The risk of bird flu mutating into an form more easily spread between people is still high and there could be an upswing in human infections at the end of the year, the World Health Organization (WHO) warned on Friday.
In a report analyzing more than 200 known bird flu cases, the United Nations agency identified three peaks in human infections since 2003, all concentrated during the winter and spring seasons in the northern hemisphere.
“If this pattern continues, an upsurge in cases could be anticipated starting in late 2006 or early 2007,” the WHO said, adding that further analysis was needed.
“Moreover, the widespread distribution of the H5N1 virus in poultry and the continued exposure of humans suggest that the risk of virus evolving into a more transmissible agent in humans remains high,” it said.
While it remains mostly a disease of birds, experts fear the avian influenza virus could mutate into a more transmissible form and spark a pandemic killing millions of people.
The WHO study of human cases of H5N1 between December 2003 and April 2006 — during which 203 people caught the disease, causing 113 deaths — concluded that children and young adults were most vulnerable to dying after exposure to the strain.
It said the pattern of infections was “reminiscent” of that seen during the 1918-1919 Spanish flu pandemic which killed 40 million to 50 million people worldwide.
Confirmed human cases in the recent bird flu outbreak ranged in age from three months to 75 years.
But the highest proportion of bird flu cases occurred among those aged 10 to 29, with the typical victim being hospitalized four days after falling ill, the WHO said.
Some 56 percent of patients died five days later -- nine days after onset of symptoms, according to the study. People aged 50 and older had the lowest fatality rate.
“The differences in the age-related case-fatality distribution among H5N1 cases are reminiscent of those observed during previous influenza pandemics, particularly in 1918, where case-fatality rates were higher among young adults,” it said.
Sharing such data could be a useful part of an “early warning system that will collectively defend all countries against a common threat,” it added.
Standardizing collection of epidemiological and clinical data should help improve experts’ ability to detect exposure patterns and identify risk groups, it said. This in turn would help researchers to adapt and target preventive measures.