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Volume 20, Number 4—April 2014

Research

Large Outbreak of Cryptosporidium hominis Infection Transmitted through the Public Water Supply, Sweden

Micael WiderströmComments to Author , Caroline Schönning, Mikael Lilja, Marianne Lebbad, Thomas Ljung, Görel Allestam, Martin Ferm, Britta Björkholm, Anette Hansen, Jari Hiltula, Jonas Långmark, Margareta Löfdahl, Maria Omberg, Christina Reuterwall, Eva Samuelsson, Katarina Widgren, Anders Wallensten, and Johan Lindh
Author affiliations: Umeå University, Umeå, Sweden (M. Widerström, M. Lilja, M. Ferm C. Reuterwall, E. Samuelsson); Jämtland County Council, Östersund, Sweden (M. Widerström, M. Omberg); Public Health Agency of Sweden, Soina, Sweden (C. Schönning, M. Lebbad, G. Allestam, B. Björkholm, A. Hansen, J. Långmark, M. Löfdahl, K. Widgren, A. Wallensten, J. Lindh); Mid Sweden University, Östersund, (T. Ljung,); Östersund Municipality, Östersund (J. Hitula); and Karolinska Institutet, Stockholm (J. Lindh)

Main Article

Table 5

Presence of Cryptosporidium oocysts in environmental samples collected in Östersund, Sweden, November 27, 2010– March 22, 2011*

Sample type No. samples No. positive samples Analyzed volume, L Presumptive no. oocysts, min–max/10 L Confirmed no. oocysts, min–max/10 L Time span for positive samples
Raw water† 18 10 100 0.2–3.1 0.1–0.7 2010 Nov 27–2011 Feb 9
Drinking water, WTP-Ö† 7 7 800–1,500 0.047–1.4 0.02–1.3 2010 Nov 27–2011 Jan 20
Drinking water, distribution network 9 9 800–1,400 0.063–0.36 0.05–0.05 2010 Nov 29–2011 Jan 31
Wastewater, untreated† 21 13 0.05‡ 200–270,000 §–160,000 2010 Nov 29–2011 Feb 17
Wastewater, treated 15 14 0.25–0.3‡ 30–21,000 30–10,000 2010 Dec 1–2011 Jan 24
Recipient (Lake Storsjön) 14 8 9–10 2–21 1–18 2010 Nov 29–2011 Mar 22
Connected streams 8 5 2–10 1,300–5,000 950–3,500 2010 Nov 30–Dec 14
Other¶ 10 2 10–17 1–3 1–3 2010 Nov 30–2011 Jan 17
Total 102 68 0.047–270,000 0.02–160,000 2010 Nov 27–2011 Mar 22

*Min, minimum; max, maximum; WTP-Ö, water treatment plant–Östersund.
†Details are available in Technical Appendix Figures 1 and 2.
‡These samples consisted of 30-mL aliquots from every 50–60 m3 of wastewater produced over 24 h.
§Not possible to determine the lowest density by microscopy because of substantial background material in the concentrated water sample.
¶Samples from sources, such as swimming pools, water used to flush the distribution network, and sediment from fire hydrants.

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