DISCUSSION
Our results provide, to our knowledge, the largest summary of the gastroenteritis risk and related public health burden associated with recreational water exposure in the United States. Increased risk at the highest Enterococcus levels supports their use as a monitoring indicator for diarrhea risk among beachgoers, although the association between Enterococcus and illness was weaker at beaches without an identified source of human fecal pollution. The higher diarrhea risk among younger children associated with water exposure and larger illness burden attributable to swimming exposure were consistent with longer water contact times and a greater propensity to swallow water. An earlier analysis of this study’s freshwater cohorts reported higher swimming-associated gastrointestinal illness risk among children younger than 10 years compared with the overall population,8 but our findings provide evidence for heightened sensitivity among children across a broader set of beach conditions, including marine water and diffuse, “nonpoint” sources of pollution from urban runoff. Our analysis also highlights for the first time, to our knowledge, the largest attributable burden among the youngest children, those aged 0 to 4 years.