What real threat does Zika pose to the Rio Olympics? History has an answer

Updated 8:48 AM EST, Fri February 12, 2016

Story highlights

Mass gatherings are always associated with risk, ranging from traumatic injuries to infections

Brazil is launching a herculean effort to fumigate Rio of mosquitoes

Olympics officials are not considering postponing or canceling the Games

(CNN) —  

Well before the Zika epidemic began in Brazil last year, Olympics organizers knew they would face a challenge in keeping the approximately 16,000 athletes and 600,000 visitors to Rio de Janiero healthy.

Mass gatherings are always associated with risk, ranging from traumatic injuries to infections. But in many ways, the Zika virus is a unique foe when compared to the types of infections expected by medical officials in charge of the safety at such gatherings. If Brazil and the International Olympic Committee aren’t up to the challenge, as they think they are, their decision to proceed with the games could detrimentally impact much of the globe.

The recent history of viruses at mass gatherings

A limited outbreak of 82 cases of measles occurred around the 2010 Winter Olympics in Vancouver, British Columbia. At least two visitors spread the virus at one or more Olympics venues, and at least one person infected in Vancouver then traveled along Highway 97, spreading the virus on that route into the interior of British Columbia.

Norovirus – the all-too-frequent cause of vomiting and diarrheal illness commonly associated with cruise ships in recent years – likes big events, too. It spread to 65 people at the 2006 FIFA World Cup in Germany. Carefully preplanned disease surveillance systems put in place before that event helped officials detect the outbreak early and limit its spread.

Sixteen years ago 90 people came down with meningitis in nine European countries and 14 people died. Epidemiologists tracked the outbreak to pilgrims returning from the Hajj. This annual trek of more than 2 million Muslims to Mecca has in recent years attracted concerns over its potential to distribute the MERS virus in a similar fashion.

The 2012 London Olympics went off without a hitch, though, thanks to the most comprehensive surveillance and triage system for a large event the world has ever seen. The games have made a lasting impact on the public health infrastructure in the United Kingdom, which now benefits from real-time data about syndromes: the collections of symptoms patients complain about. Detecting patterns in early symptoms is critical to recognizing new emerging threats quickly, permitting public health authorities to devote appropriate resources to stop their spread.

What does this mean for the Rio Olympics?

While Rio 2016’s health and safety infrastructure will surely learn from London’s experience, the Zika virus poses a particular challenge in that 80% of cases have no symptoms, and thus won’t get detected in a syndrome surveillance system.

The mosquito population primarily spreading the virus reaches its lowest numbers during the Brazilian cool season, which includes August and September when the Olympics and Paralympics will be held. But the temperature still hovers between 65 degrees F at night and 75 degrees in the day, so the mosquitoes bite year-round in the region. Brazil suffered a chikungunya outbreak of several hundred cases in mid-September 2014. It quickly bloomed into 722 probable cases in 10 cities by the first week of October, and that’s a virus borne by the same mosquitoes.

Freed from their natural environs, we know that up to half of all travelers engage in casual sex, which can also transmit Zika if they don’t use condoms. Travelers can also spread Zika to sexual partners back home, or to native mosquitoes who will transmit it locally. While Brazil will be enjoying its mild winter this August, many travelers to the Rio de Janeiro Olympics will return to Northern Hemisphere countries such as the United States precisely when mosquito populations are peaking.

Brazil is launching a herculean effort to fumigate Rio for mosquitoes, and most of the Olympics events will be held in that one city, but it has a native population of 12.9 million sharing a varied geography that includes rain forest and beaches. The hardy Aedes aegypti mosquitoes that carry Zika can reproduce even within a dab of water lying in an overturned bottle cap.