Promotion of Healthy Swimming After a Statewide Outbreak of Cryptosporidiosis Associated with Recreational Water Venues — Utah, 2008–2009

During the summer of 2007, Utah experienced a statewide outbreak of gastrointestinal illness caused by Cryptosporidium, a parasite transmitted via the fecal-oral route. Approximately 5,700 outbreak-related cases were identified across the state (1). Of 1,506 interviewed patients with laboratory-confirmed cryptosporidiosis, 1,209 (80%) reported swimming in at least one of approximately 450 recreational water venues during their potential 14-day incubation period (2). Cryptosporidium is extremely chlorine-tolerant, and secondary or supplemental disinfection with ultraviolet light or ozone can control but not prevent outbreaks. Because swimmers are the primary source of Cryptosporidium contamination, healthy swimming campaigns are needed to increase awareness and practice of healthy swimming behaviors, especially not swimming while ill with diarrhea (i.e., swimming while ill with diarrhea can lead to gross contamination of recreational water). Before the 2008 summer swimming season, Utah public health agencies launched a multimedia healthy swimming campaign. To assess knowledge of healthy swimming, a survey of Utah residents was conducted during July–September 2008. The results of that survey found that 96.1% of respondents correctly indicated that "it is not OK to swim if you have diarrhea." In a separate national survey in 2009, 100% of Utah residents but only 78.4% of residents of other states correctly indicated that "not swimming while ill with diarrhea protects others from recreational water illnesses (RWIs)." No recreational water–associated outbreaks were detected in Utah during 2008–2011. The healthy swimming campaign, as part of a multipronged prevention effort, might have helped prevent recreational water–associated outbreaks of cryptosporidiosis in Utah.

Before the 2008 summer swimming season, Utah's state and local public health agencies teamed with community partners to control recreational water–associated transmission of Cryptosporidium (3). For example, the Salt Lake Valley Health Department (SLVHD) collaborated with pool operators to establish fecal incident–response protocols and install secondary or supplement disinfection systems to inactivate Cryptosporidium at 75 treated recreational water venues. SLVHD also collaborated with the Utah Department of Health and diagnostic laboratories to expedite reporting of cryptosporidiosis cases to public health authorities. To engage the public in prevention, SLVHD led efforts to disseminate healthy swimming messages via a website, two television advertisements, public service radio announcements, and posters at pools (e.g., "A Swimming Pool is Like a Community Bathtub"). In addition, targeted messages were disseminated to schools, competitive water sports teams, and licensed child care facilities. SLVHD also conducted a press conference during Recreational Water Illness and Injury Prevention Week, which is held each year the week before the Memorial Day holiday.*

To assess awareness of the previous year's outbreak and the education campaign and knowledge of healthy swimming, the Utah Department of Health surveyed residents of four counties (Davis, Salt Lake, Utah, and Weber) during July–September 2008 using a Utah Behavioral Risk Factor Surveillance System (BRFSS) callback survey (4). The four counties represented 75% of the Utah population† and were the counties of residence for 86% of patients with laboratory-confirmed cryptosporidiosis in 2007. Eligible adults had participated in Utah's BRFSS survey previously and indicated a willingness to participate in future surveys. Of the 642 adults§ whom UDOH attempted to recontact, 499 (78%) completed interviews. Knowledge of RWIs¶ and healthy swimming also was assessed nationally during August–September 2009 using HealthStyles, a national postal survey that assesses adults' health-related knowledge, attitudes, and behaviors (5). HealthStyles surveys were mailed to a nationally representative sample of 7,004 households; an adult from 4,556 (65%) households returned the survey. Statistical software was used to apply sampling weights and account for the complex sample design of both survey. Statistical significance (p≤0.05) was determined using Rao-Scott adjusted chi-squares.

In the BRFSS callback survey, 91.3% of respondents reported being aware of the 2007 outbreak (Table 1). A greater percentage of women (36.2%) than men (16.7%) recalled seeing healthy swimming campaign posters at pools. Greater percentages of adults with children in their households compared with those with no children in their households sought information about the outbreak (24.6% versus 9.5%) and saw posters at pools (35.3% versus 16.1%). Conversely, a greater percentage of those without children recalled seeing television advertisements (51.4%) compared with those with children (34.1%). Among all respondents, 96.1% correctly indicated that "it is not OK to swim if you have diarrhea," and 70.4% correctly indicated that "chlorine does not kill germs instantly" (Table 2). A greater percentage of those who reported seeing any television advertisements correctly indicated that "it is not OK to swim if you have diarrhea" (98.6% versus 94.2%) and that "pool water quality is not the same as drinking water quality" (90.9% versus 74.9%) than those reporting not seeing any posters at pools or television advertisements. All of the above differences were significant.

In the 2009 HealthStyles survey, 100% of Utah residents but only 78.4% of residents of other states correctly indicated that "not swimming when you have diarrhea" protects others from RWIs (Table 3). A greater percentage of Utah residents than residents of other states correctly responded to five of eight healthy swimming questions, and most differences were significant (Table 3). For example, 96.4% of Utah residents compared with 85.7% of residents of other states correctly identified "not swallowing water you swim in" as a healthy swimming behavior, and 85.8% of Utah residents compared with 65.9% of residents of other states correctly indicated that "chlorine does not kill germs instantly." However, a smaller percentage of Utah residents than residents of other states identified "making sure that pools are treated" as a healthy swimming behavior (49.3% versus 86.0%).

