Feb 6, 2013 (CIDRAP News) – The authors of a new review say there is little evidence of unrecognized human cases of H5N1 avian influenza, but the studies done so far have too many limitations to settle the controversial question.
Researchers from the Center for Biosecurity at the University of Pittsburgh Medical Center reviewed 29 serologic studies and found only four that identified anyone carrying antibodies to currently circulating H5N1 strains. But many of the studies reviewed had methodologic problems, such as lacking a comparison group with no exposure to the virus.
The authors say their findings suggest that mild or asymptomatic cases H5N1 cases are probably few, but the studies done so far are not capable of determining "the true prevalence or severity of H5N1 infections." Their findings were published online yesterday in Clinical Infectious Diseases.
The debate over the existence of mild or asymptomatic H5N1 cases has continued for years and was renewed last year amid the controversy over experiments in which lab-modified H5N1 viruses were found to have airborne transmissibility in ferrets.
The question centers on whether H5N1 is really as dangerous as it appears from the 59% case-fatality rate (CFR) in confirmed human cases recognized by the World Health Organization (WHO).