Three more children have died from complications of the flu in Colorado, bringing the state's death toll to at least four in a season that has hit early and hard.

Joseph Williams, 8, of Wellington, died Monday. On Tuesday, Children's Hospital reported the deaths of a 2-year-old and a 21-month-old. A 15-year-old girl died at Children's last week.

The 15-year-old and the 2-year-old had medical conditions that made flu especially dangerous to them, health officials said. Joseph and the other child had been healthy.

Larimer County officials reported the death of an 8-year-old but did not identify the child.

Joseph's family held a news conference Tuesday night to urge parents to take their children to the doctor at the slightest sign of trouble.

"If your kids even act sick, take them in and get them checked out," said the boy's father, Scott Williams. "If this saves even one life, there's meaning to it."

Children's did not identify its patients.

As of Tuesday, there were 3,399 confirmed flu cases in Colorado. The total for all of last year's flu season was 2,681.

Colorado had 19 flu-related and 729 pneumonia-related deaths last year among people of all ages, according to health officials. Pneumonia is a frequent complication of the flu.

The state's chief medical officer said this flu season is earlier and worse than usual.

"Young physicians in emergency departments are saying they've never seen a flu season this bad. Others are saying they have not seen it this bad in 20 years," said Dr. Ned Calonge of the state health department.

Adding to the problem is the fact that this year's vaccine does not protect against the so-called Fujian strain from Australia, which is causing some of the most severe illness elsewhere and is believed to be in Colorado.

Calonge said he did not know whether the children who died had been vaccinated. Joseph's parents said he had not had a flu shot.

Nationwide, about 36,000 people die from flu complications each year. But, experts say, the vast majority of deaths are among the elderly and those whose immune systems are compromised. Healthy children rarely die from the flu.

"We had child deaths last year, but not this many and not this close together," Calonge said.

At Children's Hospital, where three of the four children died, more than 700 kids have tested positive for flu, and scores have been hospitalized, said Dr. Chris Nyquist, the hospital's medical director for infection control.

Once they have several confirmed cases, doctors at Children's and elsewhere stop performing tests on every patient with flu symptoms.

That makes officials certain that the real number of people suffering from the flu is much higher than the number of confirmed cases.

In Joseph's case, flu struck quickly.

The third-grader was in class at Eyestone Elementary School on Friday and showed no signs of illness, principal John Karbula said.

Monday, Karbula told Joseph's classmates he had died.

"It is an extremely tragic circumstance," Karbula said. "Our thoughts, our prayers and our love go out to the family. I know the entire community feels that way."

Tuesday, the school sent a letter home to parents, telling them of Joseph's death.

"Larimer County health officials have asked us to inform parents that normal flu symptoms, while always serious, are typically not life-threatening. However, if your child shows flu symptoms and signs of respiratory distress, you are advised to take them to the emergency room as quickly as possible," the letter said. "Should you have any questions or concerns about flu symptoms in your child, please contact your family physician."

Health officials are baffled by the boy's death: Healthy children virtually always get better, Eyestone Elementary doesn't have a severe flu outbreak, and Joseph complained of stomach pains and nausea rather than the muscle aches and difficulty breathing more typical of flu.

Flu season normally runs from November to May. Last year, there was one reported case by Nov. 15.

No adults have died of flu so far this season, but plenty have turned up in emergency rooms across the metro area.

"Are we seeing flu? Yes, yes and yes," said Dr. David Steedle, medical director of Swedish Medical Center's emergency department.

The hospital has stopped testing every suspected flu victim, but since about the second week of the month, the number of patients coming through the emergency department has gone up about 20 percent, "and it's just due to influenza," Steedle said.

Emergency room staff at St. Anthony Central and St. Anthony North hospitals are seeing 50 to 60 flu patients a day, spokesman Scott Chase said.

It's not too late for Coloradans to get flu shots. Even shots that don't protect from all the strains going around can mitigate the illness, Calonge said.

And he said he hopes this year's early arriving flu will follow typical patterns and peak in the next two or three weeks.

"In Australia, (the Fujian strain) followed the exact same pattern (as other strains)," he said.

WHAT YOU NEED TO KNOW ABOUT FLU

COMMON SYMPTOMS

Fever, usually 102 degrees Fahrenheit, but can go up to 104 degrees; lasts three to four days

Headache, sudden onset

Sore throat

Muscle aches

Coughing

Tiredness and weakness

Sneezing

Runny nose

Nausea and vomiting in young children

PRECAUTIONS

Clean hands often with soap and water or an alcohol-based hand cleaner

Avoid touching eyes, nose and mouth

Avoid close contact with people who are sick

STOPPING THE SPREAD OF GERMS

Cover nose and mouth with tissue every time you cough or sneeze

If you don't have a tissue, sneeze or cough into your sleeve, not into your hands

After coughing, sneezing or blowing your nose, clean your hands with soap and water or with an alcohol-based hand cleaner

Stay home when you are sick

Do not share eating utensils, drinking glasses, towels or other personal items

VACCINES

Strongly recommended for people over 65; those with chronic health conditions, such as diabetes, asthma, HIV/AIDS, kidney disease and cardiovascular diseases; pregnant women in the second and third trimester; people in nursing homes or chronic care facilities; and children and adolescents receiving long-term aspirin therapy.

INFORMATION

Available in English and Spanish on the Colorado toll-free hotline, 877-462-2911

Denver Post staff writer Kieran Nicholson contributed to this report.