How is that you yourself know about the Germ Theory of disease? Because you learned about it in health class in school, or your parents told you. Mexican immigrants didn't have those classes, or those parents. How would they know?
Bad worker hygiene in agriculture is caused by mass immigration's effect on the labor force. N.B. Nothing about this situation would be improved by legalization or guest worker programs.
I suppose that means the USDA is going to go around conducting classes in hygiene in Spanish,. Of course they'll also need to hire Mixtec speakers for the 100,000 illiterate Indians now living in California. As Steve Sailer said
Because wages are so low, there's little need to mechanize farm work in California. And because the state's farm work jobs are so poorly paid for the brutal conditions (three workers died of heat stroke this summer), nobody makes a career out of it if they can. So, the growers constantly suck in to this country more (and ever less educated) illegal aliens. Cooper notes:
"In a pattern that one academic calls “ethnic replacement,” succeeding waves of ever poorer, more marginal Mexicans, many of them from indigenous communities where Spanish is a foreign language, increasingly constitute the field labor force. The downward-spiraling Mexican economy feverishly churns those waves to the degree that, at any moment, as many as 20 percent of California’s agricultural workers have been in the U.S. for less than a year." The neocon open border cheerleaders contend that these newcomers will "assimilate" into American culture. Real Soon Now. Yet, these Mixtec-speaking Indians who increasingly make up California's farm workers haven't even assimilated into Hispanic culture in the 484 years since the Spaniards conquered Mexico.
There are two obvious things that would make the food industry more sanitary: English speaking, American-educated employees, and machine picking. These would reduce the other social costs associated with immigrant farm labor, too.