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Volume 11, Number 2—February 2005

Research

Sporadic Cryptosporidiosis Decline after Membrane Filtration of Public Water Supplies, England, 1996–2002

Stella Goh*, Mark Reacher†Comments to Author , David P. Casemore‡, Neville Q. Verlander§, André Charlett§, Rachel M. Chalmers¶, Margaret Knowles#, Anthony Pennington*, Joy Williams*, Keith Osborn**, and Sarah Richards††
Author affiliations: *Carlisle and District Primary Care Trust, Carlisle, United Kingdom; †Health Protection Agency, Cambridge, United Kingdom; ‡University of Wales, Aberystwyth, Ceredigion, Wales, United Kingdom; §Health Protection Agency Centre for Infections, Colindale, London, United Kingdom; ¶Singleton Hospital, Swansea, Wales, United Kingdom; #Cumberland Infirmary, Carlisle, United Kingdom; **United Utilities, Great Sankey, Warrington, United Kingdom; ††West Cumberland Hospital, Whitehaven, United Kingdom

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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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