Monday, August 10, 2009

Rapid Tests for Detecting H1N1 Flu Not Reliable


Posted by Madeline Ellis on 7 Aug 2009

Officials estimate that since its emergence in early April, the H1N1 flu has infected as many as a million Americans. Its symptoms, which are similar to those of seasonal flu, may include fever, headache, coughing, sneezing, sore throat, and muscle or joint pains, which can last up to a week. A significant number of people who have been infected with the virus have also reported diarrhea and vomiting. Antiviral drugs such as Tamiflu and Relenza have been found effective at treating and reducing the duration of the illness, usually by a day or two. But in order to be most useful, they must be administered within 12 to 48 hours of symptoms onset. That could be a problem considering that identifying the virus by traditional cell culture can take days, and the rapid detection tests that can provide results in 30 minutes or less fail to identify H1N1 more than half the time, according to a new government report.

The Centers for Disease Control (CDC) studied tests using clinical specimens that had been shown to contain an influenza virus through laboratory testing from three companies: Binax Inc., Becton, Dickinson & Co., and Quidel Corp. Of the three, the Quidel test fared the best, detecting 69 percent of the infections. The Becton, Dickinson test detected 49 percent and the Binax test detected 40 percent. All tests detected seasonal flu better than the H1N1 virus. “These findings indicate that, although a positive (rapid detection test) result can be used in making treatment decisions, a negative result does not rule out infection with novel influenza A (H1N1) virus,” the authors wrote.

These findings are not entirely unexpected. A recent study in the Journal of Clinical Virology found that one test detected only 10 percent of H1N1 infections, and a second detected only 40 percent. The rapid tests “are missing a ton of flu” that could be picked up by a more sophisticated laboratory culture, said Christine C. Ginocchio, director of the division of microbiology, virology and molecular diagnostics at the North Shore-Long Island Jewish Health System in Lake Success, N.Y. And in a letter to the New England Journal of Medicine in June, Navy researchers described the poor sensitivity of the Quidel tests, pointing out that they detected only half of the infections picked up by a more sensitive technique.

However, the manufacturers of the tests argue that their products are helpful if used appropriately. Senior vice president for clinical and regulatory affairs at Quidel Corporation, John D. Tamerius, says that Quidel’s QuickVue flu test for the detection of Influenza Virus type A and type B antigens could detect 80 percent of infections if done directly from a self administered nasal specimen swab taken correctly and if the test was given early in the course of the disease, when more virus was present. “When these tests are used properly, the performance is very, very good,” Tamerius said.

Last week the CDC updated guidance urging caution in relying on the tests, fearing that the negative readings might prevent health care providers from treating patients with antiviral drugs, particularly those at high risk, such as pregnant women and those with asthma or other underlying medical conditions like heart disease and diabetes.

Resources: http://www.healthnews.com/alerts-outbreaks/rapid-tests-detecting-h1n1-flu-not-reliable-3543.html

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