Diarrhoeal incident response protocol for public swimming pools and spa pools that use chlorine without cyanuric acid

Recommended remedial steps

1. Immediately close the affected pool and any other connected pools within the public swimming pools and spa pools and ensure staff involved in the response have appropriate personal protective equipment.
2. Remove as much of the faecal material as possible using a bucket, scoop or another container that can be discarded or easily cleaned and disinfected. Dispose of the faecal material in the sewer. Do not use vacuum cleaners for removing faecal material unless the vacuum waste can be directly discharged to the sewer and the vacuum equipment can be adequately cleaned and disinfected.
3. Adjust and maintain the pH to 7.5 or lower.
4. Hyper-chlorinate the affected pool by dosing the water to achieve a free chlorine C.t value of 15,300 mg.min/L for 3‑log₁₀ inactivation of Cryptosporidium, where C.t value = chlorine concentration mg/L x contact time in minutes.
   
   For example, raise and maintain free chlorine of 20 mg/L for 13 hours, or 10 mg/L for 26 hours, or via an alternative combination of chlorine concentration and time that achieves the required C.t value. Shorter contact times that meet the required C.t value to inactivate Cryptosporidium can be achieved if hyper-chlorination includes the combination of chlorine and chlorine dioxide, see table below:

Free chlorine and chlorine dioxide concentrations and contact time combinations for 3‑log₁₀ inactivation of Cryptosporidium ¹

Chlorine dioxide concentration (mg/L)	Free chlorine concentration (mg/L)	Contact time	pH
0	20.0	12 h 45 min	7.5
1.4	3.6	4 h 54 min	7.6
5.0	2.6	1 h 45 min	7.5

1. Adapted from Murphy et al. 2014.
5. Ensure that filtration and any secondary disinfection systems operate for the whole decontamination process.
6. If the filtration system incorporates a coagulation step, ensure the coagulant concentration is correct to enhance the filtration process.
7. After the hyper-chlorination process is complete, reduce the total chlorine to below 10 mg/L. Sodium thiosulfate can be added to neutralise excess chlorine.
8. Backwash filter media or replace the filter element as appropriate. Precoat filter media should be replaced.
9. Ensure the water is balanced.
10. Hygienically clean, disinfect or dispose of materials, tools, equipment or surfaces that have come into contact with contaminated water.
11. Record the incident and remedial action taken.
    
12. Re-open the pool.

For more information on diarrhoeal incident risk management of public swimming pools and spa pools, contact your local Public Health Unit on 1300 066 055 for advice.

Reference

Murphy, J.L., Haas, C.N., Arrowood, M.J., Hlavsa, M.C., Beach, M.J. & Hill, V.R., 2014. Efficacy of chlorine dioxide tablets on inactivation of Cryptosporidium oocysts. Environmental Science and Technology, 48, 5849-5856. doi: 10.1021/es500644d.