# Relationship of Tijuana River Flow and Ocean Bacteria Counts and Emergency Department Diarrhea Cases

## TL;DR

This study found that increased flow in the Tijuana River, especially after a hurricane, correlates with higher rates of diarrhea cases at a nearby emergency department.

## Contribution

The study provides new evidence linking transboundary river flow and ocean bacterial contamination to emergency department visits for diarrhea.

## Key findings

- After Hurricane Hillary, the Tijuana River flow rate increased significantly, leading to a 3.25-fold rise in ED diarrhea cases.
- A significant correlation was found between Tijuana River flow rates and ED diarrhea case levels during the 2023 dry season.
- Fecal bacterial counts on the southern San Diego coastline were linked to increased diarrhea cases in the study period.

## Abstract

The Tijuana River, which affects southern San Diego Beaches, is severely contaminated with untreated sewage. Exposure to pathogens can lead to various health problems, commonly gastrointestinal (GI) illnesses. We aimed to look for any relationship between Tijuana River flow rates and ocean pollution levels and levels of diarrhea at a nearby Emergency Department (ED).

In this retrospective study that spanned the 2023 dry season and included Hurricane Hillary, we compared Tijuana River flow rates and fecal bacterial counts on the southern San Diego County coastline to the number of visits to a nearby ED, specifically a 225-patient sample size, with the chief complaint of diarrhea, a potential waterborne illness.

In late August of 2023, after Hurricane Hillary made landfall as a tropical storm in Baja California, Mexico, there was a large increase in the Tijuana River flow rate and a correspondingly significant increase in diarrhea cases at 3.25 times the mean, from a mean of 4.25 cases per week to 14 cases the week of Hurricane Hillary.

We found a significant correlation between Tijuana River transboundary flow rates and Emergency Department case levels of diarrhea, a known waterborne illness, in the summer of 2023.