Risk estimates of occurrence of a cluster within four weeks for any cluster, a confirmed cluster, and a serogroup B and C cluster by setting, in England and Wales from April 1995 to March 2001
| Setting | 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. | |||||
| *The observed number of confirmed, B, and C clusters reported here differ from those in table 2 as only clusters in which subsequent cases are the same serogroup or classification (confirmed) as the initial case have been included. | |||||
| Preschool | Any | 20 | 0.725 | 27.6 (15.2 to 39.9) | 69.9 (38.7 to 101.2) |
| Confirmed | 11 | 0.327 | 33.6 (16.8 to 60.0) | 57.3 (28.7 to 102.1) | |
| B | 6 | 0.135 | 44.5 (16.3 to 96.3) | 48.6 (17.8 to 105.4) | |
| C | 4 | 0.042 | 95.2 (26.2 to 42.6) | 61.6 (16.9 to157.1) | |
| Primary | Any | 43 | 7.910 | 5.4 (3.8 to 7.1) | 5.7 (4.0 to 7.4) |
| Confirmed | 22 | 2.495 | 8.8 (5.1 to 12.6) | 5.2 (3.0 to 7.4) | |
| B | 12 | 0.739 | 16.2 (8.4 to 28.1) | 5.2 (2.7 to 9.0) | |
| C | 6 | 0.511 | 11.7 (4.3 to 25.4) | 3.3 (1.2 to 7.2) | |
| Secondary | Any | 46 | 12.849 | 3.6 (2.5 to 4.6) | 3.0 (2.1 to 3.9) |
| Confirmed | 31 | 5.209 | 5.9 (3.8 to 8.1) | 3.2 (2.0 to 4.3) | |
| B | 7 | 1.032 | 6.8 (2.7 to 14.0) | 1.6 (0.6 to 3.3) | |
| C | 16 | 1.671 | 9.6 (5.4 to 14.7) | 3.1 (1.7 to 4.7) | |
| Independent | Any | 5 | 0.965 | 5.2 (1.7 to 12.0) | 5.4 (1.7 to 12.5) |
| Confirmed | 2 | 0.338 | 5.9 (0.7 to 21.3) | 3.6 (0.4 to 13.1) | |
| B | 0 | 0.089 | 0 (0.0 to 41.7) | 0 (0.0 to 13.1) | |
| C | 1 | 0.082 | 12.2 (0.3 to 67.9) | 3.9 (0.1 to 21.7) | |