This blog appears in the In-Depth Report Science at the Sochi Olympics

The Olympics are not just a chance for countries to bring home the gold. They also provide a perfect chance to spread infections all over the world. The Olympics are likely surpassed only by the annual Hajj Islamic pilgrimage to Mecca in the opportunity to rapidly disseminate infections. Let’s look at how.

Mass Gatherings

The Olympics pales in comparison to the largest gatherings, which are religious. The Hindu pilgrimage along the Ganges River, the Kumbh Mela, attracted 120 million in 2013; visitors may number 5 million on one day alone, but it lacks the global breadth of visitors. Kumbh Mela is thought to have contributed to the 1817-24 cholera pandemic, which spread from the Ganges to Kolkata and Mumbai, across India, and then was further disseminated by British soldiers and sailors to Europe and Asia.

The World Expo in Shanghai in 2010 attracted 73 million for a brief period. Other religious gatherings pale in comparison: Lourdes attracts 5 million/year, Manila’s Feast of the Black Nazarene 7-8 million in 2011. Other sports and political gatherings have generally been far less.

The annual Hajj pilgrimage has been a great place to study mass gatherings. The Hajj ritual attracts 2-3 million people from more than 183 countries to Saudi Arabia each year. Because the location of the gathering is always the same, it is an ideal place to study infectious disease mixing. The Islamic calendar is based on a lunar cycle, so the date and season of the Hajj shift every year, presenting additional challenges, like heat-related illnesses, some years. For example, in August, 1985, more than 18,000 needed treatment for heat exhaustion, there were 2000 cases of heat stroke and more than 1000 deaths at Hajj.

Previous infectious outbreaks at Hajj have included meningococcal infections, TB, pertussis, and influenza. Hajj has provided the opportunity to develop systems for real-time detection of diseases at mass gathering, as well as refinement of “global health diplomacy.”

Non-communicable diseases have had a larger impact than infectious diseases on deaths at mass gatherings. In particular, human stampedes and crush injuries have resulted in more than 7000 deaths and 14000 injured people over the past 27 years.

Infectious diseases at religious and sport events

While not likely quite as good as massive religious gatherings at disseminating infection, sports venues like the Olympics contribute their share to public health problems. For example, there have been these outbreaks of infections at mass gatherings:

2000-2001 - meningococcal outbreak at Hajj, led to global spread.

2002 - influenza in Salt Lake Winter Olympics

2006 - norovirus outbreak during the Football World Cup in Germany

2006 - chicken pox outbreak among members of the Maldives volleyball squad during the Asian Games in Doha, Qatar

2006 - leptospirosis in Germany among triathlon athletes

2008 - influenza World Youth Day, Sydney

2009 - Hajj, which took place during the influenza A H1N1 epidemic

2010 - measles at the Winter Olympics in Vancouver, Canada. The outbreak spread to remote areas of British Columbia, causing significant morbidity, especially among indigenous people.

What are the likely infections at mass gatherings?

Some of the likely infectious candidates are predictable, like norovirus, the highly contagious vomiting-and-diarrhea causing virus, which is notorious for outbreaks on cruise ships. Cholera has been a big problem in India, as noted above. Food and water-borne outbreaks can spread efficiently. For example, more than 50% of the ~12,700 attendees at the Rainbow Family meeting in North Carolina in 1987 became ill with an unusual strain of Shigella sonnei, due to contaminated drinking water and poor sanitation.

Outbreaks of meningococcal infections, which cause meningitis outbreaks, are less common at Hajj now, because of a mandatory vaccination requirement since 2002. Other respiratory transmitted pathogens include Legionella, tuberculosis, pertussis (whooping cough) and influenza. Flu is worrisome because of the potential for different strains to combine, as mentioned in my recent overview of flu, H1N-what?

Measles has the potential to be a huge problem, because it is highly communicable. Many countries in Europe, including Russia, have active, ongoing measles outbreaks.

Some less common bugs have surfaced, as well. For example, there was an outbreak of African tick-bite fever, caused by Rickettsia africae, among a group of participants in the “Raid Gauloises” in Lesotho and Natal, South Africa. This competition included multiple sports—rafting, horseback riding, trekking, and mountain biking. The attack rate ranged from 3.9-7.6% of participants, with those affected becoming ill with symptoms like headache, lymphadenopathy (swollen glands), fever, myalgias (muscle aches) and a typical rash called “tache noir.” There is a risk of acquiring the parasitic infection schistosomiasis from contact with contaminated water during swimming or water sports in South Africa.

Skin infections like MRSA (methicillin resistant Staph aureus) are frequently transmitted in gyms and locker rooms, or during close contact sports. Other odd outbreaks occur among wrestlers. There have been occasional outbreaks of molluscum, Herpes simplex (Herpes gladiotorum) and Hepatitis B among them. Unexpectedly, 1500 cases of Hepatitis B also occurred among those orienteering in Sweden.

Interestingly, intense exercise may increase an athlete’s susceptibility to infection, especially respiratory tract infections. Close quarters further facilitates spread of droplet and airborne infections.

Some infections likely are acquired not just directly at such sports venues, but through tourism around the event. Zoonotic illnesses from rabies, leptospirosis and tularemia are higher in Sochi than the average rate in Russia and, were it not for the Olympics being held in winter there, would pose an increased risk from people being active outdoors and being exposed to animals.

In 2016, the Olympics will be held in Rio de Janeiro—the first time South America has hosted the event. Dengue cases are common there. While malaria is not transmitted in Rio, ecotourism outside the city might expose visitors to that and to Leishmaniasis, a nasty parasitic infection transmitted by sandflies, as well as to Hepatitis A.

