Kit Roberts
Experts have warned about the symptoms of a new variant of the flu which is moving rapidly through the US.
We are in the middle of winter, and flu season is well and truly upon us, and now a new strain of 'superflu' is here, according to experts.
This has some different symptoms from the more common strains that you might expect to see, or indeed pick up, during the winter months.
Alarmingly, the new strain has not been seen in humans before.
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CDC data from the week that ended on December 27 showed 'very high' reports of influenza in some 32 US states, an increase of 10 from 22 the previous week.
But what are the symptoms of the new strain which appears to be moving through the US?
The strain is called subclade K, officially known as H3N2, due to it coming from the influenza A H3N2 subtype of the virus.
Dr Juanita Mora is a national spokesperson for the American Lung Association, and explained some of the signs to watch out for with the strain.
Speaking to NBC Chicago, she warned that the fever may not respond to over-the-counter medications such as Ibuprofen and Tylenol.
In a statement, she said: "This new strain has symptoms of really high fevers.
"It has a really bad cough that won't go away, very phlegmy, and also vomiting and diarrhoea and lots of joint aches as well as muscle aches."
Dr Mark Loafman, who works as a family doctor at Cook County Health in Illinois, warned of 'more fever with the flu this year than people are accustomed to', and that this flu can last for five to seven days.
"And that's worrisome," he said. "You feel ill, you feel sick, and you worry that you're not getting better."
The data from December shows around one in three flu tests coming back positive, which was an increase of 21 percent from the week before which had been at one in four.
Normally, for flu season, the US looks at what has happened in the Southern Hemisphere as a benchmark for how the upcoming flu season will be, and to watch for any new strains.
Countries such as Australia and New Zealand have flu season before the US, so they can give some insight.
This year, the Doherty Institute for Infection and Immunity in Australia said flu season 'differed from what is typically observed'.
It added that at the end of the season, a fast-spreading H3N2 variant emerged and, in August, was a leading cause of respiratory-related deaths in Australia.'