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Strep A (II)
Test
For the Rapid Qualitative
Detection of Group A Streptococcal Antigen from Throat Swabs
CLIA COMPLEXITY: Waived
This test is NOT AVAILABLE FOR RETAIL SALE.
FOR HEALTHCARE PROFESSIONAL PURCHASES ONLY.
INTENDED USE
The Strep A (II) Test is a lateral flow, one-step immunoassay for
the rapid, qualitative detection of Group A Streptococcal antigen
from throat swabs. The test is intended for use as an aid in the
diagnosis of Group A Streptococcal infection.
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SUMMARY
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 (Ref. 1). Conventional
methods used for the detection of the disease depend on the isolation
and subsequent identification of the organism (Ref. 1,2). These
methods often require 24-48 hours to complete. Recent developments
of immunological techniques (Ref. 3,4) which can detect Group A
Streptococcal antigen directly from throat swabs allow physicians
to diagnose and administer therapy immediately.
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TEST PRINCIPLE
The Strep A (II) Test utilizes a two-site sandwich immunoassay
technology for the detection of Group A Streptococcal antigen. The
test consists of a membrane strip which was pre-coated with rabbit
anti-Strep A antibody on the test line region and goat anti-rabbit
antibody on the control line region. A colored rabbit anti-Strep
A antibody-colloidal gold conjugate pad is placed at the end of
the membrane. During testing, the Strep A antigen is extracted from
the throat swab using the Extraction Reagent. The test strip is
then immersed in the extracted sample. The mixture then moves chromato-graphically
across the membrane to the immobilized rabbit anti-Strep A antibody
at the test (T) region. If Strep A antigen is present in the specimen,
a colored sandwich of solid phase/Strep A antigen/gold conjugate
is formed on the test region. Absence of the colored line at the
test (T) region indicates a negative result. Regardless of the presence
of Strep A antigen, as the extracted mixture continues to move laterally
across the membrane to the immobilized goat anti-rabbit antibody
control (C) region, a colored line at the control (C) region will
always appear. The presence of this colored line serves as: 1) verification
that sufficient volume has been added, 2) verification that proper
flow is obtained.
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STORAGE AND STABILITY
All reagents included in the Strep A (II) Test can be stored at
room temperature (15°-30°C) or refrigerated (2°-8°C)
until the expiration date printed on the kit box.
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PRECAUTIONS
- FOR IN-VITRO DIAGNOSTIC USE ONLY.
- FOR PROFESSIONAL AND LABORATORY USE ONLY.
- Do not mix reagents from different lots.
- Do not use after stated expiration date on the kit box.
- The Extraction Reagent is slightly caustic. Avoid contact with
eyes or mucous membranes. In the event of accidental contact,
wash thoroughly with water.
- If the Extraction Tube is missing the tablet, discard and use
another test pack.
- Positive and Negative Controls contain sodium azide which may
react with lead or copper plumbing to form potentially explosive
metal azides. When disposing of these solutions, always flush
with copious amounts of water to prevent azide build-up.
- Standard guidelines for handling infectious agents and chemical
reagents should be observed throughout all procedures. All contaminated
waste such as swabs, Strep A Test strips and extracts should be
properly disposed of.
- To obtain accurate results, package insert instructions must
be followed.
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REAGENTS AND MATERIALS SUPPLIED
- 25 test packs: Each pack contains one test strip with pre-coated
anti-Strep A antibody on the membrane and colored anti-Strep A
antibody pad, one plastic work station and one Extraction Tube
with a tablet inside. Each tablet contains 40 mg of sodium nitrite.
- Extraction Reagent: 0.5 M acetic acid (15 ml).
- Positive Control: Heat-killed Group A Streptococcus in solution
(1 x 10 8 organisms/ml) with 0.1 % sodium azide as preservative
(2 ml).
- Negative Control: Heat-killed Group B Streptococcus in solution
(1 x 10 8 organisms/ml) with 0.1 % sodium azide as preservative
(2 ml).
- 25 Sterile Throat Swabs.
- Instruction insert.
- Procedure card.
