I know hospitals try to wash their stuff thoroughly, at high temperatures, because of hygiene issues. Good for them.
Every now and then, one should do that at home. Clean the machine thoroughly.
I heard a lecture some years ago by Hans-Curt Flemming who worked on biofilms. He dissected and analysed his own washing machine and provided slides. And an analysis of several biofilms on several parts of the machine.
It wasn’t just not pretty, it was amazingly gross. I can’t remember if he did show research to prove the statement, but he was quite clear in his assessment that using a biofilm-infested washing machine is a great way to spread disease (e.g., in a family). Interestingly, he even mentioned the different common cold viruses which IMO shouldn’t be able to infect anyone after a surfactant treatment. He advised to have a 90°C cleaning run at least every two months, and with bleach. Also separate clothes if someone in the family is sick. Additionaly, reduce the amount of laundry detergent, as the biofilms live of the residues.
(Fast forward several years, when I was living in Switzerland. TIL: if you rent a flat in any building with more parties, you very often get a timeslot to use the communal washing machine in the basement. Basically no-one I knew had a washing machine in their apartment…)
Another thing he had in his lecture was a strange case of hospital hygiene. Long story and forensical detective work short: germ count after cleaning in some parts of the hospital was consistently higher than before, and it turned out that there was a biofilm in the pipes delivering the desinfectant within the whole hospital, and which would only come loose and be distributed by cleaning staff at a certain pressure or velocity, i.e. only in a specific part of the building under specific circumstances (like opening the valve fully or something like this, can’t remember properly). They found out after they had tried to fire several cleaners who insisted on doing everything by the book, and then did prove to the hygiene medical staff that they, indeed, did everything by the book.
I, for one, steer clear of washing machines I don’t own, and clean. I invested in a Miele for my family some years ago, and I think it already paid off, including environmentally. Only wash when really needed, cool cycle, but adding a cleaning cycle every now and then (whenever the drain pump shows a yucky biofilm).