Two New Tests for Respiratory Viruses Gain FDA Approval

According to the Centers for Disease Control and Prevention (CDC), flu season in the United States runs from November to early April and typically peaks in the month of February. Just in time for the worst of the cold and flu season, the US Food and Drug Administration (FDA) announced that it cleared for marketing two commercial tests that can screen for several different types of infectious respiratory viruses, including those responsible for many cases of influenza, also known as "flu." Both new tests use molecular methods to detect viral genetic material in samples from the respiratory tract of patients with symptoms. Respiratory viral testing can help diagnose the cause of symptoms and allow for early treatment of influenza with antiviral medications that can slow progression of the disease.

Currently, several different methods can be used to diagnose viral respiratory infections. (See the article on Influenza Tests for details.) Each has advantages and disadvantages. While some of these methods are very specific and can pinpoint the virus causing symptoms, they are time-consuming and results are available only after the time for treatment is past. Others give quicker results, often in a doctor's office, but may not determine the exact virus and may give positive results when the patient does not actually have the flu. Still others require expensive equipment and highly-trained personnel. The advantages of the new tests are that they can screen for and detect several different viruses simultaneously on a single sample relatively quickly.

The first molecular test, approved by the FDA on January 3 of this year, can screen for a panel of 12 different types of viruses. This method first performs a step called amplification in which many copies of the viral genetic material (if present in the sample) are produced. The amplified genetic material is then sorted so that the specific virus can be identified. This test detects influenza A, one of the most severe forms of the flu and differentiates it from influenza B, a less serious form of the disease. Other types of respiratory viruses detected by this test include:

• Respiratory syncytial viruses (RSV) - the main causes of respiratory infections that can lead to serious complications such as pneumonia in infants and infection of the airways leading to the lungs (bronchiolitis). This type of infection can contribute to the development of chronic pulmonary disease.
• Parainfluenza viruses 1, 2 and 3 - causes of the croup and upper respiratory symptoms
• Rhinovirus - source of common cold symptoms
• Adenovirus - causes infections similar to strep throat or tonsillitis
• Metapneumovirus - recently discovered respiratory virus

The second test, given FDA approval on January 18, can detect four respiratory viruses (influenza A virus, influenza B virus, and respiratory syncytial virus A and B) within a few hours in a single sample obtained from the secretions from the back of the throat of the patient. It also uses molecular methods and amplification to screen for these four viruses that are the leading causes of serious lower respiratory tract infections such as influenza, bronchiolitis, and pneumonia. This test would allow health care providers to quickly identify those that could benefit from early antiviral treatment.

Respiratory viral testing can be especially important to those most vulnerable to complications: the very young, the elderly, or those with compromised immune systems or preexisting diseases. The CDC estimates that the flu affects thousands of Americans each year and is a major cause of missed work. The CDC website states that "Every year in the United States, on average 5% to 20% of the population gets the flu, more than 200,000 people are hospitalized from flu complications, and about 36,000 people die from flu."

Notes of caution
Though these commercial tests have been cleared for marketing, don't expect to be able to request them the next time you visit your doctor with symptoms of the flu. The tests may prove to be relatively expensive, and insurance companies may not be ready to cover the cost. Though these tests may be useful in testing those susceptible to complications, they may not be cost effective to screen those who may be sick with the flu but may be able to get well on their own with simple supportive therapy, such as lots of rest and plenty of liquids. The FDA noted that both of these molecular tests do not rule out other infections or concurrent infections caused by other disease-causing agents, including bacteria. Additional testing such as cultures and X-rays may be necessary for a complete diagnosis.

Sources

S1
U.S. Food and Drug Administration. FDA News (January 3, 2008). FDA Clears First Test Designed to Detect and Identify 12 Respiratory Viruses from Single Sample. Available online at http://www.fda.gov/bbs/topics/NEWS/2008/NEW01770.html. Accessed February 2008.

S2
U.S. Food and Drug Administration. FDA News (January 18, 2008). FDA Clears for Marketing Real-Time Test for Respiratory Viruses. Available online at http://www.fda.gov/bbs/topics/NEWS/2008/NEW01780.html. Accessed February 2008.

S3
Centers for Disease Control and Prevention. The Flu Season. Available online at http://www.cdc.gov/flu/about/season/flu-season.htm. Accessed February 2008.

S4
Centers for Disease Control and Prevention. Key Facts about Influenza (Flu). Available online at http://www.cdc.gov/flu/keyfacts.htm. Accessed February 2008.

S5
(January 4, 2008) Manufacturer news release, Prodesse's Multiplex RT-PCR ProFlu+™ Assay Receives FDA Clearance. Available online at http://www.prodesse.com. Accessed February 2008.

S6
(January 3, 2008) Manufacturer news release, Luminex Corporation Receives U.S. Food and Drug Administration Clearance for xTAG(TM) Respiratory Viral Panel. Available online at http://phx.corporate-ir.net. Accessed February 2008.

Tests: Influenza Tests
Conditions: Lung Diseases

The Lung Association: Flu (influenza)
KidsHealth: Is It a Cold or the Flu?