Daniel BuenoOf the 600,000 foreign tourists expected for the World Cup, it is anticipated that about 100 could contract dengue fever during their stay in Brazil. However, the risk varies significantly from one host city to another. In São Paulo and other host cities in the South and Southeast, the danger is minimal because cases of the disease plummet during the winter months when temperatures are lower and there is less rain—two factors that promote the spread of the Aedes aegypti. Fans in Salvador, Fortaleza, Natal, Manaus and Recife will face a statistically higher risk. The city that may register the largest number of cases is Rio de Janeiro. Although the majority of cases tend to occur between February and May, the capital city of Rio de Janeiro State is expected to draw more tourists and for a longer period than the others.
This assessment is in an article submitted to the journal Lancet Infectious Diseases by a group led by Eduardo Massad, professor at the University of São Paulo School of Medicine. Massad specializes in mathematical models that assess the spread of diseases. Other authors of the article include researchers from USP, Unifesp, the Oswaldo Cruz Foundation, the Lee Kong Chian School of Medicine of Singapore and authorities from the Brazilian Ministry of Health.
The study was performed as a result of the recently released generic assessments of a perceived exaggeration of the risk for tourists, such as one published in December in the journal Nature by Simon Hay of Oxford University. In this article, the author calculated the percentage of cases that had occurred in June and July during the period from 2001 to 2013 compared to the annual total in each World Cup city during this time frame. The article, which referred to this as the “percentage of annual case burden experienced,” was apparently identified as the likelihood that visitors to these cities would contract dengue. This identification, Eduardo Massad observes, is inaccurate.
According to the Brazilian authors, the Hay article is apparently being used by consulates, travel agencies and other foreign organizations to alert visitors that “football fever could be a dose of dengue,” as the title of the article in Nature indicates. In the same article, Hay writes that “World Cup fans in Brazil may be exposed to a nasty and incurable tropical disease.”
“Since calculation of the risk is incomplete, and since dengue is not ‘incurable,’ the author was irresponsible in publishing this article, which looks like propaganda against holding the games,” Massad says.
Due to the seriousness of the statements, the authors of the Brazilian article used a detailed algorithm to estimate the hypothetical risk any tourist visiting Brazil during the World Cup faces for contracting the disease based on the chosen itinerary. Thus, for example, for a tourist who decides to spend the World Cup period traveling as follows: São Paulo (three days); Fortaleza (six days); Brasília (five days); Belo Horizonte (five days); Fortaleza (six more days); and Rio (eight days), the estimated individual risk will be about 0.05%, well below the alleged “burden” of between 0.2% and 13.5% as stated in the Hay article.
Brazilian researchers warn that the risk may be overestimated since foreign tourists are generally less exposed to mosquito bites than residents of Brazil. One of the findings of Massad and his colleagues is that the intense flow of tourists during the World Cup may in fact take dengue to other countries, as is the case wherever there is an endemic infectious disease. “After all, anyone who visits certain places in Canada in the summer may contract and export West Nile fever,” Massad says. To minimize this risk of exporting the disease, the authors say that tourists who contract dengue should not return home while they are ill; rather, they should be treated in Brazil, where the health system has experience with this problem, and return once they are better. “It is also worthwhile to point out that the incidence of dengue varies from year to year and, judging by the data recorded to date, the incidence in 2014 is similar to that of years with a lower occurrence of dengue in the last 10 years,” Massad states. “Finally, it is surprising that Nature published an article that says that if you are out in the rain you may get wet…”.
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