re: pandemic may cost up to two trillion world ban 03 July...

re: pandemic may cost up to two trillion world ban 03 July 2006

Human Avian Influenza Follows Seasonal Patterns, U.N. Finds
New study suggests Northern Hemisphere winter could bring more cases



By Charlene Porter
Washington File Staff Writer



Washington – A new study of the incidence of avian influenza in humans suggests that the disease follows the same patterns as seasonal human influenza with an increase in cases during the winter months of the Northern Hemisphere.

That tentative conclusion was issued in the Weekly Epidemiological Record (WER), published June 30 by the World Health Organization (WHO). The study also suggested “an upsurge in cases could be anticipated starting in late 2006 or early 2007.”

In addition, researchers are cautious in qualifying their analysis of the 203 human cases studied, noting those cases represent only those confirmed and reconfirmed in laboratories with samples provided only by patients who presented symptoms of illness. There is no way of knowing, the WER said, whether these cases accurately represent all human cases of infection.

“Some patients may have died before being tested or diagnosed, mildly symptomatic people may not have sought medical care, and false-positive or false-negative test results may have occurred,” according to the article, which recommended further studies of at-risk populations.

This epidemiological study focused on human cases of highly pathogenic avian influenza that occurred between December 2003 and April 2006. Other human cases caused by the dangerous H5N1 viral strain have been confirmed through May and June, bringing the current tally of human cases to 228, resulting in 130 deaths.

Humans have virtually no immunity to this viral strain, which appeared only in animals prior to 1997. So far, most infections have occurred after a person has had direct contact with diseased birds or their environment, with minimal transmission occurring from human-to-human. If the virus mutates to become contagious among people, international health officials warn that it could trigger a pandemic influenza with the possibility of millions of deaths and widespread social and economic consequences.

The analysis found that the mortality rate in the cases studied was 56 percent overall, but different patterns emerged when the cases were examined by age group. Young people are more likely to die from H5N1 infection, according to the findings, with a 73 percent fatality rate among those 10 years to 19 years of age. The lowest rate of death – 18 percent -- came in those over 50.

A similar pattern emerged in analysis of the patterns of infection. The median age of confirmed cases was 20 years, and 90 percent of cases occurred among people younger than 40. This finding contrasts with the predictable patterns of seasonal influenza, which takes its highest toll among elderly people.

The vulnerability of younger people has been noted over the months as human infections have grown. The pattern is consistent with the demographic patterns of the Spanish Flu epidemic of the early 20th century in which young adults disproportionately were affected.

The article cautions against inferring a link between age and disease exposure. The cases are occurring in countries where the average age of the populations is low, with a large proportion under 15. Therefore, the occurrence of the disease in the young might say more about population demographics than about the characteristics of the disease.

The activities of the young previously have been cited as a possible explanation for their apparent vulnerability to infection. Children play in yards where chickens are kept, and children often are assigned the role of catching, killing or defeathering the chickens as they are prepared for a family meal.

The contrast between the demographic patterns seen in H5N1 infection and those seen in seasonal influenza has been noted before and is echoed in this latest analysis. It is another aspect of the disease that demands further study.

The disease’s appearance in growing numbers of countries in 2006, increasing the opportunity for human exposure, suggests “that the risk of virus evolving into a more transmissible agent in humans remains high,” according to the report.

The full text of the article is available on the WHO Web site.