If there is such a disparity, presumably that will show up in the health stats? They mention a few viruses transmissable in this way, so if their numbers and t

If there is such a disparity, presumably that will show up in the health stats? They mention a few viruses transmissable in this way, so if their numbers and their inferences stand up, we should see a huge difference in the number of cases (or speed of communication - I'm not sure which - I am not an epidemiologist) between the London and Newcastle? If such a difference doesn't show up, either their methodology was bogus, their inferences wrong (these viruses can't be usefully transmitted in this way) or it doesn't matter because some other factor balances it (maybe greater exposure to these bugs causes a degree of resistance).