What do the numbers mean?
Apologies for constantly updating the figures, but I feel it's necessary at the moment: first, because the virus is continuing to spread; second, because of the dramatic surge in cases in the southern hemisphere.
The World Health Organization's latest figures show that 73 countries have officially reported 25,288 of influenza A(H1N1) infection (more commonly known as swine flu) including 139 deaths. It's worth comparing that with , when there were 17,410 cases in 62 countries and 115 deaths.
It's interesting to see the surge in cases over the past week in the southern hemisphere, which is entering its winter flu season. Australia's cases have leapt from 297 to 1051. Chile's cases have jumped from 250 to 411, with one death.
The UK has also seen a big increase. A week ago, the WHO reported 229 cases; today it had 557 (and remember that the WHO figures always lag behind national statistics by a few days).
If you are keeping track of what's happening in the UK, the more up-to-date figures are these:
• in Scotland, , bringing the total there to 232;
• in England, ;
• add four cases in Northern Ireland and two in Wales for a total of 664 - please forgive me if my arithmetic fails me at any point.
10 of the confirmed cases in Scotland are in hospital, including three in intensive care. Seven health care workers are now also among the confirmed cases. It's worth stressing yet again that the vast majority of people who have contracted swine flu have got mild symptoms.
So with 664 confirmed cases in the UK and more than a thousand in Australia, will a pandemic be declared by the WHO - and if so, when? :
"Phase 6, the pandemic phase, is characterized by community level outbreaks in at least one other country in a different WHO region in addition to the criteria defined in Phase 5. Designation of this phase will indicate that a global pandemic is under way."
You might argue that we are already there. But the WHO is looking for what it calls "sustained disease outbreaks" in the community. We have plenty of these in North America, and are . 
, Director of Public Health Strategy at the Health Protecgtion Agency, we are not there yet: "The number of sporadic cases remains under twenty. These are confirmed cases of infection, but where there's no obvious link with travel or a known case".
Professor Kessel said that "we would need to have a significant number of people where you really don't know how they have got it, for it to be classified as sustained community transmission. We are getting closer to that, but are not there yet."
Finally, a quick update on anti-virals and potential side-effects, which some have asked me about. Professor Kessel said that Tamiflu has so far been used mostly for children in the UK because of the outbreaks in schools.
"There have been reports of some side-effects," he said. "The most common have been nausea and stomach pain, which is in line with the manufacturers' written warnings. At the HPA, we have reiterated the advice that it's best taken with food, as this seems to help."
Professor Kessel said that when anti-virals were prescribed, the HPA was very clear that this was advisory: "It's up to parents and their children together to decide whether or not to take Tamiflu - there is no obligation to comply."
I'm 
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