Early this month, San Diego County Public Health Services announced that experts had reviewed medical records in the South Bay and uncovered “no conclusive evidence” that cross-border pollution from Tijuana was causing increased sickness.
This finding was based on an “investigation” of records at South Bay Urgent Care Clinic, which had reported a surge in illnesses last August after summer storms caused a massive flow of sewage from the Tijuana River into the ocean.
Public Health officials indicated their review was performed to evaluate those claims. Yet it did not focus on the August incident. Instead, experts looked at medical records covering a two-week period in February, following a winter storm.
This seemed to defy common sense: Almost no one goes into the ocean during February, so a reasonable person would not expect to see a spike in illnesses during that period. Nevertheless, the findings led to a San Diego Union Tribune headline declaring, “County says it found no evidence of increased illness at South Bay Urgent Care tied to sewage spills.”
To better understand the county’s investigation, The Coronado News submitted written questions to County Public Health Services. Below are those questions, and the county’s responses, some of which have been edited for brevity.
Q: What was the purpose of your study?
The county: In response to concerns of increased gastrointestinal illnesses reported by a clinic in Imperial Beach, the public health department investigated these concerns through data collection and analysis of results in a two-week timeframe after a wet weather event. This was a survey conducted in response to community concerns about potential increases in gastrointestinal illnesses.
Q: Who asked you to perform the study, and why?
The county: County Public Health Services takes every report of illness seriously. We undertook this work in response to concerns from the Imperial Beach community.
Q: Was the research goal to learn whether illnesses increased as a result of airborne transmission, water transmission, or both?
The county: This was not a research project. The focus on gastrointestinal illnesses was due to the concern brought forth from a clinic that they were seeing increased gastrointestinal illness.
Q: If the goal was to learn whether illnesses increased as a result of water transmission, isn’t it grossly misleading and unscientific? How would a study in February — the dead of winter — provide such evidence at a time when virtually no one is using the ocean?
The county: The time periods that public health doctors and epidemiologists focused on involved periods of heavy rain. The community raised concerns that during periods of heavy rains and flooding, there was an increase of cases of gastrointestinal diseases. The public health department had also increased their surveillance since tropical storm Hilary and continues with increased surveillance.
Q: When you put out news that your investigation showed “no conclusive evidence of increased illness,” as the Union Tribune reported, were you attempting to create a perception that sewage-contaminated ocean water does not cause sickness and is not a public health threat?
The county: Exposure to sewage-contaminated water has always been, and remains, a threat to public health and safety. The county conducts daily testing of the beach water and posts signage so people know the condition of the local water. People who swim in or have contact with sewage or chemical polluted water face an expanded threat of illness.
Q: Did you also analyze the South Bay Urgent Care’s medical charts from August 2023 — the time period when doctors there reported a spike in illnesses — to see if caseloads correlated with increased sewage pathogens in the ocean water?
- If yes, what was the finding and why didn’t you also report that publicly?
- If no, why didn’t you study the August time period?
The county: We carefully reviewed the August 2023 clinic data with the Urgent Care’s medical staff. The number of actual people ill was far less than a graph they had shared because it was counting symptom/diagnosis codes, not people. An individual patient can have several symptoms/diagnosis codes during an illness.
For example if an individual comes in to the clinic with nausea, vomiting, and stomach pain that person was counted three times instead of one person. Also, the illness onsets were occurring too close to the rain event to be caused by it. Usually, it takes a day or two after exposure for a stomach illness and the resulting symptoms such as diarrhea to appear. Some of the cases shown were on the same day the rain was beginning.
Q: If your study was only intended to determine whether sewage spikes in the ocean water may lead to increased illness from airborne infection, did your study include an analysis of weather and temperature factors?
The county: This was not a study. This was an investigation of a report of increased GI illnesses. The first step in any investigation is to confirm the report. By comparing information from cases and non-cases the source of the illness may be identified.
The number of people reporting GI illness was not unusual, there were a variety of exposures including those unrelated to flooding or beach exposure and a mix of different pathogens as would be expecting in an urgent care.
Q: For example, were prevailing breezes during the two weeks in February offshore or onshore? And wouldn’t lower water and air temperatures in winter affect the potential for airborne transmission?
The county: This was not a study on airborne transmission.
Q: If you did not analyze those factors, how could you arrive at any findings of significance?
The county: Again, this was routine public health investigation into complaints received from a particular clinic. Public health has a long track record of disease investigation… Public Health also works closely with hospitals, including those in the South County, to monitor unusual trends in illnesses, which are often the first sign that something may be going wrong.
Q: It is unclear which specific facilities in Imperial Beach and the South Bay you reached out to for data beyond the South Bay Urgent Care. In a public health clinic, how significant are findings from a two-week study of medical records from a single health clinic?
The county: We surveyed nearby medical providers in the same area who reported no unusual upticks in gastrointestinal diseases when the concerns were initially raised in August of 2023. To get a better sense of data for entire region, including South region hospitals and zip codes, the county is able to monitor syndromic surveillance and compare data year to year to observe subtle changes. In addition, the County monitors key diseases, like Shigella, that is found in wastewater for increases in the South region and specifically, Imperial Beach zip codes. These entities are readily available on our website.
Q: Are there plans for further studies from the county or that the county is aware of in their communication with the California Department of Public Health?
The county: Public Health Services looks forward to working with the new task force on the long-term investigation of health effects from the sewage and other contaminants in the beach water and Tijuana River Valley. As an agent of the California Department of Public Health, we have also asked CDPH to seek support from CDC and have been working with CDPH to provide information and advocate for more focus on the sewage related health concerns in South Bay.
