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Serious H5N1 Bird Flu Surveillance Flaws
May 5, 2006
``The peak transmission either in poultry or to humans is in the winter months,'' said Robert Webster, the Rosemary Thomas professor at St. Jude Children's Research Hospital in Memphis, Tennessee.
The above comments on avian influenza infections raise serious questions about the surveillance of H5N1 bird flu worldwide. The data from Britain is particularly striking because the detail indicate testing was throughout the peak period in the fall and winter, yet virtually no avian influenza was found in dead or living wild birds.
Avian influenza in birds is common. Testing in Canada of young mallards in August, 2005 found low pathogenic H5 throughout southern Canada. H5 was detected in 24% of the birds tested in British Columbia and as many as 50% of the tested birds had some strain of avian influenza.
Test results from Britain indicate samples were collected throughout the winter months. Only two positives were obtained from live birds, although over 3000 birds were screened. Attempts to isolate virus from the two positives failed.
In dead birds, there was one positive, H5N1, in a whooper swan in Scotland. Again over 3000 dead birds were tested.
Positive data on 3 birds out of 7000 indicates the surveillance methodology was seriously flawed. These flaws were further supported by the H7N3 outbreak in at least farms near Norwich. No H7 was detected in the surveillance samples, again highlight a high rate of false negatives.
Collection and storage flaws may have contibuted to the false negatives reported by DEFRA. However, false nagatives can be generated at many points in the collection and storage process. Countries reporting no positievs in thousands of samples have serious issues.
Many countries in Europe detected H5N1, indicating H5N1 had migrated into the region in the fall of 2005. As indicated by the positive whooper swan in Scotland, H5N1 was in long range migratory birds and therefore would have spread widely throughout the area. However, many European countries still claim no H5N1 infections. No country, other than Russia has detected H5N1 in live wild birds.
These data further demonstrate that the enhanced surveillance in Europe and throughout the world is seriously flawed. The reports of false negatives do little to blunt the spread of H5N1. Countries testing thousands of birds and finding no avian influenza have a serious sensitivity and selection problem.
Issues of false negatives in H5N1 have been obvious since early 2004. The failure to adequately address the failed surveillance remains scandalous.