(CNN) A congressman on Friday called for the Securities and Exchange Commission to investigate the leak of a video showing physicians at the University of Chicago speaking enthusiastically about an experimental drug to treat Covid-19.

Texas Democrat Rep. Lloyd Doggett, chair of the House Ways and Means Health Subcommittee, said the leak was "so significant" at a time when the world is "so desperate to find a cure."

University of Chicago physicians are helping test remdesivir, an antiviral drug made by Gilead Sciences in patients with Covid-19.

Dr. Kathleen Mullane, an infectious disease specialist at the University of Chicago, is leading the clinical trial funded by Gilead.

"The best news is that most of our patients have already been discharged, which is great. We've only had two patients perish," Mullane is quoted as saying in the video.

The video was leaked to STAT News, a health news website, which published it Thursday afternoon. The story was picked up widely by other news outlets, including CNN, and Gilead stock soared 12%.

Doggett, an attorney, noted that "providing information that's designed to impact the stock market is not something that is permitted under federal securities law."

He said it's not clear where the leak came from. "That's why we need a thorough SEC investigation," he said.

A Gilead spokesman Chris Ridley said his company was not involved in the leak.

"Gilead had nothing to do with the information sourced by STAT from an internal recording out of the University of Chicago hospital," Ridley wrote to CNN in an email.

Effect of remdesivir unclear

A spokesman for the SEC declined to comment. A spokeswoman from the University of Chicago did not respond to a request from CNN for comment.

The University of Chicago is conducting two remdesivir trials being paid for by Gilead: one in patients with severe symptoms and the other in patients with moderate symptoms.

"Most of our patients are severe and most of them are leaving at six days, so that tells us duration of therapy doesn't have to be 10 days," Mullane was quoted in the STAT article as saying in the video.

The Gilead trial for patients who are severely ill does not include what's known as a control group, so it could be difficult to say whether the drug is truly helping patients recover better. With a control arm, some patients do not receive the drug being tested so that doctors can determine whether it's the drug that is really affecting their condition.

The company's trial for moderately ill Covid-19 patients does have a control group.

There's a separate large trial of remdesivir sponsored by the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health, which does include a control group.

Dr. Kathryn Hibbert, director of the medical intensive care unit at Massachusetts General Hospital, is participating in the NIAID trial. She said it's not at all clear to her if the drug is having an impact.

"We have seen patients who've received remdesivir who've had remarkable recoveries and we've seen patients who've not received remdesivir and had remarkable recoveries," said Hibbert, also an instructor at Harvard Medical School. "Overall, patients are doing well and have made recoveries, even the sickest of the sick."

Doctors 'need to question their assumptions'

Since most patients recover from Covid-19, she said, physicians need to be careful before they ascribe a patient's improvement to any particular treatment.

"As human beings, we are so conditioned to tie an intervention with outcomes and establish a causal relationship between those two things," she said. "I change a patient's meds and the next day they look better, and it could be because I changed their meds, or it could be they were destined to get better anyways for other reasons."

She added that doctors need to question their assumptions.

"Our gut feeling is so influenced by what's in front of us and the last patient we treated that it's pretty dangerous to make decisions based on that gut feeling," she said. "The whole reason to run trials is our guts are notoriously misleading. That's the entire rationale for a science and evidence-based approach."

Hibbert said it will take weeks or months to get results and doctors and patients will need to wait for the results of the clinical trials before knowing which Covid-19 patients -- if any -- should be getting remdesivir.

"I think we should be extremely cautious about responding too enthusiastically to early data that has not been thoroughly vetted," Hibbert said. "In the scientific community, over decades, we've established that critical review of clinical trials is the best way to determine if the data is strong enough to inform clinical decisions."