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H5N1 Bird Flu Sample Collection Problems in Indonesia
October 4, 2005
"Although the local test shows that he is positive, we don't want to reach any conclusion yet as we are awaiting results from Hong Kong," Kandun told Reuters.
Common symptoms of the disease, such as pneumonia, can have other causes, while local testing has not always squared with results from the Hong Kong laboratory recognised by the World Health Organisation (WHO).
The above comments on test results is only partially true. Each sample that is PCR positive in Jakarta has also been PCR positive in Hong Kong. The discrepancy is with the HI test, which can be positive while the PCR test is negative. These are the samples that are PCR negative in Hong Kong, but they are also PCR negative in Jakarta.
The discrepancies are really linked to sample collection. PCR tests of nasal and throat swabs are only positive for limited times. Samples collect too early, as well as those collected after the H5N1 has moved to the lungs, will be negative. However serum samples from these patients will frequently be antibody positive.
The problem is increased by the sample collection procedures in Indonesia, which rely on collection at the referral hospital. By the time the patient is transferred, especially for milder cases with a lower viral load, H5N1 will be cleared from the nose and throat prior to sample collection.
Collection of samples at the primary facility, as well as the referral facility, will lessen the chances of false negatives in nose and throat swabs.
The current protols will easily miss mild cases of H5N1.