Mass gatherings like the London 2012 Olympics carry health risks that may threaten vulnerable people worldwide, public health experts say.

This week's issue of the medical journal The Lancet Infectious Diseases series includes a "call to action" on tackling health security and other risks of mass gatherings for sports, social or cultural events. Travellers can introduce infectious diseases to a host nation or to their home country when they return, the researchers warned.

Traditional surveillance focused on the city and country holding a mass gathering so that authorities could quickly detect a problem and arrange for medical and public health responses.

Now, new technologies that look at how people move within a mass gathering offer insights into how the spread of disease can be affected by crowd behaviour, said Dr. Kamran Khan of St. Michael's Hospital in Toronto, an author of one of the six articles.

For example, there was an outbreak of influenza during World Youth Day in Australia in 2008.

The papers included expertise from Britain and Saudi Arabia, which hosts the Hajj pilgrimage, when about three million pilgrims take part in the world's largest annual gathering.

Mass gatherings "can pose substantial risks to global health security and present challenges for surveillance of the spread of such diseases to new ecological settings and vulnerable populations," the World Health Organization's John Tam and his co-authors wrote in another paper.

Vulnerable populations include people with low incomes living in places with inadequate access to vaccines and antimicrobial drugs for infections such as polio, they said.

Proven mitigation steps such as clinical and laboratory services reduce the harmful health consequences of mass gatherings while providing lasting value to society, the authors said.

They called for public health moves such as promoting smoke-free environments to prevent fires and state-of-the-art approaches for the early detection and monitoring of diseases such as using cellphones to gather and communicate information in real time.