Twenty-three top Chinese swimmers tested positive for the same powerful banned substance seven months before the Tokyo Olympic Games in 2021 but were allowed to escape public scrutiny and continue to compete after top Chinese officials secretly cleared them of doping and the global authority charged with policing drugs in sports chose not to intervene.

Several of the athletes who tested positive — including nearly half of the swimming team that China sent to the Tokyo Games — went on to win medals, including three golds. Many still compete for China and several, including two-time gold medalist Zhang Yufei, are expected to contend for medals again at this year’s Summer Games in Paris.

China acknowledged the positive tests in a report by its antidoping regulator, saying the swimmers had ingested the banned substance unwittingly and in tiny amounts, and that no action against them was warranted.

But an examination by The New York Times found that the previously unreported episode sharply divided the antidoping world, where China’s record has long been a flashpoint. U.S. officials and other experts said the swimmers should have been suspended or publicly identified pending further investigation, and they suggested that the failure to do so rested with Chinese sports officials; swimming’s international governing body, World Aquatics; and the World Anti-Doping Agency, the global authority that oversees national drug-testing programs.

Those authorities decided not to act despite an email exchange between a Chinese antidoping official and a top world swimming official appearing to indicate that a violation may have taken place and would, at the least, have to be publicly acknowledged.

Even after other national and international antidoping officials repeatedly provided the global regulator, known as WADA, with intelligence suggesting a cover-up and doping by Chinese swimmers, the agency chose not to try to hold the athletes accountable, asserting “a lack of any credible evidence” to challenge China’s version of events. WADA defended its decision not to take action, calling the criticism unsubstantiated.

The FBI learned in the past year about the positive tests, the Chinese rationale for clearing the athletes of wrongdoing, and the inaction by WADA, according to two people familiar with the matter and a document examined by the Times.

This article is based on a review of confidential documents and emails — including a report compiled by the Chinese antidoping agency and submitted to WADA — and interviews with people involved in antidoping efforts around the world. Some interviews were conducted on the basis that sources not be identified because they were not authorized to speak publicly or had concerns about retaliation.

Experts in antidoping, drug-testing and compliance interviewed by the Times said the handling of the case of the Chinese swimmers and the lack of disclosure about the positive tests ran counter to long-established precedents meant to ensure transparency, accountability and competitive fairness in elite sports.

The episode also exposes shortcomings in the system set up to police doping in sports, with one of the world’s most powerful countries able to send athletes who had recently tested positive for a banned drug to the world’s most high-profile athletic competition, where they set world and Olympic records without any public disclosure.

An investigation by the Chinese antidoping agency, known as Chinada, suggested that the incident stemmed from a tainted food supply, a finding that some experts considered implausible.

In their report, Chinese investigators described how many of the country’s best swimmers were staying at the same hotel for a domestic meet in the final days of 2020 and the first days of 2021. Two months after the swimmers tested positive for the banned substance — a prescription heart drug that can enhance performance — Chinese investigators reported finding trace amounts of the substance in the hotel’s kitchen.

Their report offered no evidence of how the drug got there, despite enlisting the help of China’s national police. But they concluded that the swimmers had unwittingly ingested it in small amounts.

WADA confirmed in a statement that it had “carefully reviewed the decision” made by the Chinese and chose not to act after consulting scientists and external legal counsel “to thoroughly test the contamination theory presented by Chinada.”

“Ultimately, we concluded that there was no concrete basis to challenge the asserted contamination,” WADA’s senior director of science and medicine, Olivier Rabin, said in the statement.

In contrast to WADA’s position, the International Testing Agency, a group based in Switzerland that was created after an earlier Russian doping scandal to provide an extra layer of independent oversight for global athletic competition, said its own assessment of the case remains ongoing.

Chinada said in a statement that it determined its athletes had not violated any antidoping laws and therefore it was not obliged to publish any details related to the case without the athletes’ consent.

The Chinese Swimming Association did not reply to a fax seeking comment on the tests.

Swimming’s governing body confirmed the cases had been reviewed by a doping control board and been subjected to independent expert scrutiny, without providing further details. “World Aquatics is confident that these AAFs were handled diligently and professionally, and in accordance with all applicable antidoping regulations, including the World Anti-Doping Code,” it said, referring to adverse analytical findings, the term for positive tests.

The story that the swimmers had ingested the substance unknowingly provided a rationale for Chinese authorities to break with normal antidoping protocols. Those would typically involve a public declaration that the athletes in question were being temporarily suspended pending further investigation, particularly if a finding of food contamination had not yet been established.

The handling of the matter by Chinese authorities and global regulators came at an especially sensitive moment. The swimmers were planning to compete in just a few months at the Summer Games in Tokyo, and China, battered by the pandemic, was to host the Winter Games the following year.

The Olympic Games are a point of pride for the Chinese government, as a way to project the country’s strength and competence. In recent years China has focused in particular on sports — marquee ones like swimming, but also minor ones like women’s weightlifting — where it can collect medals in bulk.

The story of the positive tests began unfolding a year into the coronavirus pandemic, a period when antidoping authorities feared that travel bans and closed borders in many countries would make it easier to cheat. Those restrictions would reduce the opportunities for testing at international events and lead to an almost total reliance on national antidoping agencies.

The roughly two dozen positive tests involving Chinese swimmers were collected at a New Year’s event held over four days in December 2020 and January 2021 in Shijiazhuang, a provincial city of about 11 million people a few hours southwest of Beijing.

Ultimately, according to the 61-page investigative report compiled by Chinada and reviewed by the Times, a total of 60 tests were conducted on 39 swimmers. Those urine samples produced 28 positives involving 23 of the meet’s competitors — a shockingly high failure rate. All of the samples tested positive for the same drug, trimetazidine, known as TMZ.

TMZ is a prescription medication designed to help people with heart disease. It is included in a category of performance-enhancing drugs that come with the harshest penalties. It can help athletes increase stamina and endurance and hasten recovery times, and is difficult to detect because it quickly clears through the body.

The final report by the Chinese said investigators had discovered traces of TMZ in sink drains, spice containers and cooktop vents in the kitchen of the Huayang Holiday Hotel in Shijiazhuang, where most of the swimmers and coaches at the meet had stayed.

There is also evidence that the Chinese antidoping authorities knew on March 15, 2021, the day they reported the positive tests, that they faced the possibility of having to publicly disclose the names of the swimmers. That day, the top legal official at Chinada wrote an email to her counterpart at the world swimming association that an “initial review and preliminary investigation shows that these are not normal” positive tests.

Emails obtained by the Times show that by April 2021, at least two of WADA’s top officials — the most senior executive at the agency and its top legal officer — had been informed that the Chinese swimmers had tested positive.

In their report, filed in June 2021, Chinese investigators ruled out contaminated supplements or sabotage as reasons for the positive tests. They offered no explanation, however, for how a prescription drug available only in pill form had contaminated an entire kitchen.

WADA said “the contamination scenario was further supported” by the low concentrations of the drug and the fluctuation of test results between positive and negative.

The Chinese pointed to low concentrations of TMZ in the urine samples to conclude intentional doping was “impossible.”

That claim was rejected by five independent experts who discussed the matter with the Times. The low concentrations, they said, could just as easily have meant the athletes had been at the end of the excretion period for the drug.

The New York Times News Service