There’s an interesting article in the CBC, where journalists took a set of flights, swabbed surfaces, and worked with a microbiologist to culture their samples.
What they found will shock you!
Well, airplanes are filthy. Not really shocking. What was surprising to me was that the dirtiest of the surfaces they tested was the headrest. (They did not test the armrests.) Also, the seat pocket is a nice incubator and rarely cleaned. Not all that surprising, but I hadn’t considered it.