Part 2

Data from a hypothetical investigation of an epidemic of rubella in a city are given in the following table:

Table 2

Age group	Number in city	Number ill	Number not ill but with antibody rise	Number uninfected	Percent infected
0-9	20400	11000	7400	2000	90
10-19	12900	7000	4600	1300	90
20-39	16100	8800	5700	1600	90
40-59	7800	4200	2800	800	90
60+	4200	200	200	3800	10
Totals	61400	31200	20700	9500

1. What is the incidence of illness for all age groups (as a percentage)?
2. What is the percentage of infection that is asymptomatic?
3. Based on the age-specific infection rates, when did rubella previously occur in this city in relation to the current epidemic?