One of the great debated points about human H5N1 infections is whether it is always severe, or whether we only detect the `sickest of the sick', and that there are thousands of unnoticed infections out there.
There are vocal critics who have lambasted the WHO, and anyone else quoting the 60% case fatality rate, maintaining that they totally ignore these thousands of cases that have gone `undetected'.
Many of these critics hang their hat on a study done in Vietnam, based on a questionnaire (not medical exams or blood studies) that suggested that mild H5N1 infections were common. This study, by Anna Thorson, M.D., Ph.D., from the Karolinska Institute, has not been widely accepted due the lack of diagnostic testing.
Today at the Options For Influenza Control VI Conference in Toronto another piece of evidence was produced that further diminishes the idea that there are many mild cases of H5N1 out there.
A seroprevalence study of more than 900 people who were presumably exposed to the virus showed no serological evidence that they had been infected and fought off the disease.
In a classic good-news/bad-news format, this means that so far, the H5N1 virus has been exceedingly difficult to catch, but is devastating once it is contracted. This study reaffirms what other smaller studies in Hong Kong, China, and Cambodia have suggested in the past.
This from Medpage Today
By Michael Smith, Senior Staff Writer, MedPage Today
Reviewed by Zalman S. Agus, MD; Emeritus Professor at the University of Pennsylvania School of Medicine.
June 19, 2007
TORONTO, June 18 -- Highly pathogenic avian flu is rarely transmitted to people and apparently never in a mild or asymptomatic form, a Thai researcher said here.
A study of 901 people who lived near confirmed victims of the H5N1 avian flu strain showed no serological evidence that they had been infected and fought off the disease, Rapeepan Dejpichai, M.D., of the Thai Ministry of Health told attendees at the Options for Influenza Control meeting.
Even those who were in close contact with both infected birds and infected people showed no sign of ever having been infected, Dr. Dejpichai and colleagues found.
The study is consistent with findings in Hong Kong, China, and Cambodia, which showed viral seroprevalence of no more than 10% among poultry workers and people living in villages where H5N1 outbreaks occurred, she said.
But it contradicts a population-based study in Vietnam, published last year, that concluded that mild cases of the virus were likely to be common. (see Mild Avian Flu Transmission May Be Common)