The H7N9 virus is disproportionately affecting older men as it spreads in China, the World Health Organization said in a bulletin on Monday, for reasons that are not immediately clear.

Between March 31 and April 16, when the WHO researchers were crunching the numbers, there were 63 reported cases of the new bird flu strain, with a median age of 64 years and with men making up 71% of cases. Although the 22% fatality rate in all males was similar to females, the rate of deaths in older men was 20%, compared to no deaths in older females.

That demographic breakdown, while based on an early assessment with a small sample size, stands in contrast to the previous H5N1 influenza outbreak in China, in which most patients were working-age adults, with no disparity in gender. China as a whole has a mostly working-age population, and elderly women outnumber elderly men.

The researchers said the answer could lie in different levels of exposure due to “gender-associated practices and norms,” differences in the way men and women of different ages respond to the virus, or different health-care seeking behaviors, leading to a bias in the way the cases have been reported.

The H7N9 toll as of Monday stands at 102 cases and 20 deaths, and the outbreak has begun to take a toll on industry and tourism.

Local media reports that some duck restaurants have seen a drop in business of at least 15 per cent and shares in related businesses have fallen in value. Chicken restaurant giant KFC has experienced a “significant negative impact” on sales, despite the Beijing World Health Organization chief joking that he “eat[s] chicken every day”.

Bloomberg reports that Chinese imports of soybeans are likely to fall 2 percent to 58 million tons this year, breaking an eight-year string of increases in the animal feed, as consumers shy away from pork and poultry. Imports also plunged in 2003-2004 and 2006 during previous viral outbreaks. Spring Airlines, among other carriers, has stopped serving chicken and duck in their in-flight meals and some schools in Shanghai have changed their menus.

Meanwhile, new research by Beijing-based Hong Yuan Securities predicts that eastern China’s tourist spots will be affected by the H7N9 outbreak, particularly during the May Day holiday. Tour company shares have reacted accordingly and analysts have warned of bigger effects to come if human-to-human transmission is confirmed.

Additional reporting by Jake Maxwell Watts