WHO Requests Additional Samples from Karachi Cullers
Recombinomics Commentary 07:51
February 5, 2008
A joint team of national and international health agencies has taken some more samples from three suspected patients, who were shifted from the bird flu-infected poultry farm in Gadap to the Civil Hospital Karachi on Friday.
Sindh Deputy Secretary Health Dr Shakeel Mullick, who is also the focal person on bird flu in humans, on Monday night said that throat, nasal and blood samples were taken in the presence of a committee comprising representatives of the World Health Organisation, the National Institute of Health, Islamabad, and the federal and provincial health ministries. They had been sent to the NIH laboratory in Islamabad and the result was expected after 72 hours, he added.
CHK Medical Superintendent Dr Kaleem Butt said that the team took fresh samples as those taken earlier were not helpful for the NIH laboratory tests.
The above comments describe requests for new sample collections from the three patients in isolation from the first cull near Karachi. PCR and viral sequencing and isolation tests use throat and nasal swabs, which were not likely taken earlier. Blood samples can detect a rise in antibodies, but the rise is optimal on samples collected weeks after onset dates. Thus, paired serum samples can be used to detect H5N1 infections, but early results and viral isolation require swab collections.
The lack of swab collections, as revealed above, is even more glaring in India and Bangladesh. Neither country has ever reported a human H5N1 case, and the failures to detect cases may be related to testing procedures.
Although swabs require collections at the appropriate time, media reports of sample collections in India and Bangladesh fail to mention the collection of nasal and throat swabs. These efforts do not guarantee positives in H5N1 infected patients. In Turkey, throat swabs from the four siblings were negative, although three died. The fatal cases were positive when fluid from the lungs was tested. Thus, the nasal and throat swabs may also generate false negatives, especially if collected too early or after the start of Tamiflu treatment.
Although false negatives are common, limiting testing to initial serum collections, virtually assures a negative result.
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