Outbreaks of Acute Gastrointestinal Illness Associated with a Splash Pad in a Wildlife Park — Kansas, June 2021

Clinical Laboratory and Epidemiologic Investigation

In Kansas, shigellosis is reportable, and patients are interviewed using standard case investigation forms. The initial investigation identified eight patients with shigellosis who reported entering the splash pad on June 11 and who all experienced signs and symptoms 12–73 hours later. Two of the eight patients had stool cultures positive for Shigella flexneri type 1; whole genome sequencing found no base pair differences between the two isolates. The remaining six patients had stool specimens tested using multiplex polymerase chain reaction and were positive for the Shigella/enteroinvasive Escherichia coli target (ipaH gene). Two of these six patients also had specimens that tested positive for the Shiga toxin target (stx₁/stx₂ genes); however, neither stool culture yielded Shiga toxin–producing E. coli.

KDHE and the wildlife park, through press releases and Facebook posts, encouraged patrons who visited the park during the period from the seasonal opening day (May 28) through June 19 to voluntarily complete an online outbreak questionnaire during July 12–August 4. The questionnaire requested information on demographic characteristics, activities during wildlife park visits, and signs and symptoms of respondents who experienced gastrointestinal illness (case-patients). Participants who did not experience gastrointestinal illness were considered control respondents.

Summary statistics and bivariate analyses assessed potential exposures. Where item nonresponse was present, missing values were multiply imputed^§ (1,2). Unadjusted and adjusted odds ratios and CIs were estimated using Firth penalized maximum likelihood logistic regression (3), which can mitigate bias due to rare events. Multiply imputed analyses were compared with complete case analyses. All statistical analyses were conducted in R (version 4.1.3, R Foundation). This activity was reviewed by CDC and was conducted consistent with applicable federal law and CDC policy.^¶

Analysis of data from 404 respondents who only visited the park once during May 28–June 19 identified two distinct outbreaks (Figure 1). Among 72 respondents** who visited on June 11, 21 (29%) experienced illness meeting the shigellosis case definition (three or more loose stools in 24 hours with onset 12–73 hours after visiting the wildlife park on June 11). The median ages of shigellosis case-patients and controls^†† were 5 years (range = 1–15 years) and 11 years (range = 1–70 years), respectively (p<0.01).^§§ Both case-patients and controls were predominantly female (62% and 67%, respectively). Playing in the splash pad water was not associated with illness; however, getting splash pad water in the mouth was associated with illness (multivariate complete case adjusted odds ratio [aOR_C] = 10.2, p = 0.007; aOR_MI = 6.4, p = 0.036) (Table) (Figure 2). Touching or feeding lemurs (the only nonhuman primates available for patron interaction) was not associated with illness. Three case-patients were hospitalized for an average of 3 days; no deaths were reported.

Among 27 respondents^¶¶ who visited the wildlife park on June 18, six (22%) experienced illness meeting the norovirus infection case definition (vomiting or three or more loose stools in 24 hours with onset 12–56 hours after visiting the wildlife park on June 18). Responses for three case-patients indicated a health care provider diagnosed norovirus infection. The median ages of norovirus infection case-patients and controls*** were 5 years (range = 1–38 years) and 20 years (range = 3–63 years), respectively (p = 0.04). Case-patients and controls were predominantly female (83% and 68%, respectively). All six case-patients played in the splash pad water and got the splash pad water in their mouths (Figure 2). Getting splash pad water in the mouth was associated with illness (aOR_C = 24.1, p = 0.007; aOR_MI = 28.6, p = 0.006). One case-patient was hospitalized for 1 day; no deaths were reported.

Environmental Microbiology Laboratory and Environmental Health Investigation

The wildlife park’s unregulated splash pad included jets, tipping buckets, and slides. SCHD worked with the splash pad operator and CDC to identify potential factors contributing to the outbreaks. Water stood in the collection tank (into which water drains after spraying users and before it is filtered, disinfected, and resprayed) overnight instead of being continuously recirculated, filtered, and chlorinated. The splash pad did not have an automated controller to measure and help maintain the free chlorine concentration needed to prevent pathogen transmission. In addition, no staff member had documentation of having completed standardized operator training. Splash pad water samples were collected on June 19 from the four sand filters, seven pumps, and collection tank. CDC tested the samples for Shigella and fecal indicator bacteria.^††† Total coliforms were detected in three of the seven pumps feeding the splash pad features; E. coli was detected in one of the coliform-positive pumps.

