Strep A Test Instructions

Strep A Antigen Rapid Test

Instruction for Use

A rapid test for the qualitative detection of Strep A antigens in throat swab specimens. For professional in vitro diagnostic use only.

 

INTENDED USE

The Strep A Antigen Rapid Test is a rapid chromatographic immunoassay for the qualitative detection of Strep A antigens from throat swab specimens to aid in the diagnosis of Group A Streptococcal infection.

 

SUMMARY

Streptococcus pyogenes is non-motile gram-positive cocci, which contains the Lancefield group A antigens that can cause serious infections such as pharyngitis, respiratory infection, impetigo, endocarditis, meningitis, puerperal sepsis, and arthritis.1 Left untreated, these infections can lead to serious complications, including rheumatic fever and peritonsillar abscess. Traditional identification procedures for Group A Streptococci infection involve the isolation and identification of viable organisms using techniques that require 24 to 48 hours or longer. The Strep A Antigen Rapid Test is a rapid test to qualitatively detect the presence of Strep A antigens in throat swab specimens, providing results within 5 minutes. The test utilizes antibodies specific for whole cell Lancefield Group A Streptococcus to selectively detect Strep A antigens in a throat swab specimen.

 

PRINCIPLE

The Strep A Antigen Rapid Test is a qualitative, lateral flow immunoassay for the detection of Strep A carbohydrate antigen in a throat swab. In this test, antibody specific to Strep A carbohydrate antigen is coated on the test line region of the test. During testing, the extracted throat swab specimen reacts with an antibody to Strep A that is coated onto particles. The mixture migrates up the membrane to react with the antibody to Strep A on the membrane and generate a color line in the test line region. The presence of this color line in the test line region indicates a positive result, while its absence indicates a negative result. To serve as a procedural control, a colored line will always appear in the control line region, indicating that proper volume of specimen has been added and membrane wicking has occurred.

 

REAGENT

The test contains Strep A antibody coated particles and Strep A antibodies coated on the membrane.

 

PRECAUTIONS

1. For professional in vitro diagnostic use only. Do not use after the expiration date.
2. Do not eat, drink or smoke in the area where the specimens and kits are handled.
3. Handle all specimens as if they contain infectious agents. Observe established precautions against microbiological hazards throughout the procedure and follow the standard procedures for proper disposal of specimens.
4. Wear protective clothing such as laboratory coats, disposable gloves and eye protection when specimens are assayed.
5. The used tests, specimens and potentially contaminated materials should be discarded according to local regulations.
6. Humidity and temperature can adversely affect results.
7. Do not use test if pouch is damaged.
8. Reagent B contains an acidic solution. If the solution contacts the skin or eye, flush with large volumes of water.
9. The positive and negative controls contain sodium azide (NaN3) as a preservative.
10. Do not interchange reagent bottle caps.
11. Do not interchange external control solution bottle caps.

 

STORAGE AND STABILITY

Store as packaged in the sealed pouch at room temperature or refrigerated (2-38°C). The test is stable through the expiration date printed on the sealed pouch. The test must remain in the sealed pouch until use. DO NOT FREEZE. Do not use beyond the expiration date.

 

SPECIMEN COLLECTION AND PREPARATION

1. Collect the throat swab specimen with the sterile swab that is provided in the kit. Transport swabs containing modified Stuart's or Amies medium can also be used with this product. Swab the posterior pharynx, tonsils and other inflamed areas. Avoid touching the tongue, cheeks and teeth with the swab.
2. Testing should be performed immediately after the specimens have been collected. Swab specimens may be stored in a clean, dry plastic tube for up to 8 hours at room temperature or 72 hours at 2-8°C.
3. If a culture is desired, lightly roll the swab tip onto a Group A selective (GAS) blood agar plate before using the swab in the Strep A Antigen Rapid Test.

 

MATERIALS

Materials Provided

• 25X Test device. Test cassette is individually sealed in a foil pouch with a package of desiccant.
• 25X Extraction tube with Colored Extraction reagent
• 25X Extraction tube with Colorless Extraction reagent
• 25X Swab
• 1 X Package insert

Materials Required But Not Provided

• Timer

 

ASSAY PROCEDURE

Allow the test, reagents, throat swab specimen, and/or controls to reach room temperature (15-30°C) prior to testing.

1. Remove the test cassette from the sealed foil pouch and use it within one hour. Best results will be obtained if the test is performed immediately after opening the foil pouch.
2. Hold the Colorless Extraction Reagent bottle vertically and add 4 full drops (approximately 160 uL) of Colorless Extraction Reagent to an extraction tube with Colored Extraction reagent. Mix the solution by gently swirling the extraction tube. The addition of Colorless Extraction Reagent to Colored Extraction Reagent changes the color of the solution from red to yellow. See illustration 1.
3. Immediately add the swab into the extraction tube, agitate the swab vigorously 15 times. Leave the swab in the extraction test tube for 1 minute.
4. Press the swab against the side of the tube and squeeze the bottom of the tube while removing the swab so that most of the liquid stays in the tube. Discard the swab. 
5. Fit the dropper tip on top of the extraction tube. Place the test cassette on a clean and level surface. Add three drops of the solution (approx. 120ul) to the sample well and then start the timer. Read the result at 5 minutes. Do not interpret the result after 10 minutes.

