Volume 11, Number 2—February 2005
Research
Sporadic Cryptosporidiosis Decline after Membrane Filtration of Public Water Supplies, England, 1996–2002
Stella Goh*, Mark Reacher†
, David P. Casemore‡, Neville Q. Verlander§, André Charlett§, Rachel M. Chalmers¶, Margaret Knowles#, Anthony Pennington*, Joy Williams*, Keith Osborn**, and Sarah Richards††
, David P. Casemore‡, Neville Q. Verlander§, André Charlett§, Rachel M. Chalmers¶, Margaret Knowles#, Anthony Pennington*, Joy Williams*, Keith Osborn**, and Sarah Richards††
Table 4
Incidence of sporadic cryptosporidiosis by water source, March 1, 1996–August 31, 2002
| Water source and time intervals* | Membrane filtration (MF) | Cases (n) | Person-years | Rate per 100,000 person-years | 95% CI† |
|---|---|---|---|---|---|
| Crummock Lake | |||||
| Before MF interval | No | 56 | 233,623 | 23.97 | (18.11, 31.13) |
| After MF interval | |||||
| Commissioning MF | Yes | 1 | 25,726 | 3.89 | (0.10, 21.66) |
| Established MF pre-FMDE | Yes | 1 | 33,970 | 2.94 | (0.07, 16.40) |
| Established MF and FMDE | Yes | 1 | 54,902 | 1.82 | (0.05, 10.15) |
| Established MF and post-FMDE | Yes | 3 | 31,490 | 9.53 | (1.96, 27.84) |
| Total after MF | Yes | 6 | 146,088 | 4.11 | (1.51, 8.91) |
| Ennerdale Lake | |||||
| Before MF interval | No | 43 | 191,053 | 22.51 | (16.29, 30.32) |
| After MF interval | |||||
| Commissioning MF | Yes | 0 | 20,258 | 0 | (0, 18.21) |
| Established MF pre-FMDE | Yes | 1 | 27,223 | 3.67 | (0.09, 20.47) |
| Established MF and FMDE | Yes | 2 | 46,387 | 4.31 | (0.52, 15.57) |
| Established MF and post-FMDE | Yes | 0 | 26,606 | 0 | (0, 13.86) |
| Total after MF | yes | 3 | 120,474 | 2.49 | (0.51, 7.28) |
| Other sources | |||||
| Before MF interval | No | 54 | 238,265 | 22.66 | (17.03, 29.57) |
| After MF interval | |||||
| Commissioning MF | No | 3 | 24,449 | 12.27 | (2.53, 35.86) |
| Established MF pre-FMDE | No | 4 | 32,257 | 12.4 | (3.38 , 31.75 ) |
| Established MF and FMDE | No | 3 | 51,997 | 5.77 | (1.19, 16.86) |
| Established MF and post-FMDE | No | 3 | 29,824 | 10.06 | (2.07, 29.40) |
| Total after MF | No | 13 | 138,527 | 9.38 | (5.00,16.05) |
*Time intervals. pre-MF (membrane filtration) March 1, 1996–February 29, 2000; post-MF March 1, 2000–August 31, 2002. Post-MF comprises the following: commissioning MF, March 1, 2000–July 31, 2000; established MF before foot and mouth disease epidemic (FMDE), August 1, 2000–February 20, 2001; established MF and FMDE, February 21, 2001–January 20, 2002; established MF and post-FMDE, January 21, 2002–August31, 2002.
†CI, confidence intervals.
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