Looks like ~60% of the population has a genetic immune deficiency then ....
"In 2013, the Pharmaceutical Benefits Scheme (PBS) and Repatriation Pharmaceutical Benefits Scheme (RPBS) supplied 29.2 million prescriptions for antibiotics to over 10 million unique patients (45 per cent of the Australian population).12 While PBS and RPBS data provide a useful indicator, the true level of total antibiotic usage in humans in Australia is much higher as these figures do not capture hospital use or private prescriptions in the community."
An average of three courses per person, per year, for a minimum of 45% of the population. No surprise that resistance is building.
