High Sensitivity of Children to Swimming-Associated Gastrointestinal Illness

Abstract

The authors respond: We disagree with Keith Linn's interpretation of our paper, “High Sensitivity of Children to Swimming-Associated Gastrointestinal Illness.”1 His comments are focused on hypothetical interpretation of our results as related to criteria development, rather than the science presented. Linn notes our definitions for gastrointestinal (GI) illness and swimming differ from those used previously.2,3 We clearly justify our rationale for both definitions, and we reject the implication that it is misleading to revisit these definitions, previously used in studies done over 20 years ago. We make no attempt, as Linn implies, to establish an “illness rate threshold” for comparison with current criteria. We explicitly do not make such comparisons because there are substantial differences between our study and previous studies.2,3 These differences include the follow-up period, statistical methodology, and definitions of illness, as well as the indicators and methods used. These differences make simplistic, direct comparisons among studies problematic, and Linn's attempts at such direct comparisons are not justified. The enhanced sensitivity among children is clearly presented. By highlighting a small range of data, Linn ignores the overall effect. As Linn points out, the difference between swimming and nonswimming children is less than that between all swimmers and nonswimmers in water of good microbial quality as measured by Enterococcus quantitative polymerase chain reaction cell equivalents (QPCR CE), reflecting baseline characteristics and differences between swimming and nonswimming children. This says nothing of the susceptibility of children to GI illness associated with swimming in water of poor microbial quality. With increasing exposure to Enterococcus QPCR CE, the risk of illness among swimmers who are children increases at a greater rate compared with other age groups. The odds of illness among children increased 69% with every log increase in Enterococcus QPCR CE exposure, whereas the odds of illness among those aged 11–54 years and those 55 years and older increased 13% and 21%, respectively (Table 51). We do not suggest that “the sensitivity of children warrants adjustment of recreational water quality criteria.” Our conclusion was limited to the study itself and was presented in the following discussion: “children up to age 10 years were especially susceptible to GI illness following swimming exposure … this is the first study to demonstrate this sensitivity as a function of microbial water quality.” Timothy J. Wade Elizabeth Sams US Environmental Protection Agency National Health and Environmental Effects Research Laboratory Chapel Hill, NC Kristen P. Brenner Richard Haugland Larry Wymer Alfred P. Dufour US Environmental Protection Agency National Exposure Research Laboratory Cincinnati, OH