Some people seem to have a fundamental misunderstanding about bacteria and viruses.
They think that things like soil, mud, animal skin dander etc from working with animals (especially horses or rabbits or pastoral animals when the only food they eat is grass or hay,) is the “dirt” you eat which makes you ill or eventually immune to “bacteria.” This just isn’t true. Of course you’ve very rarely been ill from mucking out a stable or digging in the soil or your child has a hefty constitution from eating half a worm. Rarely, can you pick up a bacterial infection from something like that - you would literally have to lick the horse shit off your fingers, and i’m guessing that most of the people who believe that would not do that if their hands were visibly soiled.
The places which make you ill are door nobs, taps, remote controls, light switches, bannisters, phone screens, people who are ill preparing food for you, shared toys in public places, care environments like hospitals, nursing homes and nurseries, public toilets with no washing facilities, going into someone’s home who has been ill. And not washing hands after all of the above.
These places occasionally make you ill with viruses like colds, flu and stomach bugs, if you don’t wash your hands.
While we can become immune to some viruses, there are so many different strains of the common cold and flu, it’s a lottery whether you’ve just caught the one you’ve previously had and are therefore immune.
90% of gastroenteritis is norovirus. You cannot become immune to norovirus. The immunity period is 14 weeks. If you catch it in 2017 you can still get it in 2018. There are some people who never get norovirus or are asymptomatic carriers, and they are the 20% of the population who are “non secretors.”
Norovirus or flu can kil someone with a compromised immune system.
That’s why to avoid getting ill or making vulnerable people ill, others should simply wash their hands.