Millions of pilgrims who gather in Mecca for the annual haj pilgrimage risk creating the conditions in which a pandemic strain of flu could emerge

Reuters:

"It's the worst case scenario we can have," said Didier Pittet, director of the Infection Control Programme at Geneva's University Hospitals.

Around 2.5 million Muslim pilgrims from over 160 countries head for Mecca each year in one of the world's biggest religious rituals. The next haj is expected to start in January.

The deadly H5N1 form of bird flu has killed 67 people in five countries in Asia over the past two years. Indonesia, the world's largest Muslim country, has confirmed seven deaths.

The virus cannot pass among people the way ordinary seasonal flu does, but experts fear it could mutate into a form which can be transmitted from person to person.

The risk of mutation would be increased if anyone with bird flu came to Mecca and mingled with people with seasonal flu among the huge crowds.

"What Saudi authorities deployed in terms of efforts and prevention measures is remarkable," said Pittet, who leads a campaign by the World Health Organisation to prevent infection among patients.

"But what will be terrible is that by bad luck bird flu and common flu viruses come in contact".

"If Saudi authorities discover a sporadic human case of bird flu in Mecca then extreme and immediate action will be needed. If a second and similar case is spotted in the same area then you have a clustering of cases, you suspect there are other forms of transmission," Pittet said.

"If they discover a human-to-human contamination of bird flu they should call off the haj," he added.

In addition to regular health checks imposed on foreigners wanting to visit Saudi Arabia, authorities plan a campaign soon to widen vaccination against common human flu among pilgrims, said Amine Mishkhas, head of infectious diseases at the health ministry.

"We have spent 25 million riyals ($6.7 million) to treat and prevent flu especially among people in direct contact with birds," Mishkhas said.

It has also opened centres in three key cities, including Jeddah --a key entry point for pilgrims -- to track down birdflu contamination cases, Mishkhas added.

Throughout Saudi history, cities like Mecca, Medina and Jeddah have been worst hit by deadly diseases like plague, cholera and meningitis during the haj, he said.

"We are making sure only fit and healthy Muslim can enter Saudi Arabia for the haj," said Sahal al-Sabban, a senior official at the Pilgrimage Ministry.

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