SOME Australians may have been falsely diagnosed with human swine flu while others with the disease may have been sent home with a negative result because the laboratory test used to identify the potentially deadly virus is only about 90 per cent accurate.
So far more than 1200 Australians have tested positive to swine flu.
NSW Health is among those using polymerase chain reaction testing, also known as the PCR testing, to identify the H1N1 strain of influenza. Last night NSW Health declined to make any further comment.
The latest information from the World Health Organisation, supported by the US Food and Drug Administration, suggests the newly developed rRT-PCR "rapid" testing method gives only a "presumptive positive" rather than a "definitive positive" result for H1N1 influenza. According to reports from both organisations, the test can also provide a "false negative" result in cases where the patient actually has the virus. PCR testing is the global benchmark used to identify viruses and is endorsed by the WHO.
In April, the FDA issued an emergency use authorisation to allow a "rapid" form of the method to be rushed to laboratories across the US to combat a potential swine flu epidemic, even though the method had not been fully developed or obtained approval. A document released by the FDA on April 28 states only that rRT-PCR swine flu testing "may be effective" in testing for swine flu. The FDA report states that "a positive result indicates that the patient is presumptively infected with swine flu virus, but not the stage of infection", and that "a negative result does not, by itself, exclude the possibility of swine flu virus infection".
The WHO has issued its protocols for using the new test method to laboratories around the world. That document states tests can provide only a "presumptive positive" result for swine flu. The WHO document also said "a false negative result may occur if inadequate numbers of organisms are present in the specimen due to improper collection, transport or handling".
The rRT-PCR testing method was developed by the global pharmaceutical giant Roche - the company that also owns the rights to Tamiflu, one of just two anti-viral drugs used to treat the virus. George Koumantakis, the Scientific and Regulatory Affairs manager for Roche Diagnostics Australia, said the PCR testing method was "about 90 per cent accurate".
"It's impossible to claim 100 per cent accuracy for the method due to a number of reasons," Dr Koumantakis said. "The primary one is that the virus only has to mutate slightly for the test to be completely ineffective."
Last week Roche reported that stocks of Tamiflu had sold out in Australia due to unprecedented demand.
The number of Australians with the H1N1 virus increased from 1207 to 1224 yesterday. The Health Minister, Nicola Roxon, said the virus was mild in Australia, and only about 10 people had been hospitalised. (Sydney Morning Herald)
