“We’re saying there have been at least a million cases of this new H1N1 virus in the United States so far this year. “

That’s according to the Centers for Disease Control and Prevention (CDC) which held a press conference on Friday which shed some more light on the epidemiology and spread of the disease.
So how was this huge figure (over thirty times the number of confirmed cases) calculated?

“ There have been community surveys in a couple of areas looking at influenza-like illness in areas where we know there’s a lot of the strain circulating and in many of those communities, they’re reporting proportions of about 6% of their community members having had an illness that’s consistent with the new virus. “

The survey that the CDC describe in most detail was in New York where 6.9% of respondents had experienced a flu-like illness during a three-week period in May. That works out at about half a million New Yorkers – and that’s excluding anyone who might have had a subclinical infection.

But surely all that sneezes isn’t swine flu? Or perhaps it is: the CDC spokeswoman said that “from their viralic testing they knew pretty much that most of that influenza-like illness [during the period in May] was cause by this new H1N1 strain.” It would be interesting to know what the criteria were for flu-like illness.

The press conference also confirmed once more that the epidemiology of H1N1 is very different to other influenza strains.

“We’re seeing high rates of illness among people under 50.  The highest rates are in those under 25.  When we look at hospitalized cases, nearly 80% of people who have been hospitalized in the U.S. and reported to us have been under 50.   The median age of hospitalized cases is 19 years old. The median age of those who have died is 37”

Around three quarters of those who have died have underlying conditions. Therefore, if my maths is correct, around 30 previously healthy people have died from H1N1 in the United States.

Second death in the UK

Back in the UK, a 73 year old man from Glasgow died from the H1N1 virus over the weekend taking the number of deaths in the UK to two.

The spread of the infection shows no sign of slowing down. I spoke to a consultant in Birmingham on Friday who told me that they were diagnosing around a hundred patients a day in his hospital’s A&E department. He also said that at least thirty children in the area have been hospitalised with swine flu since the outbreak began.

Glastonbury fever

The much feared swine flu fest at the Glastonbury festival hasn’t yet materialised. Just three revellers (two students and a child) were sent home with flu like symptoms.

“This was anticipated,”
a spokesman said. “There is no more risk here than anywhere. The figure of three in 177,000 people is regarded as very low.”

He might be speaking too soon though as you wouldn’t expect to see any new cases from spread at the festival until the start of this week.

Tom Nolan is the clinical community editor of doc2doc, the BMJ’s professional networking community.