 

INTERPRETATION OF RESULTS

POSITIVE: Two lines appear. One colored line should be in the control line region (C) and another apparent colored line should be in the test line region (T). A positive result indicates that Strep A was detected in the specimen.

NOTE: The intensity of the color in the test line region (T) will vary depending on the concentration of Strep A present in the specimen. Therefore, any shade of color in the test line region (T) should be considered positive.

NEGATIVE: One colored line appears in the control line region (C). No line appears in the test line region (T). A negative result indicates that Strep A antigen is not present in the specimen, or is present below the detectable level of the test. The patient's specimen should be cultured to confirm the absence of Strep A infection. If clinical symptoms are not consistent with results, obtain another specimen for culture.

INVALID: Control line fails to appear. Insufficient specimen volume or incorrect procedural techniques are the most likely reasons for control line failure. Review the procedure and repeat the test with a new test. If the problem persists, discontinue using the test kit immediately and contact your local distributor

 

INTERNAL CONTROL

Internal procedural controls are included in the test. A colored line appearing in the control region (C) is an internal positive procedural control. It confirms adequate membrane wicking.

 

EXTERNAL CONTROL

It is recommended that a positive and negative external control be run every 25 tests, and as deemed necessary by internal laboratory procedures. External positive and negative controls are supplied in the kit. Alternatively, other Group A and non-Group A Streptococcus reference strains may be used as external controls. Some commercial controls may contain interfering preservatives; therefore, other commercial controls are not recommended.

 

LIMITATIONS

1. The Strep A Antigen Rapid Test is for in vitro diagnostic use only. The test should be used for the detection of Strep A antigen in throat swab specimens only. Neither the quantitative value nor the rate of increase in Strep A antigen concentration can be determined by this qualitative test.
2. This test will only indicate the presence of Strep A antigen in the specimen from both viable and non-viable Group A Streptococcus bacteria.
3. A negative result should be confirmed by culture. A negative result may be obtained if the concentration of the Strep A antigen present in the throat swab is not adequate or is below the detectable level of the test.
4. Excess blood or mucus on the swab specimen may interfere with test performance and may yield a false positive result. Avoid touching the tongue, cheeks, and teeth and any bleeding areas of the mouth with the swab when collecting specimens.
5. As with all diagnostic tests, all results must be interpreted together with other clinical information available to the physician.

 

EXPECTED VALUES

Approximately 15% of pharyngitis in children ages 3 months to 5 years is caused by Group A beta hemolytic Streptococcus. In school-aged children and adults, the incidence of Strep throat infection is about 40%. This disease usually occurs in the winter and early spring in temperate climates.

 

PERFORMANCE CHARACTERISTICS

Sensitivity and Specificity

The Strep A Antigen Rapid Test (Throat Swab) has been compared with another leading commercial rapid test using clinical specimens.

Method                   Results    Culture Positive    Culture Negative    Total Results
Strep A Ag Test Cassette Positive   180                6                   186
Strep A Ag Test Cassette Negative   9                  301                 310
Total Results                                       189                307                 496

Relative Sensitivity: 95.2% (91.2%-97.8%)*

Relative Specificity: 98.0% (95.8%-99.3%)*

Accuracy: 97.0% (95.1%-98.3%)*

* 95% Confidence Intervals

 

CROSS REACTIVITY

The following organisms were tested at 1.0 x 10^7 organisms per test and were all found to be negative when tested with the Strep A Antigen Rapid Test. No mucoid- producing strains were tested.

Group B Streptococcus, Neisseria meningitidis, Group F Streptococcus, Neisseria sicca, Streptococcus pneumonia, Branhamella catarrhalis, Streptococcus mutans, Group C Streptococcus, Staphylococcus aureus, Group G Streptococcus, Corynebacterium diphtheriae, Streptococcus sanguis, Candida albicans, Enterococcus faecalis, Serratia marcescens, Klebsiella pneumoniae, Bordetella pertussis, Neisseria gonorrhoeae, Neisseria subflava, Haemophilus influenzae, Staphylococcus epidermidis, Pseudomonas aeruginosa.

 

BIBLIOGRAPHY

1. Jeffrey N.Weiser, Daniela M. Ferreira, James C. Paton Streptococcus pneumonia transmission, colonization and invasion Nature Reviews Microbiology 16,355-367(2018)
2. Lance E. Keller, D. Ashley Robinson, Larry S. McDaniel capsulated Streptococcus pneumoniae: Emergence and Pathogenesis Aerican society for microbiology March/April 2016, 7, 2
   Bisno AL, Gerber MA, Gwaltney JM, Kaplan EL, Schwartz RH. Diagnosis and Management of Group A Streptococcal Pharyngitis. Clinical Infectious Diseases (1997), 25: 574-83.
3. RasmusMortensen, Thomas, Norrelykke, Nissen, Sine-Fredslund, Ida, Rosenkr adAldentifying protective Streptococcus pyogenes vaccine antigens recognized by both B and T cells in human adults and children, Scientific Reports 6, 22030 (2016)
4. Nussinovitch, M, Finkelstein Y, Amir J, Varsano, I. Group A beta-hemolytic streptococcal pharyngitis preschool children aged 3 months to to 5 years. Clinical Pediatrics (June 1999), 38: 357-360
5. Woods WA, Carter CT, Stack M, Connors Jr AF, Schlager TA. Group A Streptococcal Pharyngitis in Adults 30 to 65 years of age. Southern Medical Journal (May 1999), 491-492