Public Health Response

After the splash pad was closed, CDC drafted operation and management guidance for reopening, based on the 2018 MAHC (4). SCHD finalized the recommendations and shared them with the splash pad operator. On July 24, the operator reopened the splash pad to the public after voluntarily addressing gaps and implementing best practices, including continuously recirculating, filtering, and disinfecting water (MAHC 5.7.1.1.1 and 5.7.3.1);^§§§ using an automated controller (MAHC 5.7.3.7.1); and completing operator training (MAHC 6.1.2). After these interventions were implemented, no additional splash pad–associated illnesses were identified.

Discussion

Pathogens that cause gastrointestinal illness can be transmitted when water contaminated with feces from infected persons is ingested. Splash pads are intended for young children, aged <5 years. Young children are more likely to experience acute gastrointestinal illness including shigellosis and norovirus infection (5,6), and, because of inadequate toileting and hygiene skills, are more likely to contaminate the water. Swim diapers do not prevent contamination of water (7). Children also ingest more recreational water than do adults (8). One study of splash pad behaviors documented children wearing diapers, sitting on water jets, and placing their open mouths to the water (9). When splash pads jet or spray water, aerosolization depletes the free chlorine concentration, making it more difficult to maintain the minimum concentration necessary to prevent pathogen transmission. These two splash pad outbreaks were caused by pathogens readily inactivated by free chlorine,^¶¶¶ indicating that the outbreaks might have been prevented by maintaining water disinfection. The environmental health investigation findings elucidated why these outbreaks occurred; no additional cases were identified after the operator implemented reopening guidance, suggesting that pathogen transmission can be prevented.

Splash pads typically do not have standing water in the user area. Thus, they might not meet a jurisdiction’s definition of a treated recreational water venue (e.g., pool) open to the public, which can exempt them from regulation under public health codes. In 1997, the first reported splash pad–associated outbreak also occurred near animals**** (10). Although neither the investigation of the 1997 outbreak nor this shigellosis outbreak found evidence of waterborne zoonotic pathogen transmission, they highlight the potential for such transmission. In public animal settings with splash pads, using the splash pad before entering animal areas or changing shoes before entering the splash pad could prevent the introduction and transmission of zoonotic pathogens.

The findings in this report are subject to at least five limitations. First, daily overall wildlife park and splash pad patron counts were not available, and respondent representativeness was not assessed. Second, case-patient and control respondent counts were small, and analyzing data by wildlife park visit date further limited statistical power. However, for visit dates other than June 11 or 18, no case-patients had clinical laboratory evidence supporting detection of the same pathogen. Missing data were multiply imputed to partially address limited statistical power. Third, wording of one response choice lacked clarity^†††† and might have increased error in exposure observations resulting in increased SE and reduced significance in the association between the splash pad and illness. Fourth, small samples can cause rare events to be overrepresented, leading to bias. Statistical techniques, including Firth penalized logistic regression, were employed to account for this. Finally, the time elapsed from splash pad entry until study response could have led to recall bias.

By identifying factors contributing to outbreaks, environmental health specialists provide data central to developing effective mitigation and prevention strategies for outbreaks associated with treated recreational water venues open to the public. As splash pad use increases, exempting splash pads from regulation under public health codes needs to be reconsidered. CDC’s MAHC recommendations can be voluntarily adopted by U.S. jurisdictions. Environmental health specialists also enforce public health codes through inspections and serve as healthy and safe swimming resources for operators.^§§§§ To further promote healthy and safe swimming, environmental health specialists can partner with the aquatics sector to engage the public and increase awareness of the importance of healthy swimming steps. Efforts to prevent splash pad–associated outbreaks need to be targeted to caregivers, with prevention messages that include “Don’t get in the water if sick with diarrhea,” “Don’t stand or sit above the jets,” and “Don’t swallow the water.”