The International Olympic Committee said Sunday that it will order tests to check for viruses in Rio de Janeiro’s water bodies. Brazil's second-largest city is under pressure to meet the IOC's standards as it prepares to host the 2016 Summer Olympics.

The IOC and local organizers had previously said that they would only test for bacteria in the water, according to established standards in Brazil and most other nations, while examining the safety of recreational waters. However, the testing standards were raised after an Associated Press investigation last week found high levels of viral contaminants from human sewage that placed athletes at risk of falling violently sick. Several competitors training in Rio have already caught fevers, vomiting and diarrhea.

The AP conducted four rounds of testing in each of the three water venues where 1,400 participating athletes are set to compete. The results found that none of the Olympic venues were safe for swimming or boating, and that athletes who ingest just three teaspoons of water have a 99 percent chance of contracting a viral infection. The viral concentrations found in all the samples were roughly equivalent to the levels found in raw sewage.

Brazilian officials have assured competitors and authorities that the water will be safe by the time the competitions begin in August 2016. However, previous tests only looked for bacteria and ignored viruses, prompting the IOC to change its decision after an advisory from the World Health Organization that it should conduct more tests.

“The WHO is saying they are recommending viral testing,” IOC medical director Dr. Richard Budgett said, according to the AP. “We’ve always said we will follow the expert advice, so we will now be asking the appropriate authorities in Rio to follow the expert advice which is for viral testing. We have to follow the best expert advice.”

The IOC’s decision came after the International Sailing Federation (ISAF) said Saturday that it would conduct independent virus tests.

“We’re going to find someone who can do the testing for us that can safely cover what we need to know from a virus perspective as well as the bacteria perspective,” Peter Sowrey, CEO of ISAF, reportedly said. “That’s my plan.”

However, athletes and organizers shrugged off health concerns at a Saturday event when several para-athletes dipped into the waters off Copacabana beach. The waters will be used for triathlon, ocean swimming and sailing events during the games.

Rio de Janeiro was awarded the games in 2009, and the city promised to clean its waters permanently as part of its Olympic legacy, but Mayor Eduardo Paes has acknowledged that this will not be done, calling it a “lost opportunity.”