|Ask the expert
As part of its coverage of the current flu crisis, Al Jazeera will be interviewing a medical expert to answer questions sent in by you.
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Some of the questions will be read and answered on air.
"And that leads to the question of whether number six on the pandemic scale is called by the WHO [the World Health Organisation]. Whether it is, in fact, then defined as a real pandemic."
Level six is defined as human-to-human sustained transmission in at least two regions or continents of the world and is the highest of the WHO's rankings.
The alert level now stands at five.
Hull reported: "We already have Mexico and the US. Now we have Europe and the possibility that this is not only connected to those who have been in Mexico. That is key to the progression of this whole thing towards pandemic status."
The nurse has since recovered, the health ministry said.
It is the second case of human-to-human transmission within a country other than Mexico.
Spain reported a case of human-to-human transmission to a person who has not visited Mexico. The person had contracted the flu from a partner who had travelled to the Latin American country.
Tests are also under way in the UK on a possible human-to-human transmission.
The WHO defended itself on Friday from accusations that it responded too slowly to the epidemic when it was initially notified of its potential early on April 24.
"There are case of influenza all the time, but once we knew that this illness was caused by a new influenza virus ... we moved into operation within a matter of hours," Thomas Abrahams, a WHO spokesman, said.
"One of the things we are doing internally is documenting everything we have done, when we did it and how we have done it," he said.
Worldwide there are 13 confirmed deaths caused by the H1N1 virus - one in the US and the rest in Mexico.
The WHO also said on Friday that 331 confirmed cases of infection by the virus had been found globally.
Hull said that the number of confirmed cases was "rising fairly rapidly."
"But it is still a figure that is quite well below the individual national figures that are being reported by health ministries around the world which put the number of confirmed cases at around 500.
Twelve confirmed in Mexico out of 159 suspected. One death in the United States
Countries with confirmed cases: Mexico, the US, Canada, New Zealand, Spain, Israel, Britain, Germany, Austria, Switzerland, Netherlands, Costa Rica
Countries with suspected cases: Australia, Brazil, France, Chile, Denmark, Colombia, Germany, Norway, South Korea, Guatemala
Annual influenza epidemics are thought to result in three to five million cases of severe illness and between 250,000 and 500,000 deaths around the world, WHO says.
"That's because those cases are then vetted by the WHO so that the WHO can in its own time independently confirm."
Dr John Simons, a consultant in infectious disease and tropical medicine, told Al Jazeera from Hong Kong: "It is a new flu virus and it has the potential of causing a pandemic.
"All of the precautions taken so far have been very justifiable and we need to be prepared for a pandemic.
"However, having said that, we need to look at this with some sort of perspective.
"Firstly, ordinary seasonal flu kills between 200,000 and 500,000 people throughout the world every year, and in the United States 36,000 people.
"So far, this new H1N1 virus is appearing to act rather like ordinary flu.
"The difference is, however, that this is a new virus and nobody has any immunity to it.
"So it is likely to sweep around the world and probably will cause a pandemic. And will cause significant morbidity and some degree of mortality."