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Rapid Flu Tests May Prove Especially Helpful This Season

On October 5, Chiron Corporation notified the CDC that none of its influenza vaccine (Fluvirin) would be available for distribution in the United States for the current influenza season. In the wake of this sudden removal of nearly half of the anticipated American vaccine supply, medical officials and the general public have grown increasingly alarmed about the scarcity of vaccine and the risk of a looming epidemic.

It remains to be seen if virulent new strains of flu or an abnormally high incidence of the disease will strike when the nation is particularly vulnerable. No matter what measures public health officials activate to increase vaccine supplies and assure vaccination among the highest priority cohorts of the population, millions of Americans who would normally have a flu shot will be forced to go without this year.

Thus far this season, cases of influenza have been reported in 17 states, according to the weekly CDC report of October 23. This is likely the calm before the storm, because a typical flu season entails in excess of ten million cases of influenza in the U.S., causing some 200,000 hospitalizations and 36,000 deaths. With limited vaccine available, flu incidence and its impact this year could be far worse.

Given the situation, several steps have emerged as the best available courses of action:

1. Assure that available vaccine, including nasal-spray vaccines for appropriate age groups, are administered to those at highest risk: infants and young children, those with chronic or immuno-compromising diseases, pregnant women, residents of nursing homes the elderly and health care workers and caregivers.

2. Encourage reasonable hygiene precautions for everyone, including frequent and thorough hand washing. People are also being urged to remain home if they are experiencing flu-like symptoms.

3. Assiduously identify, track and treat flu outbreaks.

Diagnostic tests available for influenza inclu de reliable lab-based detection based on viral culture, serology, rapid antigen testing, polymerase chain reaction (PCR) and immunofluorescence testing. All are time-consuming, however, in a year when time is especially important.

Fortunately, three medical firms produce quick-results kits that have been CLIA-waived by the CDC for point-of-care use. With all of these products, higher sensitivity and specificity results are achieved with nasopharyngeal wash specimens than with NP swabs. The test kits include:

Binax, Inc., Portland, Maine, produces the NOW Flu A Test (Influenza A) and NOW Flu B Test (Influenza B), both of which, according to the company, are the most widely used products of their type in the market.

Quidel Corporation, San Diego, Calif., produces the QuickVue Influenza A+B test designed to detect the presence of the influenza A and B virus in a patient nasal wash or nasal swab sample within 10 minutes. Quidels technology utilizes the principle of antibody specificity for the influenza virus nucleoprotein (NP) to selectively interact with the influenza A and B viruses. The NP is evolutionarily conserved and not subject to the same year-to-year changes that make it necessary to be vaccinated each year to prevent influenza infection. For this reason the QuickVue test is not adversely affected by the appearance of different influenza strains.

ZymeTx Inc., Oklahoma City, Okla. Manufactures the ZstatFlu Rapid Test for Influenza A and B, the first point-of-care testing platform for the rapid diagnosis of Influenza A and B. and has proven specificity in diagnosing current strains of Influenza A and B in addition to all of the strains on record for the past 30 years.

The test uses a throat-swab specimen and requires about two minutes of tech time and 20 minutes processing time. It has a three-year shelf life and can be stored at room temperature.

Three other companies manufacture rapid result tests that are als o considered moderately complex by the College of American Pathologists, but are not currently CLIA-waived. These firms include:

Becton-Dickinson, Franklin Lakes, N.J., which produces the BD Directigen Flu A+B test kit, which the company says is the first rapid assay on the market that distinguishes influenza A viral antigens from those of influenza B. Specimen types that the kit can assess include nasopharyngeal wash, nasopharyngeal aspirate, nasopharyngeal swab, lower nasal swab, throat swab and bronchoalveolar lavage. Test results time is 15 minutes.

Thermo Electron Corp., Waltham, Mass., produces the FLU OIA test, a high-performance assay for the undifferentiated diagnosis of Influenza A and B. in just over 15 minutes. Assay advantages include superior performance with mucoid samples, specimen flexibility,and performance equivalent to 14-day viral culture, thus decreasing overall diagnostic costs by making additional ancillary testing unnecessary.

Finally, REMEL, Inc., Lenexa, Kan., produces Xpect Flu A & B kits for rapid chromatographic immunoassay for Influenza A and Influenza B viral antigens. This product is packaged in lots of 20.

Along with early detection, CDC is issuing interim recommendations for the use of antiviral medications during the 2004-05 season: amantadine and rimantadine for chemoprophylaxis and oseltamivir and zanamivir for treatment. While these medications provide welcome resources in trying circumstances, all carry some risk of side-effects and their supplies are limited in many areas

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