Ahead of Print -Large Outbreak of Cryptosporidium hominis Infection Transmitted through the Public Water Supply, Sweden - Volume 20, Number 4—April 2014 - Emerging Infectious Disease journal - CDC

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Ahead of Print -Large Outbreak of Cryptosporidium hominis Infection Transmitted through the Public Water Supply, Sweden - Volume 20, Number 4—April 2014 - Emerging Infectious Disease journal - CDC

Volume 20, Number 4—April 2014

Research

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

Article Contents

• Methods
• Results
• Discussion
• Acknowledgments
• References
• Figure 1
• Figure 2
• Figure 3
• Table 1
• Table 2
• Table 3
• Table 4
• Table 5
• Technical Appendix - 312 KB 
• Suggested Citation

Micael Widerström, 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, Stockholm, 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)

Suggested citation for this article

Abstract

In November 2010, ≈27,000 (≈45%) inhabitants of Östersund, Sweden, were affected by a waterborne outbreak of cryptosporidiosis. The outbreak was characterized by a rapid onset and high attack rate, especially among young and middle-aged persons. Young age, number of infected family members, amount of water consumed daily, and gluten intolerance were identified as risk factors for acquiring cryptosporidiosis. Also, chronic intestinal disease and young age were significantly associated with prolonged diarrhea. Identification of Cryptosporidium hominis subtype IbA10G2 in human and environmental samples and consistently low numbers of oocysts in drinking water confirmed insufficient reduction of parasites by the municipal water treatment plant. The current outbreak shows that use of inadequate microbial barriers at water treatment plants can have serious consequences for public health.

Protozoan parasites of the genus Cryptosporidium can cause gastrointestinal illness in humans and animals (1). Twenty-six species and >60 genotypes have been identified (2). C. parvum andC. hominis are the most prevalent species that infect humans (1,3). Cryptosporidiosis is transmitted mainly by the fecal–oral route, usually through oocyst-contaminated water or food or by direct contact with an infected person or animal (2). Infectivity is dose dependent and certain subtypes are apparently more virulent, requiring only a few oocysts to establish infection (1,4). In healthy persons, gastrointestinal symptoms usually resolve spontaneously within 1–2 weeks, although asymptomatic carriage can occur (2). Nonetheless, in immunocompromised patients, severe life-threatening watery diarrhea can develop (2). Information is limited regarding the long-term effects of Cryptosporidium infection (3,5,6).

The global incidence of cryptosporidiosis is largely unknown, although the disease was recently identified as one of the major causes of moderate to severe diarrhea in children <5 years of age in low-income countries (7). In Sweden, cryptosporidiosis has been a notifiable disease since 2004, and ≈150 cases (≈1.7/100,000 population/year) were reported annually until 2009. However, cryptosporidiosis is probably underreported, mainly because sampling from patients with gastrointestinal symptoms and requests for diagnostic tests are insufficient (3,8).

Because of some inherent characteristics of the pathogen, Cryptosporidium infection has critical public health implications for drinking water and recreational waters. The oocysts are excreted in large numbers in feces, can survive for months in the environment (5), and are resistant to the concentrations of chlorine commonly used to treat drinking water (9). The first reported outbreak of waterborne human cryptosporidiosis occurred in the United States in 1984 (10), and since then, numerous outbreaks involving up to hundreds of persons have been identified in several parts of the world (11,12). However, only a few very large outbreaks have been documented (13–15); the most extensive occurred in 1993 in Milwaukee, Wisconsin, USA, in which ≈400,000 persons were infected with Cryptosporidium oocysts by drinking water from a water treatment plant (WTP) (14). Cryptosporidium spp. are the predominant protozoan parasites causing waterborne outbreaks worldwide (11). In 2012, an increase inCryptosporidium infections, particularly by C. hominis IbA10G2, was reported in Europe (16).

In Sweden, only 1 drinking water outbreak involving Cryptosporidium has been recognized (Y. Andersson, pers. comm.), and a C. parvum outbreak associated with fecal contamination of a public swimming pool occurred in 2002 and affected ≈1,000 persons (17). A study ofCryptosporidium species and subtypes isolated from samples from 194 patients in Sweden during 2006–2008 identified 111 C. parvum infections and 65 C. hominis infections. Most patients with C. hominis infection had been infected abroad, and only 3 were considered to have sporadic domestic infections (3). A recent investigation of Cryptosporidium in raw water from 7 large WTPs in Sweden (not including the WTP of interest in the present study) identified 23 (11.5%) of 200 positive samples containing 1–30 oocysts/10 L, although neither species nor subtypes were analyzed (18).

