NEW YORK (Reuters) -- After two years of mild flu seasons in the United States, the deaths of five children in Colorado have officials bracing for a harsh flu season that could lead to higher hospital admissions.

"We're getting ready for it to be a severe season, but we don't know how severe it could be," said Jennifer Wright, an epidemiologist at the Centers for Disease Control.

Wright declined to project specifically how bad this year's flu season will be, but Dr. Gregory Schwitzer, vice president of clinical programs for Intermountain Health Care, said it is a "major epidemic" in the Salt Lake City area.

Dr. William Schaffner, chairman of the department of preventive medicine at the Vanderbilt Medical School in Nashville, said the flu virus has spread very early in the season.

"That is always the harbinger of a bad season," Schaffner said.

The flu season's peak occurs any time from late December through March in the United States, with about 10 to 20 percent of U.S. residents getting the flu. During an average flu season, about 114,000 persons are hospitalized and 36,000 die from flu-related problems, the U.S. Centers for Disease Control said.

The current strain of influenza, Fujian A, is an H3 virus, a category that is more virulent than normal.

Some publicly traded hospital chains, such as HCA Inc., reported weak admissions during the first quarter of 2003, citing a mild flu season last time around. HCA, the largest U.S. hospital chain, declined to comment about the impact of the flu upon admissions for this season, because of the unpredictability of flu patterns.

A Centers for Disease Control map said influenza is widespread in 10 states and there were regional outbreaks of flu in an additional nine states during the week ended Nov. 22. The Western states have been affected the most so far.

"ERs have been pretty busy with people taking their children there," said Lori Maldonado, a spokeswoman for the Colorado Department of Public Health and Environment. The agency is urging concerned parents to contact their doctors before coming to the hospital.

Schwitzer said Intermountain Health Care, a health system with 20 hospitals and about 100 clinics in Utah and a hospital in Idaho, said the system has had 800 to 1,000 confirmed cases of flu, which is unusual for this early in the season.

Most flu seasons peak in January or February, Schwitzer said.

Health officials are encouraging people to get a flu shot. Although the vaccine does not directly target the Fujian A strain, the vaccine mitigates flu symptoms, officials said.

Schwitzer said antiviral drugs, such as Tamiflu or amantadine, are most effective in diminishing symptoms when they are administered during the earliest stages of the flu.