Federal health officials say at least 16 more children died of the flu over the past week and more states are reporting high levels of illness. In a briefing Friday, the Centers for Disease Control and Prevention said the flu outbreak is responsible for at least 53 child deaths so far this season.

"Hospitalizations are now the highest we've seen," said CDC Acting Director Dr. Anne Schuchat, who called the flu one of the biggest health threats currently facing the U.S. She said the cumulative rate of hospitalizations for serious cases of flu is now even greater than in the previous high season of 2014-15. People age 65 and over have the highest rate of hospitalization for the flu.

One of every 14 visits to doctors and clinics were for symptoms of the flu. That's the highest level since the swine flu pandemic in 2009, the Associated Press noted.

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High levels of flu-like illness were reported in 42 states, up from 39 states the previous week, and cases were geographically widespread across every state but Oregon and Hawaii.

In one sign of good news, Schuchat said the outbreak appears to be easing up in the West. But there are probably several weeks left of increasing flu activity this season, she warned.

"We aren't out of the woods yet, but there are steps everyone can take to fight the flu," Shuchat said.

She noted that half of the children who've been hospitalized with flu this season did not have underlying medical problems like asthma. Doctors say if a person seemed to be getting better from the flu and then suddenly takes a turn for the worse, that's a sign they need medical attention right away.

"Influenza can be followed by a bacterial infection like pneumonia," Schuchat explained.

That dangerous pattern of getting better then worse was seen the case of 5-year-old Eli Snook. After the Georgia boy tested positive for flu, he was treated with the antiviral drug Tamiflu and antibiotics and seemed to be recovering.

"After he got well from the flu, a few days later, he got sick again," his mother Leota said. Eli was hospitalized and placed in a medically induced coma while doctors performed a CT scan and spinal tap. They discovered the virus had spread to his brain.

"His brain swelled past the point of no return and they told us that he was brain dead," his father Aaron said. Little Eli did not survive.

Dr. Claire Bocchini, an infectious disease specialist at Texas Children's Hospital, told CBS News, "It is very important to know the signs and symptoms that indicate when someone is very sick from the flu and needs help right away."

The CDC says emergency warning signs in children include:

Fast breathing or trouble breathing

Bluish skin color

Not drinking enough fluids

Not waking up or not interacting

Being so irritable that the child does not want to be held

Flu-like symptoms improve but then return with fever and worse cough

Fever with a rash

In adults, emergency warning signs from flu may present as:

Difficulty breathing or shortness of breath

Pain or pressure in the chest or abdomen

Sudden dizziness

Confusion

Severe or persistent vomiting

Flu-like symptoms that improve but then return with fever and worse cough

If you or your child have these symptoms, seek medical treatment right away.

Schuchat stressed that the CDC continues to recommend people get flu shots, even though the vaccine's effectiveness is lower than in some years. Canadian researchers reported Thursday that this year's flu vaccine is less than 20 percent effective against the most dominant strain of the virus. Schuchat said the vaccine still offers some protection and can reduce the severity of illness if you do get infected.

Schuchat, a 30-year veteran of the CDC, took over as acting director this week after Dr. Brenda Fitzgerald resigned amid controversy over financial conflicts of interest.