Risk estimates for occurrence of a cluster between 2 and 28 days for any cluster, a confirmed cluster, and a serogroup B and C cluster in a preschool setting, in England and Wales from April 1995 to March 2001
| Type of cluster | Observed number of clusters | Expected number of clusters | RR (95% CI) | AR per 100 000 (95% CI) |
|---|---|---|---|---|
| RR, Relative risk; AR, absolute risk. | ||||
| Any | 14 | 0.670 | 20.8 (11.6 to 34.2) | 49.0 (27.3 to 80.4) |
| Confirmed | 8 | 0.300 | 26.4 (11.4 to 52.1) | 41.7 (18.0 to 82.3) |
| B | 4 | 0.130 | 31.9 (8.8 to 81.4) | 32.4 (8.9 to 82.7) |
| C | 3 | 0.039 | 76.9 (15.9 to 225.4) | 46.2 (9.6 to 135.6) |