Strep A

Strep A
Strep A rapid tests are a well known method for the diagnosis of scarlet fever. The Strep A test is extremely sensitive, fast and accurate. The Strep A test enables you to perform a relable and cost-efficient screening.


The  Strep A Test Device is a rapid visual immunoassay for the qualitative, presumptive detection of Group A Streptococcus antigens in human throat swab specimens. This kit is intended for use as an aid in the diagnosis of Strep A infection.

INTRODUCTION

Beta-hemolytic Group A Streptococcus is a major cause of upper respiratory infections such as tonsillitis, pharyngitis, and scarlet fever. Early diagnosis and treatment of Group A Streptococcal pharyngitis has been shown to reduce the severity of symptoms and further complications, such as rheumatic fever and glomerulonephritis.

Conventional methods for detecting Strep A infection are dependent on isolation and subsequent identification of the organism, and often require 24 48 hours. Recent development of immunological techniques to detect Group A Streptococcal antigen directly from throat swabs allow physicians to diagnose and administer therapy immediately.

TEST PRINCIPLE

The Strep A Test Device detects Group A Streptococcus antigens through visual interpretation of color development on the internal strip. Anti-Strep A antibodies are immobilized on the test region of the membrane. During the test, the specimen reacts with polyclonal anti-Strep A antibodies conjugated to colored particles and precoated onto the sample pad of the test. The mixture then migrates through the membrane by capillary action and interacts with reagents on the membrane. If there is sufficient Strep A antigen in the specimen, a colored band will form at the test region of the membrane. The presence of this colored band indicates a positive result, while its absence indicates a negative result. The appearance of a colored band at the control region serves as a procedural control, indicating that proper volume of specimen has been added and membrane wicking has occurred.

TEST PROCEDURE

Bring tests, specimens, reagents and/or controls to room temperature (15-30°C) before use.

1. Prepare swab specimens:

• Place a clean extraction tube in the designated area of the workstation. Add 4 drops of reagent A to the extraction tube, then add 4 drops of reagent B. Mix the solution by gently swirling the extraction tube.

• Immediately immerse the swab into the extraction tube. Use a circular motion to roll the swab against the side of the extraction tube so that the liquid is squeezed from the swab and can reabsorb.

• Let stand for 1-15 minutes at room temperature, then squeeze the swab firmly against the tube to expel as much liquid as possible from the swab. Cap the extraction tube with the attached dropper tip. Discard the swab following guidelines for handling infectious agents.

2. Remove the test from its sealed pouch, and place it on a clean, level surface. Label the device with patient or control identification. For best results, the assay should be performed within one hour.

3. Add 3 drops (approximately 150 μl) of extracted solution from the extraction tube to the sample well on the test device.

Avoid trapping air bubbles in the specimen well (S), and do not add any solution to the observation window.

As the test begins to work, color will migrate across the membrane.

4. Wait for the colored line(s) to appear. The result should be read at 5 minutes. Do not interpret the result after 10 minutes.

PERFORMANCE CHARACTERISTICS

Analytical Sensitivity

To determine the analytical sensitivity of the DIMA® Strep A Test, Group A Streptococcus bacteria organisms were grown in broth culture. The detection limit of the DIMA® Strep A Test Device was determined to be 1.5×105 organisms per test.


Specificity Study

To determine the specificity of the Strep A Test Device to Group A Streptococcal bacteria, the following Group A Streptococcal Strains at different levels of organisms per test were examined. Positive results obtained at level of 1.5×105 organisms/test for all strains indicate that Strep A Test is sensitive to Group A Streptococcal bacteria.

Cross-reactivity studies with organisms likely to be found in the respiratory trace were also performed using the Strep A Test Device.
The following organisms were tested at 1×108 organisms/test.