There is no evidence that anybody has been infected by a potentially lethal influenza test sample sent to thousands of laboratories worldwide, but laboratory personnel who worked with the samples should be closely monitored for flu symptoms, the Centers for Disease Control and Prevention said Wednesday.
Dr. Julie L. Gerberding, head of the CDC, said at a news conference that there was no record of anybody being infected by a sample from any such test, which was used to ensure that laboratories correctly identify viruses.
Even so, the CDC has recommended that any laboratory workers showing symptoms should be immediately tested for the H2N2 Asian flu virus, which was responsible for the 1957 pandemic that killed at least 1 million people worldwide.
Since September, the virus sample has been sent to 5,000 laboratories -- most of them in the U.S. -- as part of routine testing to ensure that workers were proficient at identifying various pathogens. The tests normally use flu samples from strains that are now circulating and pose little serious threat.
But the company that produced the test samples, Meridian Bioscience Inc. of Newton, Ohio, included the deadly virus, which has not infected a human since 1968.
The CDC said the virus never should have been sent in the test kits -- though its own rules did not prevent it. Meridian did not return calls seeking comment.
Several virologists said that anybody born before 1968 would have some immunity to the virus. Those born later could be susceptible to infection. But the chances of the virus escaping from a controlled laboratory environment are extremely slim, the scientists said.
Jan de Jong, an influenza expert at Erasmus University in Rotterdam, the Netherlands, said labs were used to dealing with such exotic microbes and were set up to avoid inadvertent releases. "We have this virus in our refrigerator," he said.
Still, he said it was worrisome that the laboratories that received the kits had no way of knowing they were working with a dangerous strain.
The CDC was in the process of upgrading guidelines for handling H2N2 to require extra safety precautions, which are already standard in other countries.
Dr. Jared Schwartz, an officer at the College of American Pathologists, one of several groups that organizes the tests, said Meridian workers apparently thought the virus, selected from the company's stocks, was a typical strain.
The college was never told that it was H2N2, Schwartz said at a news conference.
For months, the sample's full identity went unnoticed. The proficiency tests require laboratories only to detect the presence of a flu virus and identify it as type A or B.
Last month, a hospital laboratory in British Columbia was analyzing a specimen taken from a patient and detected the presence of an influenza strain, Dr. David Butler-Jones, Canada's chief public health officer, said at a news conference.
The specimen was sent to the National Microbiology Laboratory in Winnipeg, which identified the sample as H2N2.
Later investigation showed that the patient did not have any strain of the flu. The proficiency test sample had been next to the patient specimen and contaminated it, Butler-Jones said. Such cross-contamination, though rare, is caused by lab worker error, virologists said.
The CDC and the World Health Organization have put out a call to destroy the test kits.
The task is easily accomplished with an autoclave, a sort of pressure cooker used in laboratories, said Dr. Peter A. Gross, an influenza expert at Hackensack University Medical Center in New Jersey.