People attending the 2016 Summer Olympic games in Rio de Janeiro stand a low risk of contracting or spreading the Zika virus, says a new report in the Annals of Internal Medicine.

Attendance at the Rio Olympics is estimated to be between 350,000 and 500,000, according to the report – written by Albert I. Ko, MD, of Yale University in New Haven, Conn. and his colleagues – and in the worst-case scenario, the projected likelihood of infection will be between 1 in 56,300 and 1 in 6,200. This means that, at most, 80 people attending the games will contract the Zika virus (95% confidence interval, 63-98), while the lower bound of the estimate is a mere 6 individuals (95% CI, 2-12). Furthermore, only 1-16 individuals (95% CI, 0-4 and 9-24, respectively) of infected individuals are expected to be symptomatic (Ann Intern Med. 2016 Jul 26. doi: 10.7326/M16-1628 ).

Data from the 2014 FIFA World Cup tournament – which also took place in Brazil – estimates that 53.3% of attendees will come from one of eight countries or regions: United States, Canada, Europe, Oceania, Japan, South Korea, and Israel, all of which are locations where mosquito-borne disease transmission rates are expected to be low. Individuals who contract Zika virus and take it back home with them are expected to number between 3 (95% CI, 0-7) and 37 (95% CI, 25-49), mainly because the Zika virus is only expected to take 9.9 days to naturally clear any infected individual.

“Most of the remaining travelers (30.2% of the total) are expected to return to Latin American countries already experiencing autochthonous ZIKV transmission, contributing 9.0 (0.0 to 29.7) to 116.0 (59.4 to 188.1) additional person-days of viremia,” the report states. “This effect is negligible relative to prevalent infections caused by ongoing transmission in these countries.”

Recently, the U.S. Centers for Disease Control and Prevention also announced that chances of acquiring the Zika virus are low for those attending the 2016 Summer Olympics, and that only individuals from a small number of countries have any real danger of introducing the disease into a previously unaffected and potentially dangerous climate.

Sexual transmission of Zika virus remains a risk, however, the Annals report notes. People are urged to use condoms or abstain from sex during the Olympics in order to mitigate the risk of spreading the disease. Additionally, women who attend the games are best advised to delay getting pregnant for several weeks, if not months, after returning home. Women who are already pregnant should not attend the games, and everyone who attends the Olympics should wear mosquito repellent, long-sleeve shirts and pants, and use either a fan or a mosquito net in their hotel rooms to avoid getting bitten.

Dr. Ko and his coauthors declared no conflicts of interest.


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