The current outbreak of A/H1N1 flu virus, previously known as swine flu, is likely to return to the United States after subsiding during the summer months, the Health Day News reported on Wednesday.

That return could come with a vengeance, or not, the report quoted experts as saying.

So far, some of the most affected nations have been in North America and Europe, but the flu, like the regular seasonal flu, is spreading more easily in the winter, the report said.

In North America, the summer should slow down the spread of H1N1 flu, neither viruses nor bacteria survive well at temperatures above 70 degrees Fahrenheit, according to experts.

"We can't actually be certain, but there likely will be a reemergence," Len Horovitz, a pulmonary specialist with Lenox Hill Hospital in New York City, said. "We're seeing this virus at a time that is usually the end of the flu season, so you would expect, because the flu virus is hardier in cold weather, that there will probably be a return."

Taking into consideration of previous flu pandemics, the pattern has always been a mild epidemic in the early summer or late spring, then it will become a larger epidemic in the winter, Luis Z. Ostrosky, an associate professor of medicine and epidemiology in the division of infectious diseases at the University of Texas Medical School in Houston, said. "If this were to follow the pattern of previous outbreaks, we would see it again in the winter."

Ostrosky was referring to 1918 Spanish flu pandemic, 1957 Asianflu and 1968 Hong Kong flu.

This pattern of an initial "herald wave" followed by a second wave is common in the flu world, the report said, adding: How and when the flu spreads is dependent on other factors as well: the fitness and efficiency of the virus itself along with its innate ability to replicate; the susceptibility of the host; and the environment, which includes not only the weather, but also human behavior, for example, groups of people confined together inside, making it easier for the virus to jump from person to person.

Experts fear public health systems could be overwhelmed if H1N1flu and regular flu collide in major urban populations.

(Xinhua News Agency May 7, 2009)