Text: 1) It is often the case that most people exposed to an infectious agent don't develop the disease. Among a group of people exposed to a disease agent, the proportion of people who develop the disease is the "attack rate."

For example, among persons infected with cholera

- 75% will have no symptoms

- 20% will have mild or moderate diarrhea

- < 5% will have severe clinical cholera infection

Among those who develop severe cholera infection, as many as 95% will die if they are not treated. This is referred to as the "case-fatality rate."

2) In this outbreak the 14 cases seen in people who denied kiddy pool exposure were probably secondary cases. For example, a mother who swam in the kiddy pool with her toddler might have then passed out snacks or sandwiches to other members of the family without washing her hands, and Giardia eggs may have been ingested by other family members as a result.