Salmonella

(endorsed 1996)

Guideline

Escherichia coli (or alternatively thermotolerant coliforms) are used to indicate the possible presence of Salmonella spp. If explicitly sought, Salmonella spp. should not be detected. If detected, advice should be sought from the relevant health authority or drinking water regulator.

General description

Salmonella spp. are widely distributed in the environment and gain entry into water systems though faecal contamination from livestock, native animals, drainage waters and incompletely treated waste discharges.

Faecal contamination of water which is inadequately treated or inadequately disinfected is the main cause of waterborne outbreaks of salmonellosis.

Australian significance

Salmonella has been isolated from a number of source waters in Australia and occasionally from reticulated waters. However, published associations between the isolation of Salmonella from drinking water and health effects in the community are mainly anecdotal.

Most illnesses resulting from Salmonella infection are derived from contaminated foodstuffs, e.g. poultry and livestock. Waterborne Salmonella spp. play only a minor role in causing disease.

Treatment of drinking water

Treatment by disinfection using chlorine is usually effective against Salmonella spp., provided the water has low turbidity.

Method of identification and detection

The numbers of Salmonella in water can be determined by concentration followed by enrichment, isolation and confirmation (AS4276.14 2014).

Health considerations

Salmonella spp., with the exception of those that cause enteric fever in humans (Lloyd 1983), are pathogens of animals, which provide important reservoirs for the infection of humans.

Salmonella Typhi, however, is a specific human pathogen. In particular, S. Typhi, S. Paratyphi A, and S. Paratyphi B are able to invade tissues and cause a septicaemia with high temperature rather than diarrhoea. This is known as enteric fever. In humans, most of the other serovars cause a transient intestinal infection which results in acute gastroenteritis with diarrhoea. Certain serovars are highly pathogenic for humans, while others appear nonpathogenic. Many Salmonella infections are symptomless.

Epidemiological and volunteer studies show that the infective dose of Salmonella varies considerably. Method of intake, individual host susceptibility, and virulence of the particular strain are important in determining the dose required to produce an infection.

Waterborne outbreaks due to substantial contamination are usually characterised by rapid onset. The majority of cases develop over a period of a few days, and these may be followed by secondary cases. The spatial distribution of infections in major outbreaks is often strongly correlated with the water supply system.

Derivation of guideline

The presence of faecal indicator bacteria is useful to determine the possible presence of Salmonella spp. However, as with many other pathogens, Salmonella spp. may occasionally be present when indicators are absent, particularly where a supply may have been subject to faecal contamination by amphibians (frogs) and reptiles. It is also important, therefore, to test directly for Salmonellae if contamination is suspected.

The direct effect on the community of noncompliance with the guideline will depend on the Salmonella species involved. The numbers of Salmonella may be amplified through contamination of foodstuffs.

References

AS4276.14, (2014). Australian Standard. Water microbiology: Detection of Salmonella spp. Standards Australia, Sydney, NSW.

Lloyd B (1983). Salmonella, enteric fever and salmonelloses. In: Feachem RG, Bradley DJ et al. (editors). Health aspects of excreta and wastewater management. Chichester, John Wiley and Sons, pp 251–286.