Pasteurization was started in the first couple of decades of the last century. My grandfather was a microbiologist who worked with Emil Berliner [the man who invented the Victrola flat record] to get pasteurization laws in place. By the way, granddad died from TB (as did my father) from being infected through his research. There weren’t many test for the disease in cattle or people back then. I don’t know what it’s like today.
TB is coming back in hard-to-treat forms, but it is no way as wide spread [yet] as it was at the beginning of the last century. Kids died from all sorts of diseases then that are largely forgotten now thanks to modern science and public-health efforts: TB, typhoid, typhus, diphtheria, rheumatic fever, blood poisoning, polio and so on.
When we had cows, I remember straining the milk through cloth to filter out the small pieces of cow shit and other dirt. I don’t know what they do nowadays in large dairies. I guess it’s all mechanized.
And you have to look at why it was needed. Large groups of cattle huddled together in large feedlots. This was not so common prior to the turn of the 20th century.