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SPECIMEN COLLECTION AND HANDLING
Follow standard clinical methods described by Facklam (Ref. 1)
and Ross (Ref. 5). To collect throat specimens, hold down the tongue
with a depressor and rub the swab on the tonsils, or any areas of
inflammation with the signs of pus or redness in the back of the
throat. Avoid contact with the tongue or sides of the mouth with
the swab.
It is recommended that swab specimens be processed as soon as possible
after collection. If swabs are not processed immediately they should
be placed into a dry, sterile, and tightly sealed plastic tube for
storage. Swab specimens can be stored at room temperature (15º-30ºC)
for up to 4 hours or refrigerated (2º-8ºC) for up to 24
hours. If a liquid transport method is employed, use modified Stuart's
Transport Media as outlined in the manufacturer's instructions.
Do not use char-coal or agar media.
Use of the supplied sterile rayon swabs with plastic shafts is
strictly required for Strep A (II) test. If a bacteria culture is
desired, gently streak the swab on a 5% sheep blood agar plate before
testing. The Extraction Reagent will kill the bacteria on the swab
and make it impossible to culture. Alternatively, a dual swab procedure
or a  subsequent
second swab specimen may be collected for the culture.
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TEST PROCEDURE
Notes:
- Review "specimen collection" instructions. Do not
open pouches until ready to perform the assay. Test reagents and
specimens should be brought to room temperature before testing.
- To avoid cross contamination, do not allow the tip of the reagent
bottle to come in contact with throat swabs or Extraction Tubes.
- Shake Extraction Reagent and Control bottles before use.
1. Open the foil pouch and place the Extraction Tube in the designated
areas of the workstation or tray. Remove the cap from the Extraction
Tube and add the Extraction Reagent up to the line marked on the
Extraction Tube.
2. Place the throat swab specimen in the Extraction Tube. Rotate
the swab against the tablet until it is dissolved.
3. Squeeze the swab firmly against the tube to expel as much liquid
as possible from the swab. Discard the swab.
4. Immerse the test strip into the Extraction Tube with the arrows
pointing toward the Extracted Sample Solution. Leave the test
strip in the Extraction Tube.
5. Read results in 5 minutes. Depending on the number of organisms
on the swab, positive results may be visible as soon as 1 minute.
However, to confirm a negative result the complete reaction time
of 5 minutes is required. Do not read results after 10 minutes.
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INTERPRETATION OF RESULTS
 Positive:
Two pink colored lines appear. In addition to a pink colored line
in the control (C) region, a pink colored line will also appear
in the test (T) region. The color intensities of the lines may vary.
A positive result indicates that the specimen contains Strep A antigen.
Negative:
Only one pink colored line appears in the control (C) region. No
apparent pink colored line is visible in the test (T) region. A
negative result indicates that there is no Strep A antigen in the
swab sample or that the Strep A antigen concentration is below the
detection level.
Invalid:
No pink colored line appears in the control (C) region. An absence
of the control line is an indication of procedural error or possible
reagent deterioration. A new test should be performed.
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QUALITY CONTROL
A procedural control is included in the test. A colored line appearing
on the control (C) region is considered an internal positive procedural
control, indicating proper performance. A clear background in the
result area is considered an internal negative procedural control.
If the reagents are working properly and the test has been performed
correctly, the background will clear to give a discernible result.
Positive Control:
Add Extraction Reagent to the line marked on the Extraction Tube.
Thoroughly mix the Positive Control by shaking the bottle vigorously.
Add 1 drop of Positive Control to the tube. Place a sterile swab
into the tube and swirl until the tablet is dissolved. Continue
with Test Procedure Step 3.
Negative Control:
Add Extraction Reagent to the line marked on the Extraction Tube.
Thoroughly mix the Negative Control by shaking the bottle vigorously.
Add 1 drop of Negative Control to the tube. Place a sterile swab
into the tube and swirl until the tablet is dissolved. Continue
with Test Procedure Step 3.
Note:
A Positive and Negative control must be tested when opening a new
test kit. Each operator performing testing within a test kit must
test a Positive and a Negative external control once with each 25-test
kit.
