Yersinia

(endorsed 1996)

Guideline

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

General description

The genus Yersinia is currently placed in the family Enterobacteriaceae and comprises seven species. Strains of Y. enterocolitica can cause gastrointestinal disease if ingested.

A special feature of Y. enterocolitica and Y. enterocolitica-like organisms is their ability to grow at temperatures as low as 4°C. Accordingly, long survival of these organisms in water habitats can be demonstrated. For example, Y. enterocolitica was detected in distilled water for over 18 months at 4°C. Such long survival makes it difficult to find the origin of contamination.

Many domestic and wild animals are considered to be possible reservoirs of Y. enterocolitica, due to the high isolation rates of the organism from such sources. Wild animals, particularly hares and foxes, are probably a source of the bacteria, and swine have been implicated as a source of serotypes involved in human infections. The major vehicle of transmission is probably food, especially meat and meat products, milk and dairy products (Lloyd 1983). While Y. enterocolitica has also been isolated from a variety of environmental samples, especially from water, the isolated serotypes differ from those associated with human disease.

Ingestion of contaminated food and water is probably the most likely route of transmission of Y. enterocolitica. Direct transmission from person to person and from animals to people also occurs, but its relative importance has not been clarified. Further research is needed to define the epidemiological importance of ‘environmental’ strains of Y. enterocolitica.

Australian significance

The prevalence of notified cases of Yersinia infection varies between states. There has been a marked increase in the number of cases recorded in South Australia in recent years.

Treatment of drinking water

Standard disinfection procedures are sufficient to avoid transmission of Yersinia, provided the water has a low turbidity when treated. Free chlorine in the range required for water disinfection (0.2–0.5 mg/L) for 10 minutes at pH 7 completely eradicates the bacterium. Ozone eradicates the organism after contact with 0.05 mg/L for 1 minute, regardless of pH.

Method of identification and detection

Y. enterocolitica is a Gram-negative rod, motile at 25°C but nonmotile in cultures grown at 37°C (APHA Method 9260K 1992).

Health considerations

Some serovars of Y. enterocolitica are human pathogens. Atypical strains within Y. enterocolitica, isolated most frequently from environmental samples, are separated as Y. enterocolitica-like organisms. They are not pathogenic for humans and can be subdivided into Y. intermedia, Y. fredereksenii, Y. kristensenii, and Y. aldovae by biochemical means.

Yersiniosis generally presents as an acute gastroenteritis with diarrhoea, but other human diseases caused by Y. enterocolitica are also known. Y. enterocolitica may be waterborne.

Derivation of guideline

Water samples yielding Y. enterocolitica often show only light coliform contamination. One study indicated that 25% of Y. enterocolitica-positive samples were negative for both total and thermotolerant coliforms. Other studies showed a close relation between faecal pollution and Y. enterocolitica isolation rates. As it is not possible, at this stage, to determine an infectious dose, Y. enterocolitica should be absent from drinking water supplies.

References

APHA Method 9260K, (1992). Detection of pathogenic bacteria: Yersinia enterocolitica. Standard Methods for the Examination of Water and Wastewater, 18th edition. American Public Health Association, Washington DC.

Lloyd B (1983). Yersinia and yersiniosis. In: Feachem RG, Bradley DJ et al. (eds). Sanitation and disease: Health aspects of wastewater management. Chichester, John Wiley and Sons, pp 327–330.

Microorganisms

Protozoa