Typhoid Pursey. Your purse could be carrying all kinds of nastiness including E. coli.
"A microbiologist who examined the samples taken from 50 purses recommended women wash the outside of their handbags at least once a day with soap and water to help remove any lurking contaminations. Clorox wipes will also work to remove germs.
While one might be tempted to regard the caution about bacteria-harboring handbags as being of interest to women only, members of the non-purse-slinging public (i.e., men) should also take it to heart with regard to their briefcases, as should high school and college students of both sexes in relation to their backpacks and book bags."
From Snopes.com