April 03, 2012
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Mass gatherings pose threat to the spread of infectious diseases

Integrating scientific, technological components necessary to minimize

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This summer, millions of people will converge in London for the 2012 Olympic Games. Besides the increased risk for terrorism and accidents, mass gatherings such as these pose a unique threat to the spread of infectious diseases.

“Mass gatherings pose the usual concerns with people in close contact, such as viral respiratory tract infections, including influenza, measles and tuberculosis,” said

Herbert L. DuPont, MD, an Infectious Disease News Editorial Board member. “There are also more remote concerns, such as pandemic flu, and the introduction of diseases from distant locations, such as multiresistant TB, STDs and low-dose enteric infections that show person-to-person spread.”

The phrase “mass gathering” is not well defined. According to an article in a series of papers published in The Lancet Infectious Diseases, a mass gathering can include as few as 1,000 people or more than 25,000 people. According to WHO, mass gatherings include, “more than a specified number of persons at a specific location for a specific purpose for a defined period of time … if the number of people attending is sufficient to strain the planning and response sources of the community, nation or state hosting the event.”

Kamran Khan, MD, said certain diseases may rapidly spread to people from parts of the world where the disease does not currently exist.
Photo courtesy of St. Michael’s Hospital

New diseases are emerging and many previously controlled diseases are re-emerging, leading to increasing serious implications worldwide. Scientific and technological components exist and are necessary to mitigate the risk for infectious disease spread during mass gatherings, but the two components are not well integrated. Research is necessary to bridge the gap between these complementary components, and this research requires cooperation between local and international stakeholders.

The annual Hajj, when Muslim pilgrims attend sacred rituals in Mecca, Saudi Arabia, is considered the largest annual mass gathering in the world. The reported attendance was more than 2.5 million people in 2009, despite warnings about pandemic influenza.

As previously reported in Infectious Disease News, the public health response in Saudi Arabia has evolved in recent years to include health screenings as people enter the country, free health care during the Hajj, stepped up infection control efforts in hospitals, more personnel to staff health care facilities surrounding the pilgrimage sites, and most recently, boosted surveillance strategies that are being regarded as groundbreaking within public health circles.

Yet, other types of mass gatherings pose a potential threat. Examples include the summer and winter Olympic Games, rock concerts and political rallies. The wedding of Prince William and Catherine Middleton in 2011 drew an estimated 1 million visitors to London. Peaceful protests in Tunis, Tunisia, and Cairo, Egypt, drew millions of protesters. The Kumbh Mela, a Hindu pilgrimage held at many locations along the Ganges River, attracted 70 million pilgrims in 2007.

Spread of diseases

Infectious disease spread during mass gatherings is a prominent issue. During the 2010 Winter Olympics in Vancouver, Canada, a measles outbreak spread to remote areas of British Columbia, causing significant morbidity. Likewise, a chicken pox outbreak affected the 2006 Asian Games in Doha, Qatar, but was successfully managed with quarantines, antiviral drugs and vaccines.

There are several ways that communicable diseases can be transmitted at mass gatherings. According to an article in The Lancet Infectious Diseases, gastrointestinal disease outbreaks are possible despite advances in food and water hygiene in developed countries. In 1987, for example, an outbreak of multidrug-resistant shigellosis affected more than 50% of the attendees at the annual Rainbow Family Gathering in Nantahala National Forest, North Carolina.

“As far as infectious diseases, I think the biggest risk to people going to mass gatherings is some type of food or waterborne gastrointestinal infection, caused by eating or drinking something that is contaminated,” Commander Gary Brunette, MD, MS, branch chief of travelers’ health at the National Center for Emerging and Zoonotic Infectious Diseases of the CDC, told Infectious Disease News. “In some destinations, like South Africa and China, we would advise people to drink bottled water. For Europe, we don’t make that recommendation because most European water supplies are considered safe.”

Gary Brunette, MD, MS
Gary Brunette, MD, MS

Respiratory transmission is also a mechanism of infectious disease spread that can affect mass gatherings. In July 2008, there was an outbreak of influenza reported at the World Youth Day in Sydney, Australia, caused by several strains of influenza viruses. Other influenza outbreaks include the Winter Olympics in Salt Lake City in 2002, and pandemic influenza H1N1 at music festivals throughout Europe. Aside from influenza, TB and legionellosis also pose a risk at mass gatherings.

