Epidemics are more often encountered in areas where the water plants distribute groundwater as compared to areas where surface water is used, because groundwater usually needs not be disinfected unlike surface water.
A local committee should be established for the investigation of food poisonings and waterborne infections, including representatives from both health protection and health care authorities, as well as from the water supply and sewerage service. Food poisoning, see Food Poisoning.
Training for special situations forms an essential part in epidemic preparedness.
Monitoring drinking water
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. Since the end of the year 2003, all water distributed within the EU must meet these criteria.
If the above-mentioned bacteria are found in samples, control samples must be taken immediately. Simultaneously, necessary repair and protective actions have to be taken without delay.
Causes of water-borne epidemics
The most common causes of water-borne epidemics are insufficient or lacking treatment of water, 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 jejuni.
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 lamblia, Entamoeba histolytica and Cryptosporidium.
Toxins of 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 water-borne epidemics
Assessment
An epidemic must be verified which may be surprisingly difficult and time-consuming. The most common source of information concerning an epidemic or a suspicion of one are consumer complaints. When several cases of gastroenteritis occur concurrently in a limited area, the possibility of a water-borne epidemic should be borne in mind.
The assessment includes mapping of the situation, collection and investigation of samples, collection of epidemiological data from the patients and exclusion of other causes.
Mapping of the situation includes asking the municipal water supply and sewerage services and the construction sector about possible malfunction of the water treatment plant and about possible damages or change works in the water supply or sewer lines. Possible deviations in the results from water quality control samples are traced. The extent and limits of the epidemic area are established on the basis of the disease cases.
Preventing the spread of the epidemic
Informing the public is of utmost importance if there is a possibility that the epidemic is widespread, and in such a case even strong suspicion of an epidemic warrants community-level information. All means of communication should be utilized. If the epidemic is limited to a small area, handouts distributed to all houses can be used. The public should also be informed if the suspicion proves to be false and when the epidemic has ceased.
The announcements should include instructions of the possible need of boiling the drinking water. The boiling time should be at least 5 minutes.
It the epidemic is widespread or causes severe symptoms, health protection authorities may decide to prohibit the use of water according to the health protection act.
Rectifying measures
Treatment of household water is intensified and disinfection started in groundwater plants that do not already use it.
Technical defects like pipeline breakages are repaired.
Water distribution network is cleaned with so-called shock chlorinations and backwashings.
Laboratory investigations and differential diagnosis
Water samples are collected to identify both the causative agent and the indicator bacteria.
Health protection authorities have produced detailed guidelines on collection and transport of the water samples. The volume of the sample should be 12 litres per one sampling point which is much more than is required for standard water quality monitoring.
In epidemics, samples have to be taken from several, preferably from about 10 ill people for the following investigations:
bacterial stool cultures for the above-mentioned bacteria and for Clostridium perfringens, Bacillus cereus and Staphylococcus aureus
viral stool culture (to detect noro-, astro- or rotaviruses), electron microscopy of stools and rapid diagnostic viral tests (rota- and adenoviruses)
consider microscopic examination for parasites.
Take food-borne infections and poisoning, as well as viral infection spreading via personal contact, into consideration in the differential diagnosis.
Reporting
Follow the local regulations and instructions concerning the reporting of suspected and verified epidemics of food or water-borne infections in your area.