This is one of the things that I like about the expanse series. When people first start moving out to alien ecosystems, they specifically go into how alien viruses etc are probably not going to be a problem. The metaphor they use is "mining" basically. Where they're not concerned that people will get infected, but they're concerned that some organism will find out that people are full of some resource that the organism can use.
And in fact they bump into some sort of algae that lives in the atmosphere that really likes the saline mixture that makes up most of the liquid in our bodies.
I’ve never heard of the Expanse series but your mining comment is both terrifying and intriguing! DuckDuckGo tells me it’s both a series of novels and a Syfy TV series - I’m curious which one (or perhaps both?) you’re referring to so I can add it to my read and/or watch list.
And in fact they bump into some sort of algae that lives in the atmosphere that really likes the saline mixture that makes up most of the liquid in our bodies.