It is one person going against all the official medical sources, note he himself is not medically qualified (but may be expert on filtration). BBC TV news interviewed woman who had had an illness after travelling; and had been told by Doctor that such illnesses were common after travel, more likely that she picked up infection whilst on holiday - far greater exposure to unfamiliar illnesses. If you consider areas where TB (for example) is endemic, the locals who fly with you are those least likely to be infected.