Review basics on foodborne outbreak investigations and calculations in an appropriate epidemiology textbook.
No specific text required. For example: A few pages in Epidemiology by Leon Gordis or Procedures to Investigate Foodborne Illness includes this information.
3rd ed.
eBook copy available (http://vufind.carli.illinois.edu/vf-uiu/Record/uiu_7368993)
Newer edition available (http://vufind.carli.illinois.edu/vf-uiu/Record/uiu_7586449)