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False H5N1 Negatives in Pakistan and the United States?
December 17, 2007
The Health Ministry said it was treating people who had been in contact with those infected, setting up isolation wards and procuring drugs for treatment and protective clothing for health workers.
The above update raises additional questions regarding the spread of H5N1 in Pakistan and the United States. Testing of samples collected after the start of Tamiflu treatment can generate false negatives, since Tamiflu reduces v\ral load, which is the target of PCR testing. Earlier reports indicated several H5N1 patients had mild symptoms or were asymptomatic, but registered positive on a "less reliable" test, which was likely to be an H5 antibody test. This testing may be more reliable than PCR testing for patients who have already started Tamiflu treatment. Ideally, samples would be collected before or at the start of Tamiflu treatment.
The above information raises questions about the brother (38M) who returned to the US after attending funeral(s) of his two brothers in Pakistan (see Nassua County report). Since the dates of death were ten days apart (November 19 and 29), there would be significant exposure opportunities if the visiting brother was in Pakistan for both funerals.
The Nassua report indicates the patient was prescribed Tamiflu also, but it is unclear if specimens were collected before or after the start of treatment (which may have begun in Pakistan).
More information on the testing, including follow-up tests on convalescent, serum would be useful.
Recombinomics Paper at Nature Precedings