Many observers have speculated such. Little hard evidence has been presented that this is the case. If you are in possession of the smoking gun I know numerous immunologists, epidemiologists, and virologists would love to see it. The point you, and apparently he, are missing, is that widespread human infections would be a bad thing, even mild ones, as many additional opportunities for recombination and, especially, reassortment would occur.
It appears that this Ed Kilbourne has his posterior glued to his rocking chair and doesn't venture out in the field much these days. A brief Goggle on his name and H5N1 will show that many have already dismissed his comments, such as this poster:
It seems to me that Dr. Kilbourne makes several statements based on old paradigms. Yet a lot of the public are going to accord him expert status on the basis of being an emeritus professor.
Would you be included in that group?
In light of the fact that no seroprevalence studies have been published, a study was recently completed and published in Archives of Internal Medicine that supports the "more widespread and mild symptom theory".
http://archinte.ama-assn.org/cgi/content/abstract/166/1/119
Additionally, commentary from Dr. Henry Niman (Dr. Doomsayer some say) last June that suggests the same:
“Although the positive western blot data has not been confirmed, positive data would be consistent with more clusters in the north which are large and extend over a longer time period. The alarming increase in admission is further cause for concern because the admitted cases have mild disease, suggesting an even larger number of unreported cases with slightly milder disease.
This H5N1 is silently spreading mild disease in human and asymptomatic infections in poultry, which would move the pandemic to phase 6. The seeding of the human population with H5N1 sets the stage for further recombination in the fall when migratory birds bring in new sequences, which will cause new problems.”
http://www.recombinomics.com/News/06260502/H5N1_Silent_Spread_Vietnam.html
If you want me to dig a bit deeper and find more for you, let me know.