Wales is heading for a 10-year flu high with younger people worst affected, according to health officials.
Eleven patients with the H1N1 swine flu virus are in critical care and 17 with flu-like symptoms in intensive care.
Public Health Wales said there was a huge increase in patients last week and it is the worst "flu wave" since 2000.
There were 85.5 consultations per 100,000 people, compared to just 22.6 the previous week, with more young people affected.
Consultant epidemiologist at the health body Dr Brendan Mason said: "The flu wave in Wales is as bad as it has been for 10 years.
"Our information is based on consultations with GPs and it's data we have kept over 25 years, so we know what the pattern of flu normally is.
"We've seen an increase in consultations for flu over two to three weeks and following the normal pattern, we would expect it to continue to go up for the next three to five weeks."
The same week last year saw a total of just 22.7 consultations per 100,000.
This week's figures show 15 to 24-year-olds were the most badly affected age group with 170 consultations per 100,000 population.
But vaccination uptake in the under-65s as a whole is down 10% on last year to 40%.
Dr Mason said it was not too late for those in the most at-risk groups to get a flu jab.
He said: "Flu is a serious disease and that's why we go to so much trouble to promote immunisation.
"When you look at flu over the last 20-30 years in Wales, we've probably seen 1,000 to 1,500 deaths as a result of flu.
"All the data we've got on the flu that's circulating shows that the strains that are causing the disease in Wales are covered by the vaccine so it's possible to protect yourself."
He said the swine flu virus was behaving as officials expected.
"Pandemic viruses always become seasonal flu viruses and have the potential to cause serious disease," he added.
"Because last year it was nowhere near as bad as some of the worst forecasts, we tend to become a little bit complacent about flu and think it's not as serious as it seems."
A Welsh Assembly Government spokesperson said: "For those who are 65 and over, or under 65 with a chronic condition or who are pregnant, they should get their free seasonal flu jab, as this is the simplest way of protecting themselves this winter. If you haven't had it yet, contact your GP."
For advice, contact NHS Direct Wales on 0845 46 47 or visit www.nhsdirect.wales.nhs.uk.