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LIMITATIONS
- The accuracy of the test depends on the quality of the swab
sample. False negatives may result from improper sample collection
or storage. A negative result may be obtained from patients at
the onset of the disease due to low antigen concentration. Therefore,
when a patient suspected of having Strep A infection has a negative
Strep A (II) Test result, additional testing using the culture
method is recommended.
- The test does not differentiate asymptomatic carriers of Group
A Streptococcus from those with infection. If clinical signs and
symptoms are not consistent with laboratory test results, a follow-up
throat culture method is required.
- In rare cases, test specimens heavily colonized with Staphylococcus
aureus can yield false positive results. If clinical signs and
symptoms are not consistent with clinical test results, a follow-up
culture procedure should be performed.
- Respiratory infections, including pharyngitis, can be caused
by Streptococci from serogroups other than Group A, as well as
by other pathogens.
- As with all diagnostic tests, a definitive clinical diagnosis
should not be based on the results of a single test, but should
only be made by a physician after all clinical and laboratory
findings have been evaluated.
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EXPECTED RESULTS
It is estimated that approximately 19% of all upper respiratory
tract infections are caused by Group A Streptococci (ref. 6). Infection
is most prevalent in winter and early spring, with most cases arising
in patients living in highly populated areas.
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PERFORMANCE CHARACTERISTICS
Detection Limit
To determine the analytical sensitivity of the Strep A (II) Test,
Group A Streptococcus bacteria were grown by standard culture technique.
The detection limit of the Strep A (II) Test was determined to be
2.5 x 10 5 organisms per test.
Correlation Study
A Correlation study of the Strep A (II) Test and the conventional
culture tests was carried out in a multi-center clinical evaluation.
One hundred and forty five (145) randomly selected throat swab
specimens were taken from children and adults exhibiting symptoms
of pharyngitis. The dacron swabs were used to inoculate blood agar
plates prior to testing with the Strep A (II) Test. Beta-hemolytic
colonies from the blood agar plates were confirmed as Group A Streptococcus
using serologic streptococcal grouping methods.
The results are summarized in the following tables. Clinical Sensitivity
and Specificity, and overall accuracy for Strep A (II) test are
calculated based on this data.
Sensitivity 90.2%
Specificity 98.1%
Overall Accuracy 95.8%
Specificity Study
To determine the specificity of the Strep A (II) Test to Group A
Streptococcal bacteria, the following Group A Streptococcal strains
at different levels of organisms per test were examined. Positive
results obtained at a level of 2.5 x 10 5 organisms/test for all
strains indicate that Strep A (II) Test is sensitive to all Group
A Streptococcal bacteria.
Group A Streptococcal Strains:
SS-091 SS-410 SS-492 SS-496
SS-633 SS-634 SS-635 SS-721
SS-754 SS-799 ATCC-19615
Cross-reactivity studies with organisms likely to be found in the
respiratory tract were also performed using the Strep A (II) Test.
The following organisms were tested at 1 x 10 8 organisms/test.
Group B Streptococcus
Group C Streptococcus
Group D Streptococcus
Group F Streptococcus
Group G Streptococcus
Pseudomonas aerugi-nosa
Streptococcus bovis Staphylococcus aureus
Proteus vulgaris Streptococcus faecalis
Staphylococcus epidermides Escherichia coli
Streptococcus faecium Streptococcus mitis
Corynebacterium diphtheriae Neisseria lactima
Neisseria gonorrhoeae Streptococcus salivarius
Streptococcus mutans Moraxella catarrhalis
Neisseria meningitidis Neisseria sicca
Staphylococcus saprophyticus Streptococcus sanguis
Streptococcus pneumoniae Candida albicans
Haemophilus parahaemolyticus Neisseria subflava
Bordetella pertussis
Negative results in all the above cases indicate that the Strep
A (II) Test is specific to Strep A bacteria only.
Physician Office Laboratory Studies
An evaluation of Strep A (II) Test was conducted at two Physician
Office Laboratory sites, using a panel of coded samples containing
Negative Control, Low Positive, Medium Positive and High Positive
specimens. Each specimen level was tested in replicates of five
at each site over a period of five days. One hundred percent (100%)
agreement to the expected results was obtained.
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