Vector-borne transmission of infectious diseases poses a unique risk, as they can cause outbreaks in areas where the disease is not endemic, and local health care officials may not recognize the disease if it has been eliminated from their country. Malaria, dengue, West Nile encephalitis and yellow fever can occur outside of endemic areas if an infected traveler visits locations outside of the endemic area.

“People attending mass gatherings are potentially bringing diseases from their own particular geography and could introduce a disease into the mass gathering,” Kamran Khan, MD, an infectious disease physician at St. Michael’s Hospital in Toronto, said in an interview with Infectious Disease News. “Some of these diseases could then rapidly spread to other individuals who are at the gathering, who might be coming from parts of the world where the disease doesn’t [currently] exist.”

Yet another type of infectious disease threat at these types of gatherings are zoonotic infections, the most common being Escherichia coli O157. An outbreak of this infection occurred at the Glastonbury Festival in the United Kingdom in 1997. An outbreak of leptospirosis, another zoonotic infection, was reported in Germany among triathlon athletes in 2006.

Infectious disease surveillance

According to Khan, the hosts of mass gatherings have traditionally focused on what they can do in their own territory, where the event is being held, to prevent the spread of diseases. For example, in the case of the 2012 Summer Olympics in London, officials are working to ensure that surveillance systems are on heightened alert, and that they can respond quickly to an outbreak.

“The challenge with this is that you’re waiting for an event to happen, and then trying to detect it early and deal with it,” Khan said. “So it’s not really preventive; it’s more reactive.”

In another article in The Lancet Infectious Diseases, Khan and colleagues proposed a surveillance model that focuses not only on the host city itself, but also raises awareness of what is happening in the world during the time leading up to the gathering. The information takes the form of official government reports of disease events, and using Internet-based tools such as websites, blogs and social media.

“Infectious disease surveillance for mass gatherings can be directed locally and globally,” Khan said. “The two complement each other; however, intelligence from these two levels is not well integrated.”

In the case of the 2012 Summer Olympics in London, the UK’s Health Protection Agency has well-established systems for identifying and monitoring national and international public health issues to ensure that appropriate and timely action can be taken, according to Brian McCloskey, MD, director of the Health Protection Agency for London.

Brian McCloskey, MD
Brian McCloskey, MD

“Surveillance by itself does not reduce the risk of [infection], but it does increase the likelihood that we will detect anything happening much earlier and have more time to deal with it,” McCloskey told Infectious Disease News. “Surveillance does not reduce the risk, but it does mean that small problems are less likely to develop and become big problems.”

McCloskey said the Health Protection Agency has been in contact with colleagues who manage the Hajj in Saudi Arabia to exchange ideas on managing mass gatherings. He added, however, that the Olympics differs from the Hajj, in that the crowds are not as dense and the risk of spreading infectious disease, thus, is lower.

Effective planning and research

According to another article in the series published in The Lancet Infectious Diseases, developing measures for planning and handling of health risks during mass gatherings “will strengthen global health security, prevent excessive emergency health problems and associated economic loss, and mitigate potential societal disruption in host and home communities.” To prevent the spread of infectious disease, management is necessary before, during and after the event, as has been demonstrated in planning for the Hajj.

Lessons can be learned from the 2009 Hajj, which took place during the influenza A H1N1 pandemic. The Saudi Arabia government launched a mobile phone-based platform to communicate and gather public health intelligence, enabling field investigators to identify cases of influenza, gather information and transfer real-time information to public health decision-makers.

As for the 2012 Summer Olympics in London, the Health Protection Agency is taking lessons from the Hajj and working with real-time surveillance to identify potential risks. Khan’s surveillance model is part of the plan.

“This is the first time that we’re going to get some feedback from a host of a mass gathering to see how this works, with the intention of continuing to refine it and improve it for future events,” Khan said. “We certainly see this as something that can be utilized around other mass gatherings.” – by Emily Shafer

For more information:

  • Abubakar I. Lancet Infect Dis. 2012;12:66-74.
  • Khan K. Lancet Infect Dis. 2012;doi:10.1016/S1473-3099(11)70313-9.
  • Memish ZA. Lancet Infect Dis. 2012;12:56-65.
  • Tam JS. Lancet Infect Dis. 2012;doi:10.1016/S1473-3099(11)70353-X.

Disclosures: Drs. Brunette, DuPont and McCloskey report no relevant disclosures. Dr. Khan holds intellectual property in technology related to global travel and the spread of infectious diseases.


What precautions should local health authorities take to minimize disease occurrence for the upcoming Olympics?