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The Olympics and the risk of exporting diseases

The likelihood of tourists becoming infected with the dengue or Zika virus is low, but critics point to irresponsibility in the staging of the event

Zika_ArosFreepikIt was already expected to be memorable. With the approach of the Olympic Games at the height of the Zika epidemic in Brazil—from January to early May 2016, there were 138,000 cases, 27.5% in the state of Rio de Janeiro—it was natural for questions to arise about the health risks of the 10,000 athletes and 500,000 tourists expected for the event. And arise they did.

In February 2016, two professors of New York University (NYU), Lee Igel, an expert in sports physiology, and Arthur Caplan, head of the bioethics division of the medical school at the university, wrote an opinion article for Forbes magazine suggesting that the games should be canceled, postponed or moved to another location. They pointed out the social and economic ills of Rio de Janeiro and Brazil and said it would not be safe to go to the Olympics amid the Zika epidemic.

At the time, the epidemic had reached its peak. According to data from the Ministry of Health, in February 2016 there were 53,000 Zika cases and the state of Rio de Janeiro had one of the highest rates of infection. Then the epidemic cooled off.

In May, Igel and Caplan along with biologist-attorney Amir Attaran, of the University of Ottawa, Canada, and historian-geographer Christopher Gaffney, of the University of Zurich, Switzerland, sent an open letter to the Director-General of the World Health Organization (WHO), Margaret Chan. Nearly 230 researchers from various countries signed the document, which recommended postponement or change of venue for the Olympic and Paralympic Games.

In addition to concerns about the health of the athletes, the authors expressed fear that the more aggressive Brazilian virus would spread to other countries. Even though the games will take place in winter, the lowest period of activity for the mosquito transmitting the Zika virus, Attaran and his colleagues argued that there was a risk of visitors being infected and then returning to their home countries with the Brazilian Zika, which would be a problem in Northern hemisphere countries, where it would be summer. They concluded the letter by saying that not revising its position on the games was “an irresponsible attitude.”

The document provoked a reaction from national and international health authorities. At the Oswaldo Cruz Foundation (Fiocruz) of Rio de Janeiro, the team led by epidemiologist Claudia Codeço wrote an article in response to Attaran and his group. In the article, published in the June 2016 issue of Memórias do Instituto Oswaldo Cruz, the researchers summarized studies on the dynamics of mosquito-borne diseases, especially dengue, and supported WHO’s position that the risk of spreading the Zika virus would be low and that there was no justification for changing the date or location of the event. In August the weather in Rio de Janeiro is dry and the temperature ranges between 19 and 26 degrees Celsius—with an average less than 22 degrees, much below the ability of the Aedes aegypti mosquito to transmit dengue. In addition, the researchers noted that laboratory tests had shown that Aedes aegypti  transmits Zika virus fever less efficiently than dengue.

“The mosquito is still there, but its numbers decrease because of a change in its natural dynamics and rate of reproduction,” says physicist Marcelo Gomes, of Fiocruz, co-author of the article and an expert on computer models of mosquito propagation. The available data on Zika, according to Gomes, indicate that the number of cases is declining in the city of Rio de Janeiro. “They dropped from 2,100 in the third week of February 2016 to 208 in the first week of May 2016,” he says. “This sustained reduction is consistent with the dynamics observed for dengue.”

As soon as they learned of the Attaran letter, physician and epidemiologist Eduardo Massad and physicist Francisco Bezerra Coutinho, both professors at the University of São Paulo (USP) and experts in mathematical models that simulate the spread of diseases, prepared a response. With Annelies Wilder-Smith, infectious diseases professor at Nanyang Technological University in Singapore, they wrote a letter, published in the June 2016 issue of The Lancet, which argues that the individual risk of a visitor being infected with the Zika virus during the three weeks of the Olympics is very low.

Rio de Janeiro 2016: a dry winter and low temperatures should reduce the transmission of dengue and Zika

Léo Ramos Rio de Janeiro 2016: a dry winter and low temperatures should reduce the transmission of dengue and ZikaLéo Ramos

Only 15 cases
If the expected 500,000 tourists really come to Rio de Janeiro, probably only 15 will be infected by a mosquito with Zika, and of those only three will exhibit symptoms, according to projections made by Massad, Coutinho and two other collaborators, Dr. Marcelo Burattini and physicist Raphael Ximenes, and presented in a letter published in The Lancet. Yet the risk of dengue is 17 times greater. If the calculations are correct, about 250 visitors will be infected and 50 will present dengue symptoms. Massad is one of the lead researchers of the Zika Plan, a European Zika virus research network, and he calculated the risk of dengue infection for tourists during the 2014 World Cup. He and his group reached those numbers with regard to Zika infection by taking into account the estimated number of cases that have already occurred in Brazil (about 1.5 million), the dynamics of dengue in Rio de Janeiro in the years of the most serious epidemic, and what is already known about the behavior of Aedes aegypti, the mosquito that transmits the two diseases. “The individual risk of Zika infection is very low, but everyone has to make their own decision as to whether or not to attend the games,” says Coutinho. “Athletes should protect themselves by using insect repellent, because the price of getting sick could be very high.”

“There is no public health reason to cancel or postpone the Olympics,” Dr. Thomas Frieden, director of the Centers for Disease Control (CDC) in the United States, told the press. An influx of 500,000 tourists to Rio de Janeiro represents only 0.25% of the 200 million international trips that routinely take place in regions with Zika and contribute little to spread the Brazilian virus to other countries, American epidemiologists concluded.

These arguments have not changed the opinion of Attaran and his colleagues. In a memo sent by e-mail to FAPESP, and according to Attaran also to WHO, the group refutes all the arguments that the risks are low, that the model’s results are unreliable because there is little accurate data on Zika, and they estimate that participation in the event will contribute to the emergence of up to 10 new transmission outbreaks in other countries.

“The games will not be postponed or canceled, but this is unfortunate, since they could be held at another time, with less danger, fear and disorganization,” Caplan said. On one point, all sides of the debate agree: pregnant women or women who want to become pregnant should not go to Rio de Janeiro. If their partners do attend the games, they should not have sex without protection for at least six months.

Risk of dengue for tourists in Brazil during FIFA World Cup 2014 and Olympic Games-Rio 2016, using mathematical modeling (nº 2012/18463-4); Grant Mechanism Fast-track Doctorate; Recipient: Raphael Ximenes; Principal Investigator Eduardo Massad (FM-USP); Investment R$116,689.66.

Scientific articles
MASSAD, E.; COUTINHO, F.A. WILDER-Smith, A. Is Zika a substantial risk for visitors to the Rio de Janeiro Olympic Games? The Lancet. June 17, 2016.
CODECO, C. et al. Zika is not a reason for missing the Olympic Games in Rio de Janeiro: Response to the open letter of Dr. Attaran and colleagues to Dr. Margaret Chan, Director-General, WHO, on the Zika threat to the Olympic and Paralympic Games. Memórias do Instituto Oswaldo Cruz. June 2016.