US CDC Universal Precautions for prevention of transmission of HIV, HBV and other blood-borne pathogens.

9.       Do not smoke, drink, or eat in areas where specimens or kit reagents are being handled.

10.    Dispose of all specimens and materials used to perform the test as biohazardous waste.

11.    Handle the Negative and Positive Control in the same manner as patient specimens.

12.    The testing results should be read within 15 minutes after a specimen is applied to the sample well or sample pad of the device. Read result after 15 minutes may give erroneous results.

13.    Do not perform the test in a room with strong air flow, ie. an electric fan or strong air-conditioning.

Reagent Preparation and storage instructions

All reagents are ready to use as supplied. Store unused test devices unopened at 2°C-30°C.  The positive and negative controls should be kept at 2°C-8°C. If stored at 2°C-8°C, ensure that the test device is brought to room temperature before opening. The test device is stable through the expiration date printed on the sealed pouch. Do not freeze the kit or expose the kit over 30°C.

Limitations of Test

1.The Assay Procedure and the Test Result Interpretation must be followed closely when testing the presence of antibodies to S. typhi in serum or plasma from individual subjects. Failure to follow the procedure may give inaccurate results.

2.The  Typhoid IgG/IgM^2.0 Rapid Test is limited to the qualitative detection of antibodies to S. typhi in human serum or plasma. The intensity of the test band does not have linear correlation with the antibody titer in the specimen.

3.The  Typhoid IgG/IgM^2.0 Rapid Test also detects para-typhi antibodies.

4.A negative result for an individual subject indicates absence of detectable anti-S. typhi antibodies. However, a negative test result does not preclude the possibility of exposure to S. typhi.

5.A negative result can occur if the quantity of anti-S. typhi antibodies present in the specimen is below the detection limit of the assay, or the antibodies that are detected are not present during the stage of disease in which a sample is collected.

6. If the symptom persists, while the result from  Typhoid IgG/IgM^2.0 Rapid Test is negative or non-reactive result, it is recommended to re-sample the patient few days late or test with an alternative test method, such as bacterial culture method.

7.Some specimens containing unusually high titer of heterophile antibodies or rheumatoid factor may affect expected results.

8.The results obtained with this test should only be interpreted in conjunction with other diagnostic procedures and clinical findings.

References

1.Ivanoff BN, Levine MM, Lambert PH. Vaccination against typhoid fever: present status.  Bulletin of the World Health Organization 1994; 72: 957-71.

2.Gotuzzo E, Frisancho O, Sanchez J, Liendo G, Carillo C, Black RE, Morris JG. Association between the acquired immunodeficiency syndrome and infection with Salmonella typhi or Salmonella paratyphi in an endemic typhoid area. Archives of Internal Medicine 1991; 151: 381-2.

3.Clegg A, Passey M, Omena MK, et al. Re-evaluation  of the Widal agglutination test in response to the changing pattern of typhoid fever in the highlands of Papua New Guinea. Acta Tropica 1994;57:255-63

4.Pang T. False positive Widal test in nontyphoid Salmonella infection. Southeast Asian Journal of Tropical Medicine and Public Health 1989; 20: 163-4.

5. Ismail A, Hai OK, Kader ZA. Demonstration of an antigenic protein specific for Salmonella typhi. Biochem Biophys Res Commun.

Rebecca Yan 

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