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Bird flu most deadly in teens, young adults: WHO
Updated Fri. Jun. 30 2006 8:49 AM ET

Canadian Press

The H5N1 avian flu virus has exacted an alarmingly high death toll
among adolescents and young adults -- an eerie echo of the infamous
Spanish flu, a new analysis of cumulative cases by the World Health
Organization confirms.

"The differences in the age-related case-fatality distribution among
H5N1 cases are reminiscent of those observed during previous pandemics,
particularly in 1918, where case-fatality rates were higher among young
adults," the review said.

The report, published Friday in the WHO's publication the Weekly
Epidemiolgical Record, also urges countries to share data on avian flu
cases, saying doing so "will collectively defend all countries against
a common threat.''

One of very few reviews drawing together details of accumulated H5N1
cases, the report looked at the trends evident in the 203 confirmed
cases in nine countries that occurred between December 2003 and the end
of April 2006. Of that number, 113 people or 56 per cent died.

A number of infections have occurred since, bringing the global total
to 228 cases and 130 deaths in 10 countries.

The age group with the highest fatality rate was 10-to-19-years olds;
73 per cent of cases in that age range who contracted the virus died
from it, noted the authors. (As is the practice of the Weekly
Epidemiological Record, authors are not listed by name.)

Sixty-two per cent of 20-to-29-year olds and 61 per cent of
30-to-39-year olds who tested positive for the virus succumbed to the
infection, said the report.

By age 50 and older, the fatality rate dropped to 18 per cent, though
the overall number of infections in older adults is low in comparison
with younger age groups. In the very young -- under age five, and five
to nine years of age -- the fatality rates were 43 per cent and 41 per
cent respectively.

Adolescents and young adults weren't just more likely to die from the
virus; they were also more likely to become infected in the first
place, the review confirmed. The highest proportion of cases occurred
in people aged 10 to 29 years.

In part, that might relate to the fact that many of the countries which
have seen human cases have young populations, the authors said.

Exposure patterns in adolescents and young adults could also help
explain the spike in infections in those aged 10 to 29, the report
said, noting that young girls and women might be more at risk because
they are often involved in culling, defeathering and preparing chickens
for consumption. There were slightly more female cases than male, 106
to 97.

The report cautioned against drawing too many conclusions on spotty
evidence.

"The incomplete nature of the data on exposure make it difficult to
infer a link between age and exposure, and further studies are needed,
especially to assess whether younger people or other groups (such as
pregnant women) have an increased risk of contracting the infection,"
the report said.

British influenza expert Dr. Angus Nicoll recently bemoaned the lack of
detailed data on the human cases and disease outbreaks, calling it "a
collective failure ... that must be overcome."

Nicoll, who co-ordinates influenza activities at the European Centre
for Disease Prevention and Control in Stockholm, complained that the
number of analytical reports of outbreaks is "embarrassingly small."

"Consequently little more is known now than in 1997 about an infection
that seemingly remains hard for humans to acquire, but is highly lethal
when they do," he wrote in an editorial in the May issue of
Eurosurveillance, an online publication on European communicable
disease surveillance and control.

The lack of good follow-up studies after outbreaks are contained means
the world still isn't clear if some people are getting the disease but
only experiencing mild or virtually no symptoms, for instance.
Asymptomatic infections, as they are called, occur with many infectious
diseases, though not all.

This piece of information is crucial as it would indicate whether
calculating the fatality rate based on recorded cases overestimates the
lethality of the disease.

If studies testing the blood of exposed people showed many had
antibodies to the virus -- signalling they had been infected and
survived -- it would be proof the fatality rate was actually much
lower.

Few such studies have been done and fewer still have been published in
the scientific literature. Those that are in the public domain suggest
mild, missed cases are not occurring.

The many knowledge gaps about H5N1 and its infection and fatality
pattern highlight the need for countries which have human cases to
share information with the global community, the report said.