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Problem Statement
Problem Statement
San Diego county is known for its abundance of beautiful, sunny beaches. As one would expect, beach tourism encompasses a large portion of its annual visitors. In fact, over one million people visited San Diego’s beaches over the 2024 Fourth of July weekend alone. The number of beach visitors rises year by year, and with it, the risk of contracting waterborne illnesses. An estimated 57 million people in the United States alone get sick annually due to swimming in contaminated water. These numbers pose the threat of a potential significant public health crisis.
Our project aims to study the pollution levels of four types of bacteria–E. Coli, Enterococcus, Fecal Coliforms, and Total Coliforms–at different San Diego county beaches. In completing this project we aim to help inform individuals of the dangers of each form of bacterial infection, minimize their potential of serious harm, and provide recommendations on which beaches are the safest to visit throughout the year.
Water Quality Standards
Water Quality Standards
Methods for Sampling Bacteria
Methods for Sampling Bacteria
Using Title 17 of the California Code of Regulations as a guideline1, we defined our thresholds for considering a beach to be safe as the following (in most probable number - MPN):
For single samples:
E. Coli: 100 MPN/100 mL
Enterococcus: 105 MPN/100 mL
Fecal Coliforms: 400 MPN/100 mL
Total Coliforms: 10000 MPN/100 mL
For monthly means:
E. Coli: 50 MPN/100 mL
Enterococcus: 35 MPN/100 mL
Fecal Coliforms: 200 MPN/100 mL
Total Coliforms: 1000 MPN/100 mL
Any reading above these thresholds are, for the purposes of our study, considered to be unsafe for swimming; it would be our recommendation to close the beach. Any reading under is considered to be safe and swimmable.
Membrane Filter (MF)
Membrane Filter (MF)
In our data, the MF method was used to sample for Enterococcus, Fecal Coliforms, and Total Coliforms, but it has been known to see use in sampling for E. Coli as well. The process is summarized below2:
Pour a water sample through a filter and draw all liquid from the filter using a vacuum, leaving behind only the bacteria.
Incubate in a petri dish. Colonies of bacteria remain to be counted.
Colilert 18
Colilert 18
Colilert 18 is used to find various types of coliforms in a sample. In the instance of our study, it was used to sample both E. Coli and Total Coliforms. This process is also summarized below3:
Add a reagent to a sample and leave it to incubate for 18 hours.
Results are presented in the form of a shade of yellow: a solid yellow indicates the presence of Total Coliforms, while a more fluorescent yellow indicates E. Coli.
To explicitly find the MPN in a sample, the sample is divided between multiple test tubes. The number of yellow tubes is then referenced with an MPN table.
Enterolert
Enterolert
The Enterolert method is used to sample Enterococcus bacteria. The process closely resembles the Colilert 18 method for detecting bacteria and determining MPN, although the incubation time is 24 hours instead of 18.4
Dangers of Bacterial Infection
Dangers of Bacterial Infection
Escherichia Coli (E. Coli)
Escherichia Coli (E. Coli)
Escherichia Coli (E. Coli) is among the most dangerous if ingested while swimming. According to the CDC, when a person becomes infected, the possibility of diarrhea, urinary tract infections, sepsis, and other illnesses opens up.5 Although these are serious symptoms that would typically require medical attention, among the most deadly is Hemolytic Uremic Syndrome. This condition sometimes involves kidney failure and can potentially lead to death. People may even develop a chronic version of the disease, leading to long-term, or even permanent, health complications.6
Enterococci
Enterococci
Enterococci are bacteria found in coastal waters, often as a byproduct of fecal waste. This bacteria survives well in saltwater, making it a common occurrence at beaches.7 This specific bacteria can cause infections of the skin, eyes, and ears, and can even affect the respiratory tract. Enterococci can be very difficult to treat due to its aggression and high resistance to numerous antibiotics. Among the most common ailments caused by Enterococcus infections are urinary tract infections (UTI); every year, Enterococcus infections contribute around 110,000 cases in the United States.8 Alongside UTIs, this bacteria can cause open wounds that may lead to a need for chronic surgery and medical treatment. Furthermore, once this bacteria is in the bloodstream, people can experience numerous symptoms such as fever, nausea, and rashes.
Total (and Fecal) Coliforms
Total (and Fecal) Coliforms
Total coliforms refer to a large group of different types of bacteria, divided into two subgroups: fecal and non-fecal.9 Fecal coliforms include several types of bacteria, most notably E. Coli. These bacteria only grow in the presence of fecal waste and when there is an increase in temperature. People infected with fecal coliforms can experience nausea, cramps, headaches, and other symptoms.10 Although these are curable, a weaker immune system targeted by these bacteria, such as those of the young and elderly, can experience lethal symptoms.
Repercussions Beyond Public Health
Repercussions Beyond Public Health
As much of a risk as bacterial infections pose to the human body, they have also been found to affect areas beyond general public health, especially the economy. The United States alone is estimated to see four billion annual recreational water events. From these events, an estimated 90 million people contract water-borne illnesses, ultimately costing around $2.2-3.7 billion in productivity loss, doctor and hospital visits, and prescriptions.11 In fact, in Los Angeles and Orange counties alone, around 627,800 to 1,497,200 excess gastrointestinal illnesses are contracted each year, resulting in a loss of $21-51 million.12
The nature of the bacteria itself also plays a large role in these observed losses. As previously mentioned, Enterococcus is a dangerous bacteria due to its high resistance to antibiotics. According to the Institute of Medicine, the annual cost to treat symptoms caused by this bacteria, as well as others with high antibiotic resistance, is estimated to be around $4-5 billion. This affects the entire scope of the healthcare industry, from the large-scale pharmaceutical manufacturers to the individual physician, as well as the general public itself; the costs of making and searching for “different drugs and services, as well as for personnel time, supplies, space, and equipment for institutional programs“ rises tremendously.13
References
References
- State Ocean Water Quality Standard
http://www.publichealth.lacounty.gov/eh/safety/state-ocean-water-quality-standards.htm
- Membrane Filter Technique
https://www.membrane-solutions.com/news_80.htm
- About Escherichia coli Infection
https://www.cdc.gov/ecoli/about/index.html
- Signs of Hemolytic Uremic Syndrome
https://www.cdc.gov/ecoli/signs-symptoms/hus.html
- Indicators: Enterococci
https://www.epa.gov/national-aquatic-resource-surveys/indicators-enterococci
- Enterococcal Infections
https://www.webmd.com/a-to-z-guides/what-are-enterococcal-infections
- Total and Fecal Coliform Bacteria
https://jchealth.com/wp-content/uploads/2020/03/total-coliform-fact-sheet-1.pdf
- Estimate of incidence and cost of recreational waterborne illness on United States surface waters
https://ehjournal.biomedcentral.com/articles/10.1186/s12940-017-0347-9#
- Beach Pollution Effects on Health and Productivity in California
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6604031/
- Economic Impact of Antimicrobial Resistance
https://wwwnc.cdc.gov/eid/article/7/2/70-0286_article#
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