Exotic travel locales tend to lead to “loosening of sexual inhibitions.” Sexually transmitted diseases, including HIV are noted as a possibly high-risk public health problem associated with the Olympics. Presumably, excessive alcohol and drug use associated with sports events also increases this risk.

Besides these direct person-to-person forms of transmission, vector-borne diseases can potentially cause big problems. We’ve just seen that with the recent emergence of a viral infection, Chikungunya, in the Carribbean, where it has just become established for the first time. Previously, this virus was limited to Asia and Africa, then spread to Italy in 2007, before arriving in St. Maarten’s. Just in the past month, there has been an explosion in cases, now spreading throughout the Carribbean. This virus, like dengue, is transmitted by Aedes aegypti and Aedes albopictus mosquitoes. Asian tiger mosquitoes (A. albopictus) were introduced to the Americas in the mid-1980s, probably in old scrap tires with pools of standing water. Initial spread then followed the interstate highway routes. These specific mosquitoes can transmit these tropical diseases, allowing them to become established now in the western hemisphere. No doubt Chikungunya will soon follow dengue and move to the Florida coast and Tex-Mex border as well. All it takes is an infected traveler to be bitten by a mosquito, who then transmits it to another person. Or it could set up housekeeping in New York City, by the combination of travelers and global warming allowing the mosquito to propagate. Some worry that Yellow Fever could similarly become reestablished in the USA in this way, just as dengue did in the 1980s.

Planning considerations

At the Olympics, as for Hajj, planning for infectious disease has to take a number of factors into consideration. These include what diseases might be endemic in the region of the gathering, and what diseases might be circulating seasonally, like the current influenza. A particular problem is that air travel enables dissemination of an infection like the flu or measles, both of which are highly transmissible, before the incubation period is complete. Seasonal flu will not be readily detected by surveillance systems, unless a new strain emerges. Such surveillance systems, like GeoSentinel, are more likely to pick up a spike or cluster of unusual infections. For example, in 2000, 304 athletes from 26 countries participated in an endurance race in Borneo, Malaysia. After they returned home, a London GeoSentinal clinic identified a patient with suspected leptospirosis, an infection associated with exposure to water which has been contaminated by rodent waste during sports (think kayaking, swimming, for example). Within hours, other suspected cases were identified in Canada and the US. An alert enabled others who were exposed to receive prompt antibiotic treatment.

Projects like HealthMap and ProMed are invaluable resources, gathering data from search engine queries and case reports, serving as an early warning system. Besides, they are just fun sites to browse, as there is often something weird and new being reported.

The scope of the logistical planning involved is also intriguing. Modeling helps in evaluating different scenarios and predicting problem spots. But think of the magnitude of concerns—from transportation and moving people without provoking riots, stampedes, and crushing deaths, to housing. Think of providing food and water for 3 million in 1 week at Hajj. How do you handle sanitation and waste disposal? It seems miraculous that there are not more infectious outbreaks linked to mass gatherings. Add to this the number of countries sending visitors, the various languages, and the need for cooperation between so many countries, and the success becomes even more impressive. Imagine if such cooperation occurred in other situations.

From the infectious disease perspective, surveillance is essential, as are strict regulations to try and prevent the spread of communicable disease. Mass gatherings are not the place to try raw goat milk for all, or undercooked meat. Sanitation needs to be efficient. And it is imperative to insist on vaccinations, as Saudi Arabia did for reducing meningococcal infections during Hajj.

What to watch for in Sochi

So the big things to watch for, bug wise, are influenza and measles rapidly spreading. Colds, strep throat, and similar common infections are readily spread in close quarters and by athletes pushing themselves to compete, even when ill. Twenty years ago, there was a memorable outbreak of diptheria in Russia; fortunately, that has been well-controlled.

Drug-resistant tuberculosis (MDR-TB) is rising in Eastern Europe. The Russian Federation ranks third globally in total cases of multi drug-resistant TB (MDR-TB), beaten only by China and India. A scary recent genetic study of 1000 TB isolates from Russia found not only widespread drug resistance, but mutations that enabled the TB to spread more readily.

If the flu strains commingle, we could see new pandemic strains emerge, with athletes bringing home far more than the gold.

What can we do to reduce risk of infections?

Several diseases are highly contagious before a person develops symptoms, including influenza, measles, and chickenpox. This obviously makes them of great concern wherever large numbers of people gather. Just as Saudi Arabia now requires meningococcal vaccine to attend Hajj, thought should be given to requiring some vaccinations to attend sports and other mass gatherings—particularly measles and influenza.

To protect yourself—at home and abroad—be sure to have your vaccinations:

Hepatitis A & B

measles-mumps-rubella (MMR) vaccine,

diphtheria-tetanus-pertussis vaccine,

varicella (chickenpox) vaccine,

polio vaccine, and your yearly flu shot.

Without those precautions, Olympic visitors and participants in other mass gatherings may get far more than than they bargained for when they purchased their tickets. Additionally, I always get a baseline TB test before I leave and after I return from higher-risk travel overseas.

I also keep my Kwikpoint translator card handy (most recently, it was handy on an international flight where attendants couldn’t communicate with a passenger seated near me). I love those cards.

So enjoy your travels. I’m going to sit back and watch for any new diseases that might emerge, and marvel at how epidemiologists do their sleuthing. Disease detection is a great spectator sport!


"Molecules to Medicine" banner © Michele Banks

Ski jump courtesy shayhaas - flickr- CC

Hajj courtesy Al Jazeera- CC

Measles and tuberculosis maps, courtesy WHO

Aedes albopictus Tiger mosquito - CDC