My grandma always used to wash undies by hand separately and then pour boiling water over them. I found it to be very weird when I was a kid, but she might have been onto something. I would do this if I was living with an immunocompromised person but its probably overkill for a healthy family.

It's also suggested you clean the washer every once in a while too.

Fecal bacteria is found everywhere it seems, so that's why frequent hand washing (especially before food prep) is important.