Waterborne epidemics may be widespread, affecting thousands of people or more.
Epidemics are more often encountered in areas where the water plants distribute groundwater as compared to areas where surface water is used, because small water plants do not necessarily disinfect groundwater like surface water.
A local committee should be established for the investigation of food poisonings and waterborne infections, including representatives from food and health protection authorities. Food poisoning, see Food Poisoning.
Find out about local epidemiology of waterborne epidemics, including number of events and most common pathogens causing them.
The quality of drinking water and the requirements concerning the monitoring of water plants and of the water itself are typically defined in legislation. Find out about local legislation and, for the EU, see also http://environment.ec.europa.eu/topics/water/drinking-water_en.
Drinking water distributed by water plants is monitored by taking water samples for chemical, microbiological and physical analyses regularly.
In the EU countries, presence of E. coli and enterococci are used as microbiological indicators of contamination. A 100 ml sample should be free of these bacteria.
If the above-mentioned bacteria are found in samples, control samples must be taken and necessary repair and protective actions have to be carried out jointly with the water plant without delay.
Causes of waterborne epidemics
The most common causes of waterborne epidemics are insufficient or lacking treatment of water, or contamination of drinking water by pathogenic faecal microbes originating in humans or warm-blooded animals, or both. The latter is often caused by runoff of rainwater into groundwater in association with heavy rains, or breaking of sewer pipes.
The most common pathogens causing epidemics in Northern Europe include noroviruses and Campylobacter.
Other noteworthy microbes include astro-, rota-, adeno- and enteroviruses as well as bacteria like Yersinia enterocolitica, E. coli, Salmonella, Shigella and Aeromonas.
When taking samples from travellers, also parasites should be taken into account, mainly Giardia intestinalis, Entamoeba histolytica and Cryptosporidium.
Toxins of fungi and moulds may rarely cause allergic or toxic general or respiratory symptoms transmitted by drinking or bathing water.
Actions to be taken in verified or suspected waterborne epidemics
Assessment
Check and follow local guidance, usually available by national or regional authorities.
A waterborne epidemic most often is discovered only when the first cases of the disease are found.
Measures to stop the epidemic must be taken immediately in the early stages of suspicion, even if evidence of a waterborne epidemic is not yet available.
Use the relevant national or regional reporting system, if available.
Key measures to stop a waterborne epidemic
Informing consumers about the contamination of domestic water
Restrictions on the use of domestic water and/or issuing a boil water advisory
Alternative water supply if necessary
Intensified analysis of water samples to determine the cause of the epidemic
Analysis of patient samples to identify the pathogen
Initiation and/or intensification of disinfection of domestic water
Elimination of the cause of contamination of domestic water
Laboratory investigations and differential diagnosis
Water samples are collected to identify both the causative agent and the indicator bacteria.
Check information from local health protection authorities for detailed guidelines on collection and transport of the water samples.
In an epidemic, samples have to be taken from several, for example from 10 ill people for the following investigations:
For the above-mentioned bacteria faecal bacterial tests, i.e. nucleic acid detection testing and, if positive for some bacteria, their culture, as well as appropriate testing for Clostridium perfringens, Bacillus cereus and Staphylococcus aureus
Faecal tests for viruses, for example a nucleic acid detection test for norovirus, as well as antigen detection test for rotavirus and adenovirus. Some laboratories have test packages available.
Based on consideration, testing for parasites (microscopy, nucleic acid detection).
In the differential diagnosis, take into consideration food-borne infections, as well as different types of gastroenteritis spreading via droplets or contact.
Reporting
Follow the local regulations and instructions concerning the reporting of suspected and verified waterborne epidemics in your area.