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The Directigen™ Flu A+B test is a rapid in vitro immunoassay membrane test for the direct and qualitative detection of influenza A and B viral antigens from nasopharyngeal wash, nasopharyngeal aspirate, nasopharyngeal swab, lower nasal swab, throat swab and bronchoalveolar lavage specimens of symptomatic patients. The Directigen Flu A+B test is a differentiated test, and therefore influenza A viral antigens can be distinguished from influenza B viral antigens in a single test. The test is to be used as an aid in the diagnosis of influenza A and B viral infections. All negative test results should be confirmed by cell culture because negative results do not preclude influenza virus infection and should not be used as the sole basis for treatment or other management decisions. The Directigen Flu A+B test is not intended for detection of influenza C.

Influenza is an acute viral disease that is seasonal in incidence. The illness classically presents with sudden onset of fever, chills, headache, myalgias, and a non-productive cough. Clinical manifestations usually resolve within one week unless complications develop. Influenza A or B virus cause the majority of clinically significant disease, with influenza C virus being responsible only for mild, predominately upper respiratory tract illness.

Patients who present with suspected influenza might benefit from treatment with antiviral agents. Amantadine¹ and rimantadine¹ are available for both the prevention and treatment of influenza A disease only. Zanamivir¹ and oseltamivir¹ are available for the treatment of both influenza A and B disease. In adults, therapy with these agents may reduce the severity and duration of illness if given within the first 48 h of onset of illness. Since the therapeutic options have expanded to include options for the treatment of influenza B disease, it is important to rapidly distinguish influenza A from influenza B in order to allow physicians a choice in selective antiviral intervention. Moreover, since only amantadine and rimantadine have indications for influenza prophylaxis, it is important to determine if influenza A is causing symptomatic disease in a particular institution (e.g., nursing home) or community, so that appropriate preventative intervention can be taken for susceptible individuals. It is therefore important to not only rapidly determine whether influenza is present, but also which type of influenza virus is present.

Procedures used to diagnose influenza type A and B infections include rapid immunoassay, direct specimen immunofluorescence assay, reverse transcription-polymerase chain reaction (RT-PCR), serologic assay, and culture isolation with confirmation.^2-8 Immunofluorescence assays entail staining of specimens immobilized on microscope slides using fluorescent-labeled antibodies for observation by fluorescence microscopy.^4,9,10 Culture methods employ initial viral isolation in cell culture, followed by hemadsorption inhibition, immunofluorescence, or neutralization assays to confirm the presence of the influenza virus.^10-12 The Directigen Flu A+B antigen detection test is an immunomembrane filter assay to detect influenza A or B antigens extracted from suitable specimens of symptomatic patients. Total test time is less than 15 min with reactivity determined by visual color development. Antigenic drift is not an issue with the Directigen Flu A+B test because the target antigens are the nucleoproteins, which are type-specific and are highly conserved.^13-15

The speed and workflow of Directigen Flu A+B make it applicable as a "STAT" influenza A and B antigen detection test, providing rapid, relevant information to assist with the diagnosis of influenza. The use of Directigen Flu A+B to differentiate Flu A from Flu B infection can provide the opportunity for greater selectivity of antiviral intervention.

Insert a DispensTube tip into the DispensTube. Vortex or mix thoroughly. NOTE: Do not use tips from other Directigen products.

Invert the DispensTube and holding the tube on the upper half, away from the tip, gently squeeze. NOTE: Squeezing the tube close to the tip may result in ejection of the tip and leakage of contents from the tube.

Dispense the extracted specimen dropwise (avoiding excess bubble addition), alternating single drops between the A and B test wells until 4 drops have been added to each well of the ColorPAC test device. Thus a total of 8 drops from each extracted specimen is added to a single test device.

When testing extracted Controls, the extracted Control A+/B- must be added to both wells of a single ColorPAC test device, and similarly, the extracted Control B+/A- must be added to both wells of a single ColorPAC test device.

Allow specimen to absorb completely.

If specimen fails to be absorbed into the device within five min, dilute as described in "Specimen Collection and Preparation" section and retest.

The following are included in the Directigen Flu A+B test kit.

For in vitro Diagnostic Use.

1. If infection with a novel influenza A virus is suspected based on current clinical and epidemiological screening criteria recommended by public health authorities, specimens should be collected with appropriate infection control precautions for novel virulent influenza viruses and sent to state or local health departments for testing. Viral culture should not be attempted in these cases unless a BSL 3+ facility is available to receive and culture specimens.

2. Pathogenic microorganisms, including hepatitis viruses, Human Immunodeficiency Virus and novel influenza viruses, may be present in clinical specimens. "Standard Precautions"^16-19 and institutional guidelines should be followed in handling, storing and disposing of all specimens and all items contaminated with blood and other body fluids. Prior to discarding, sterilize containers and other contaminated materials by autoclaving.

3. Differences in performance may be observed when this test is used on specimens from adults versus from children, but specific differences are not known.

4. Do not use reagents beyond the expiration date.

5. Do not mix reagents from different kit lot numbers or mix reagent bottle caps.

6. Do not reuse ColorPAC device. Incubation times and temperatures other than those specified may give erroneous results.

7. Hold reagent bottles vertically (approximately one inch from the ColorPAC membrane surface or tube), while gently dispensing one drop at a time, in quick succession to ensure proper drop delivery.

8. Avoid contact of reagents with skin and mucous membranes. If reagents come into contact with these areas, flush with water and contact your physician.

9. Reagents contain sodium azide, which is harmful if inhaled, swallowed or in contact with skin. Contact with acids liberates very toxic gas. If there is contact with skin, wash immediately with plenty of water. Sodium azide may react with lead and copper plumbing to form highly explosive metal azides. On disposal, flush with a large volume of water to prevent azide build-up.

10. Use polyester or rayon-tipped swabs with an aluminum wire for nasopharyngeal swabs (NPS). It has been determined that calcium alginate swabs can not be used with Directigen Flu A+B.

11. The Control A+/B- and Control B+/A- reagents have been prepared from recombinant cell cultures, not from viral cultures. Do not use the kit if the Control A+/B- and Control B+/A- reagents do not yield appropriate results.

12. Remove the ColorPAC device from the foil pouch just prior to use. Do not use if desiccant is missing from pouch.