Reported by

Gary Edwards, MS, Linda Bogdanow, Salt Lake Valley Health Dept; Robert T. Rolfs, MD, Jennifer Wrathall, MPH, Utah Dept of Health. Sarah A. Collier, MPH, Michele C. Hlavsa, MPH, Michael J. Beach, PhD, Christine E. Prue, PhD, Catherine O. Hough, MPH, Alexandra L. Shevach, MPH, Div of Foodborne, Waterborne, and Environmental Diseases, National Center for Emerging and Zoonotic Infectious Diseases; Renee M. Calanan, PhD, EIS Officer, CDC. Corresponding contributor: Michele C. Hlavsa, mhlavsa@cdc.gov, 404-639-1700.

Editorial Note

This report is the first published assessment of healthy swimming knowledge either nationally or after a recreational water–associated outbreak. Greater percentages of Utah residents than residents of other states identified "not swimming when you have diarrhea" and "not swallowing water you swim in" as healthy swimming behaviors. These differences might reflect significant differences in knowledge between Utah residents and residents of other states with regard to recognizing that chlorine does not kill pathogens instantly.

Chlorine is the primary barrier to pathogen transmission in treated recreational water venues. Historically, establishment and enforcement of water quality standards by public health authorities and maintenance of water quality by the aquatics sector has been sufficient to prevent RWI outbreaks. However, the emergence of Cryptosporidium, a chlorine-tolerant pathogen, has meant that chlorination alone is no longer sufficient to protect swimmer health. Cryptosporidium can survive in water at CDC-recommended free chlorine levels of 1–3 mg/L** for 3.5–10.6 days (6). Since the first reported U.S. swimming pool–associated outbreak of cryptosporidiosis in 1988, Cryptosporidium has been responsible for the significant (negative binomial regression, p<0.001) increase in the incidence of recreational water–associated outbreaks (CDC, unpublished data, 2012). During 2007–2008, a total of 59 (72%) of 82†† treated recreational water–associated outbreaks with an identified infectious etiology were caused by Cryptosporidium (1).

To prevent recreational water–associated outbreaks of cryptosporidiosis, education of swimmers is needed. A single diarrheal contamination incident can introduce 107–108 Cryptosporidium oocysts to a typical treated recreational water venue, enough that a single mouthful could lead to infection (7,8). Moreover, a single infected swimmer potentially can contaminate multiple recreational water venues, causing a communitywide outbreak (1,2). Engineering (e.g., secondary or supplemental disinfection systems) and enforcement (e.g., the Model Aquatic Health Code,§§ which addresses the public health threat presented by Cryptosporidium) can minimize contamination and help control recreational water–associated outbreaks of cryptosporidiosis. However, the highly infectious, chlorine-tolerant attributes of Cryptosporidium mean that effective prevention relies on swimmers practicing healthy swimming behaviors.

The findings in this report are subject to at least five limitations. First, the cross-sectional design of the ecologic studies does not permit any conclusions about the cause and effect relationship between the education campaign and respondent knowledge. Moreover, no baseline measurements of healthy swimming knowledge of Utah residents were taken before the outbreak or education campaign, so no direct evidence of an increase in healthy swimming knowledge in Utah exists. Second, assessment of healthy swimming knowledge might be susceptible to social desirability bias (e.g., respondents might answer a question about swimming while ill with diarrhea in a manner that will be viewed favorably by others). Third, the BRFSS and HealthStyles surveys assessed knowledge, not behavior. Whether increased healthy swimming knowledge translates to increased likelihood of healthy swimming behavior is unknown. However, no recreational water–associated outbreaks were detected in Utah during 2008–2011. Fourth, the nationally representative HealthStyles survey sample was drawn from a nonrandom sample, and the response rate was only 65%. Finally, respondents in the Utah BRFSS callback survey were from a pre-identified group of residents who had indicated a willingness to participate in future surveys and who might not be representative of the general population of Utah.

To reverse the increasing incidence of recreational water–associated outbreaks of cryptosporidiosis, healthy swimming campaigns must reach those persons (21.6% in the national HealthStyles survey) who do not know that swimming while ill with diarrhea is an unhealthy swimming behavior. Although the cost of airtime for television and radio advertising might appear prohibitive for many state and local public health agencies, such expenditures should be weighed against the cost (e.g., public health staff time and health-care expenditures) of communitywide cryptosporidiosis outbreaks (3,9). Health promotion efforts such as holding a press conference during Recreational Water Illness and Injury Prevention Week or developing Internet content are less costly opportunities to disseminate healthy swimming messages. Developing seasonally recurring health promotion activities that 1) increase the public's perception of their vulnerability to and the severity of RWIs, 2) emphasize the effectiveness of healthy swimming behaviors,¶¶ and 3) increase swimmers' confidence in their ability to effectively implement these simple prevention steps might increase healthy swimming behaviors (10) and prevent future diarrheal contamination of recreational water and associated outbreaks of cryptosporidiosis.

References

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