Hamblin: The focus on how this virus spreads has shifted from surfaces to airborne, aerosolized transmission in terms of how important we think things are.
Wells: Which is why we’re very much focused on being outside when gathering right now as reopenings are happening, because the air is moving around a lot more?
Hamblin: Right. If I could use a weird metaphor: When you’re outside, if you cough, it’s sort of like peeing into a river, as opposed to if you’re in a room that’s not well ventilated, it’s like peeing in a hot tub. Ideally, you would do neither, but one of them is definitely worse. The virus aerosolizes, obviously, when someone is coughing and yelling and singing, but also it can come out in things called toilet plumes.
Wells: What is a toilet plume?
Hamblin: So when you flush the toilet, not everything goes down. Some small portion of what was in that bowl gets misted into the air. This is all hypothetical right now, but we know that people shed virus in their feces, sometimes for long periods after they’re no longer even sick.
Wells: Wait, so people who are fully recovered can continue to shed contagious virus through their feces long after they’re recovered?
Hamblin: There is one key word in there you said, which is contagious. We don’t know exactly the dose of virus that you’d need to be exposed to in order to get sick. It’s very unlikely that there would be enough virus from inhaling someone’s toilet plume one time for anyone to get sick.
Wells: Does this mean that shared public restrooms, even if no one is in them while you’re using them, are dangerous?
Hamblin: Well, the answer that I came down with is they’re dangerous if they’re not properly ventilated. It’s exactly for reasons like this that commercial buildings are supposed to have exhaust fans that are constantly running that are pulling air out of the bathroom and blowing it out outside.
Wells: Exhaust fans, ventilation, the filtration system on the building—those are the things that clear the virus?
Hamblin: Yeah. In restrooms, specifically, because we know about toilet flushing, because we know it’s just full of infectious particles of various sorts, so you’re supposed to have a ventilation fan running in there constantly. Even if there is a toilet plume, it’s not hanging out there very long. We should assume that that’s safe.
Where it could be an issue is if that wasn’t working and, obviously, toilets aren’t the only way we aerosolize this virus. And when you have air-conditioning going, you’re basically recirculating a lot of air. So when you recirculate that air, it goes through a filter. There are some filters that are good enough to catch this virus and remove it while it’s being recirculated. In that building you’re much safer than if you’re in a building that is running air-conditioning and hasn’t upgraded its filters appropriately, doesn’t have the best kinds of filters, or doesn’t have a system that can handle those high-quality filters.