Original Article

Shigellosis Among Swimmers in a Freshwater Lake

Authors: Martha Iwamoto, MD, MPH, Gary Hlady, MD, MS, Monica Jeter, BA, Cindy Burnett, MPH, Cherie Drenzek, DVM, MS, Susan Lance, DVM, PHD, James Benson, BS, David Page, MD, MPH, Paul Blake, MD, MPH

Abstract

Objective: Shigella infection is highly communicable; however, outbreaks associated with swimming in recreational fresh water are rarely identified.


Materials and Methods: A cohort study of lake visitors was performed.


Results: Seventeen (24.6%) case patients among 69 persons who visited the lake over the holiday weekend were identified. Attack rates increased with increasing exposure to lake water; the risk of illness was greatest among swimmers who reported getting lake water in their mouths (relative risk = 5.37, 95% confidence interval = 2.2, 13.3). Shigella sonnei was isolated from stool samples of four of eight swimmers tested.


Conclusions: The outbreak likely was caused by fecal contamination of lake water by an infected swimmer; there was no evidence of sewage contamination into the lake. Fresh water is a potential source of infection in patients with acute gastroenteritis and recent exposure. Since testing and chlorination of lake water is impractical, prevention relies on avoidance of fecal contamination and/or minimizing ingestion of the water.


Key Points


* Lake water was the vehicle of transmission for Shigella sonnei.


* The most likely source of Shigella in the lake water was transient fecal contamination by an infected swimmer.


* Since there are no reliable methods for determining if fresh water is contaminated, prevention relies on avoidance of contamination and minimizing ingestion of lake water.

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References

1. DuPont HI, Levin MM, Homick RB, Formal SB. Inoculum size in shigellosis and implications for expected mode of transmission. J Infect Dis 1989;159:1126–1128.
 
2. Moore AC, Herwaldt BL, Craun GF, Calderon RL, Highsmith AK, Juranek DD. Surveillance for waterborne disease outbreaks: United States, 1991–1992. In: CDC Surveillance Summaries, November 19, 1993. MMWR Morb Mortal Wkly Rep 1993;42(SS-5):1–21.
 
3. Kramer MH, Herwaldt BL, Craun GF, Calderon RL, Juranek DD. Surveillance for waterborne disease outbreaks: United States, 1993–1994. In: CDC Surveillance Summaries, April 12, 1996. MMWR Morb Mortal Wkly Rep 1996;45(SS-1):1–33.
 
4. Levy DA, Bens MS, Craun GF, Calderon RL, Herwaldt BL. Surveillance for waterborne disease outbreaks: United States, 1995–1996. In: CDC Surveillance Summaries, December 11, 1998. MMWR Morb Mortal Wkly Rep 1998;47(SS-5):1–34.
 
5. Barwick RS, Levy DA, Craun GF, Beach MJ, Calderon RL. Surveillance for waterborne disease outbreaks: United States, 1997–1998. In: CDC Surveillance Summaries, May 26, 2000. MMWR Morb Mortal Wkly Rep 2000;49(SS-5):1–35.
 
6. Lee SH, Levy DA, Craun GF, Beach MJ, Calderon RL. Surveillance for waterborne disease outbreaks: United,1999–2000. In: CDC Surveillance Summaries, November 22, 2002. MMWR Morb Mortal Wkly Rep 2002;51(SS-8):1–47.
 
7. Rosenberg MS, Hazlet KK, Schaefer J, Wells JG, Pruneda RC. Shigellosis from swimming. JAMA1976;236:1849–1852.
 
8. Keene WE, McAnulty JM, Hoesly FC, et al. A swimming-associated outbreak of hemorrhagic colitis caused by Escherichia coli O157:H7 and Shigella sonnei. N Engl J Med 1994;331:579–584.
 
9. Makintubee S, Mallonee J, Istre GR. Shigellosis outbreak associated with swimming. Am J Public Health 1987;77:166–168.
 
10. Sorvillo FJ, Waterman SH, Vogt JK, et al. Shigellosis associated with recreational water contact in Los Angeles County. Am J Trop Med Hyg 1988;38:613–617.
 
11. Environmental Protection Agency. Bacterial water quality standards for recreational waters (freshwater and marine waters): status report. Washington, DC: Environmental Protection Agency, June 2003. (Accessed March 22, 2005, at http://www.epa.gov/waterscience/beaches/local/statrept.pdf).
 
12. Calderon RL, Wood EW, DuFour AP. Health effects of swimmers and nonpoint sources of contaminated water. Int J Environ Health Res 1991;1:21–31.
 
13. Mitscherlich E, Marth EH. Microbial survival in the environment: bacteria and rickettsiae important in human and animal health. Berlin, Germany: Springer-Verlab, 1984:693-704.