Figure 1

Figure 1. . Map of Lake Storsjön, showing water currents (arrows) and locations of wastewater treatment plant, water treatment plant, and contaminating stream after Cryptosporidiuminfection outbreak, Östersund, Sweden, 2010–2011.

The city of Östersund is located in central Sweden and has a population of ≈60,000. The major WTP in Östersund (WTP-Ö) draws surface water from nearby Lake Storsjön and supplies drinking water to ≈51,000 of the city’s inhabitants. At the time of the onset of the outbreak reported here, the purification process at WTP-Ö included pre-ozonation, flocculation, and sedimentation, followed by rapid sand filtering and chloramination. WTP-Ö is situated 4 km upstream from the major wastewater treatment plant (WWTP-Ö) to ensure that the drinking water intake will not be affected by the wastewater outlet (Figure 1).

In late November 2010, the County Medical Office in Östersund received reports from several employers that 10%–20% of employees had gastroenteritis. The office advised that patients with acute gastroenteritis be tested for bacterial, viral, and protozoan pathogens. Among 20 patients from whom samples were obtained, 14 cases of cryptosporidiosis were detected on November 26. The local health advice line received numerous calls from persons with gastroenteritis, most of whom lived within the municipality (19). These facts indicated that the outbreak could be traced to the drinking water, and thus a boil-water advisory was issued for the municipality on November 26. This study describes the outbreak investigation and outlines the extent of the outbreak, clinical characteristics of persons infected, and risk factors for acquiring cryptosporidiosis.

Acknowledgments

We thank Joyce Eriksson, Tomas Nilsson, Jessica Nääs, and Lill Welinder for their excellent technical assistance. We also thank Johan Wiström for invaluable intellectual comments.

This work was supported by grants from the Research and Development Unit, Jämtland County Council, Sweden, and the Medical Faculty of Umeå University, Umeå, Sweden.

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Figures

• Figure 1. . Map of Lake Storsjön, showing water currents (arrows) and locations of wastewater treatment plant, water treatment plant, and contaminating stream after Cryptosporidiuminfection outbreak, Östersund, Sweden, 2010–2011.
• Figure 2. . Epidemiologic curve of data from the electronic survey (10,653 participants; blue) and written questionnaire (434 participants; red) showing number of patients with suspected cases by date of onset...
• Figure 3. . Percentage of ill persons and mean duration of symptoms fulfilling the case definition, stratified by age group during Cryptosporidium infection outbreak, Östersund, Sweden, 2010–2011. Error bars represent ±1...

Tables

• Table 1. Distribution of survey respondents and attack rate in Cryptosporidium infection outbreak, Östersund, Sweden, 2010–2011
• Table 2. Distribution of respondents and relapse of diarrhea among surveyed case-patients in the Cryptosporidium infection outbreak, Östersund, Sweden, 2010
• Table 3. Clinical characteristics of surveyed case-patients and non–case-patients in theCryptosporidium infection outbreak, Östersund, Sweden, 2010-2011
• Table 4. Risk factors for cryptosporidiosis and duration of infection in the Cryptosporidiuminfeaction outbreak, Östersund, Sweden, 2010 –2011
• Table 5. Presence of Cryptosporidium oocysts in environmental samples collected in Östersund, Sweden, November 27, 2010– March 22, 2011

Technical Appendix

• Technical Appendix. . Methods used in molecular analysis of CryptosporidiumFigure 1. Number of CryptosporidiumFigure 2.. Number of CryptosporidiumCryptosporidium oocysts in environmental samples collected in municipalities near Lake...  312 KB 

Suggested citation for this article: Widerström M, Schönning C, Lilja M, Lebbad M, Ljung T, Allestam G, et al. Large outbreak of Cryptosporidium hominis infection transmitted through the public water supply, Sweden. Emerg Infect Dis [Internet]. 2014 Apr [date cited].http://dx.doi.org/10.3201/eid2004.121415

DOI: 10.3201/eid2004.121415