Unseen threats lurking in the water: Antibiotic resistance in recreational water and the vital role of risk assessment in protecting human health

Uncovering the hidden threat: Antibiotic resistance and health crises

Antibiotic-resistant bacteria in recreational water can cause infections harder to treat. Risk assessment is vital to protect human health from these threats.

Antibiotic resistance (AR) occurs when bacteria and microorganisms become resistant to the effect of antibiotics, leading to infections that are harder to treat. Natural aquatic environments such as surface and groundwater are predominantly susceptible to AR due to a residual concentration of metals, antibiotics, and peptides released from various sources of contamination. This can lead to the selection and proliferation of antibiotic-resistant bacteria (ARB) and facilitate the transfer of resistance genes between different bacterial populations. 

Scientists have reported that surface water, including ponds, wells, lakes, rivers, and oceans, contains a concoction of antibiotics, ARB and non-antibiotic-resistant bacteria (non-ARB), and other pathogens, which can act as a hotspot for resistance and invite the formation of new resistant bacteria. Surface water is a common destination for recreational activities such as swimming and bathing in many countries. It can also serve as a potential exposure source for humans to ARB and cause difficulty in treating future bacterial infections and hence, more extended hospital stays. It will also add extra cost to the already overburdened healthcare system and make the treatment procedure more costly for the commoner. 

As per se the Lancet report (2019), at least 1.27 million people die yearly due to AR. This number could rise to 10 million deaths annually by 2050 if action is not taken to address the problem, such an alarming increase.

What Could Be The Correct Course Of Action To Tackle This Situation?

Scientists are investigating different ways to tackle AR. A few of them include: developing new antibiotics, improving diagnostic techniques, avoiding overuse and misuse of antibiotics, and studying bacterial behaviour and evolution. One convenient way to prevent recreational hazards is to calculate human health risks and avoid future infections.

Although a complete protocol for estimating human health risks from exposure to ARB in recreational water is not yet available, existing literature-based concentration values of the bacteria can be utilized as an interim measure until a more robust protocol is developed. Using this approach, we developed a human health risk assessment framework to estimate accidental ingestion of ARB from recreational water during swimming.

Human Health Risk Assessment For ARB

Our study aimed to determine the risk of getting sick from AR E. coli while swimming in contaminated water. E. coli was selected as it comes under the critical priority AR pathogens category and poses a potential human health risk, as the World Health Organization (2017) reported in the Global Antimicrobial Resistance Surveillance System. Similarly, different classes of antibiotics (ampicillin or amoxicillin, co-trimoxazole, tetracycline, ceftriaxone or cefotaxime or ceftazidime, ciprofloxacin or ofloxacin) were selected as per the global antibiotic consumption and their resistance levels towards E. coli

Framework for risk assessment
Figure 1. Framework for risk assessment
Credit. Adapted and modified from the Journal of Environmental Management

We used previous research to develop a framework that helped us calculate the ratio of AR E. coli to total E. coli in the water. This ratio allowed us to determine the AR and non-AR bacteria concentration in the water. It was found that the risk of getting infected (annual risk of infection, 95th percentile =1) was higher than the recommended safe level (1/10,000), regardless of the class of antibiotics and chosen dose-response model. We also calculated the highest safe concentration values for the bacteria (AR E. coli (0.0075 CFU/dip) and non-ARB (2.56 CFU/dip)) in the water. And discovered that it was lower than the current guidelines (≀126 CFU/100 mL) set by the United States Environmental Protection Agency (USEPA). This suggests that the guidelines may need to be reviewed.

Can A Swimmer Go From Being Healthy To Unhealthy, And If So, How Likely Is It?

Conversion probability depends upon various factors (Figure 2), such as the health status of the GI tract of the individual (healthy or patient) as well as the AB concentration, horizontal gene transfer (HGT), self-immunity, and conversion/ mutation of non-ARB to ARB.

robability of conversion of a healthy individual to a non-healthy individual (patient) after ingestion of recreational water containing AR and non-AR E. coli
Figure 2. Probability of conversion of a healthy individual to a non-healthy individual (patient) after ingestion of recreational water containing AR and non-AR E. coli
Credit. Journal of Environmental Management

Where Else Can Risk Assessment Be Used?

It can be used for food safety, occupational and environmental health, pharmaceuticals, and public health emergencies. For example, it helps to recognize health hazards in the workplace, evaluate the safety of drugs and medical devices, and estimate the likelihood and severity of health threats. Risk assessment is essential for protecting human health and developing strategies to manage potential health hazards.


The accuracy of assessing the risk to human health from ARB in recreational water depends on factors such as comprehensive information about ARB and non-ARB, separate highest safe concentration values for different types of bacteria and a reliable dose-response model. Accurately assessing the risks associated with exposure to these bacteria in recreational water is complex and challenging. 

However, these challenges are minor, and the framework explained here is a valuable tool for assessing the risk associated with exposure to ARB in recreational water. This information can inform decision-makers about whether to close a pool, issue health warnings or take other measures to reduce the risk of exposure. By proactively managing the risk of ARB in recreational water, we can help save lives and protect public health. 

This exercise requires cooperation and collaboration between regulatory agencies, scientists, and the public. With ongoing research and continued vigilance, we can work towards a safer and healthier future for all.

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Journal reference

Tyagi, N., & Kumar, A. (2021). Evaluation of recreational risks due to exposure of antibiotic-resistance bacteria from environmental water: A proposed framework. Journal of Environmental Management279, 111626. https://doi.org/10.1016/j.jenvman.2020.111626

Dr. Neha Tyagi is a Lead Consultant at Rebound Envirotech Pvt Ltd in India, with over a decade of experience in water and wastewater treatment. Prior to joining Rebound Envirotech, she worked as an Assistant Professor at the National Institute of Technology (NIT) Jalandhar, India, and as a Postdoctoral researcher at the Indian Institute of Technology (IIT) Delhi. Dr. Tyagi holds a Ph.D. from IIT Bombay and a Master of Technology from NIT Jaipur, where she was awarded a gold medal for her academic performance. She is a senior member of IEEE and has research interests in producing value-added products, the fate of emerging contaminants, quantitative microbial risk assessment, and sustainable bioeconomy-based business models.