Sept. 14 (Bloomberg) -- After being infected with swine flu, Brent Robb, a 34-year-old New Zealander with no pre-existing medical conditions, spent 11 days in a coma induced by doctors in a last-ditch effort to save his life.

A printer who liked to bike 12 miles a week for exercise, Robb lost two months of work while sick, and a sixth of his body weight. He survives as an example of a mystery hovering over the fast-moving pandemic that has spread to 177 countries in four months, yet causes little more than a fever and a cough in all but a select few.

Seasonal flu kills predominantly the frail elderly. Researchers are trying to determine why the H1N1 swine flu virus, much like the Spanish Flu of 1918, is lethal to a portion of young people in good health. The reason may involve a person’s genetics, or simply taking a deep breath just as a nearby infected person sneezes.

“That’s a question we have to find the answer to,” said Nikki Shindo, a Geneva-based doctor leading the World Health Organization’s investigation of swine flu patients.

Underlying conditions that can intensify the effects of flu include respiratory illnesses, especially asthma, cardiovascular disease, diabetes, a suppressed immune system, and even pregnancy. About 25 percent to 50 percent of severe cases worldwide involve healthy young and middle-aged people like Robb, according to WHO Director-General Margaret Chan.

Unpredictable Disease

It is a statistic that highlights how unpredictable the disease has turned out to be, said Ian Barr, deputy director of the WHO’s Collaborating Center for Influenza in Melbourne.

“People are happy to dismiss serious cases among people with underlying conditions,” Barr said in an interview. “It’s a wake-up call when healthy people are struck down.”

As many as 2 billion people, or 30 percent of the world’s population, may become infected by the new virus as it spreads globally, according to the WHO. Identifying those likely to recover without medical help and those who may become severely ill will help prioritize vaccination and drug treatment.

In Australia, the median age of people dying from seasonal flu is 83. With the H1N1 swine flu, it is 54 years, according to the government’s Aug. 28 influenza surveillance summary report. In New South Wales, Australia’s most-populous state, the majority of H1N1 patients in intensive-care units are 30 to 59 years old, the state government’s Sept. 9 weekly report notes.

Spanish Flu

A similar trend has been observed worldwide since the pandemic was discovered in April in Mexico. There, 70 percent of fatal cases were of people ages 20 to 59 years, Guillermo Ruiz- Palacios, head of infectious diseases at the National Institute of Medical Sciences and Nutrition in Mexico City, told global health experts today at the Interscience Conference on Antimicrobial Agents and Chemotherapy in San Francisco.

Original Article, here.