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Max, a psychiatric doctor from North-West England, recently found out he's already had coronavirus.
Several months ago he lost his sense of taste and smell, however back then these were not seen as official symptoms of the virus.
So because he didn't have a cough or temperature, he "followed the rules, went back to work and wasn't offered a test".
This meant the 27-year-old came into contact with up to 100 patients a week.
"It's not anybody's fault. It's just what happens when there's a new disease that we don't know enough about - we still don't know enough about it," he tells Radio 1 Newsbeat.
"I feel very guilty, I was walking into wards that we thought were coronavirus free and I would have been bringing it to them."
Max recently took the antibody test, which told him he'd already had the virus and could indicate increased immunity.
As part of his job, Max provides mental health support to hospital patients who have had surgery or been in an intensive care unit (ICU).
"We are seeing lots of Covid-19 patients from a mental health perspective, particularly after they've been in ICU, it's obviously a very big thing to have gone through.
To support patients, Max says he needs to be in close proximity to communicate.
Even though he didn't realise it was coronavirus, he says his symptoms were striking.
"I've never experienced anything quite like it before.
"I think all of us probably lose our sense of smell and taste a little bit when we have a cold, but this was complete, I couldn't even smell coffee or taste the strongest things like vinegar - nothing."
He thinks stricter rules around personal protective equipment (PPE) such as masks, gloves and gowns could have prevented him from spreading the virus.
"It was quite late that we moved to using PPE for all interactions, and it still isn't used in general spaces within hospitals, so in offices and things, we're not wearing masks."
WHO guidelines, currently recommend health staff wear a full gown and visor.
"I think bringing in PPE for all interactions with patients earlier would have been safer and also rolling out PPE more widely in spaces where it's impossible to socially distance would have helped reduce the risk.
"It's obviously not nice to feel like you're the first person that could be bringing it into an area or bringing it into a hospital even.
"I don't know for certain how many patients, if any, I passed this on to, but the chance that I could have done is worrying.
The loss of smell and taste have since been added to the UK's list of symptoms.
Max went on to tell Newsbeat there is still more to learn about the virus from a mental health perspective.
"There may also be something about this virus itself, which makes people delirious, so see things, hear things, or get more confused than other illnesses, but we just don't know enough about it yet."