Photos from the Trump-Biden debate show just how close America was to having 2 infected presidential candidates

• Democratic presidential nominee Joe Biden tested negative for COVID-19 on Friday, hours after President Donald Trump announced he and First Lady Melania Trump tested positive for the virus.
• Cleveland Clinic, which worked as a health adviser for the Commission on Presidential Debates for Tuesday's debate between Biden and Trump told Insider there was a "low risk of exposure" to the event.
• But the risk wasn't zero — it's unclear exactly when Trump and Melania Trump were first exposed to COVID-19.
• Photos show Melania Trump walking closely to Biden on stage while not wearing a mask, and speaking loudly indoors may have led to a higher risk for virus particles to linger in the air.

President Donald Trump announced on Friday that he and First Lady Melania Trump tested positive for COVID-19, just days after he participated in an in-person debate against Democratic nominee Joe Biden in Cleveland, Ohio.

Photos from the debate show Trump and Biden maintained their distance throughout the event — but Melania Trump was pictured walking close the former vice president on stage while not wearing a mask, and that coupled with the risk of transmission during indoor events, reveals just how close the US came to having two presidential candidates contract COVID-19.

The Cleveland Clinic, which worked as a health adviser for the Commission on Presidential Debates during the event, told Insider that it put multiple safety measures in place to prevent the spread of COVID-19 at the debate, and confirmed everyone attending had tested negative prior to entry.

"Individuals traveling with both candidates, including the candidates themselves, had been tested and tested negative by their respective campaigns," the Cleveland Clinic said. "Based on what we know about the virus and the safety measures we had in place, we believe there is low risk of exposure to our guests."

Debate moderator Chris Wallace said on Fox News on Friday that there was an "honor system" for candidates to confirm they were tested for COVID-19, though that has not been confirmed by the Cleveland Clinic.

While the Cleveland Clinic said there was "low risk of exposure" to the virus at the debate, the risk of exposure wasn't zero.

It's unclear exactly when or how the Trumps contracted COVID-19. It can take four to five days between exposure and symptoms to start, and top White House aide Hope Hicks — who had been in close contact with the president — announced she was positive hours before the president announced his diagnosis.

The World Health Organization said that being indoors can allow the virus to linger in the air through small particles called aerosols, and research suggests that loud talking can propel particles even further.

Biden and Trump spoke loudly throughout the debate and there's a chance Biden could have been exposed to COVID-19 if the president and First Lady had already contracted the virus prior to the event — and medical experts told Business Insider it was likely they did.

As for Melania Trump walking closely to Biden, it's unclear exactly how far Biden's podium was from the steps Melania Trump walked up to get on stage, but Insider estimates between five and 10 feet. Neither the Huntington Convention Center, where the event was held, nor Commission on Presidential Debates immediately responded to Insider's requests for further information.

Business Insider reporter Anna Medaris Miller reported that Biden will likely have to take another COVID-19 test, since it's only been two days since he shared the debate stage with Trump.

Amesh Adalja, a Senior Scholar at the Johns Hopkins University Center for Health Security, told Business Insider that more details need to be known before it's determined if Biden was exposed or not.

"Knowing the timeline of the president's last negative test ad when he became symptomatic and when the positive test was resulted — knowing that timeline is the only way you can really determine whether or not Joe Biden was a significant exposure," he told Insider.