That rather speaks against it being a microbiome - it could just be incidental contamination the body is in the process of cleaning up. To be a microbiome I would expect to a diverse, well-adapted quorum of species that find some type of symbioses.

Absent that evidence, well biology is probability - something is always happening somewhere just by chance and statistics, but it doesn't make it a feature.

Aren’t viruses much harder to detect than bacteria? Viruses are generally smaller and are completely inert without a host cell. Bacteria, besides be larger, also have their own metabolic processes and distinct structures you can do things like grow them in a laboratory culture until the colony is much obvious.

Your comment makes it sound like bacteria are harder to detect but if we’re already identifying viruses, locating bacteria seems easier.

(Though some viruses are bigger than the smallest bacteria, like Mycoplasma at 200nm, viruses are generally smaller)

Both are hard to detect if there are only hundreds of them amongst trillions of human cells.

At that point, 'just look with a good microscope' becomes infeasible, and you end up needing biological tricks like DNA amplification.

And it makes me wonder how much we’re still missing or overlooking in the microbial landscape of our own bodies.