How may I calculate the confidence interval of the mean of several incidences each have a confidence interval?
Example: Incidence of DVT in patients with lower limb erysipelas
Patients DVT DVT%
43 3 6.9 (1.5–19.1)
40 6 15 (5.7–29.8)
10 0 0 (0.0–30.9)
155 4 2.6 (0.7–6.5)
30 3 10 (2.1–26.5)
Figures in parentheses are 95% confidence intervals. Ponderated incidence with 95% confidence interval:
5.8% (3.3–9.2).

How they have calculated the Confidence Interval: 3.3 - 9.2?