Yersiniosis

Prior to 2014, the vast majority of cases of yersiniosis in New Zealand were caused by Yersinia enterocolitica biotype 4 (commonly found in pigs in New Zealand). In 2014 Y. pseudotuberculosis isolates accounted for almost half of all notifications and Y. enterocolitica biotype 2 has become the most common biotype isolated in New Zealand.

More detailed epidemiological information is available on the Institute of Environmental Science and Research (ESR) surveillance website.

Further information on foodborne illness is available on the Ministry for Primary Industries website.

In children under 5 years old, Y. enterocolitica infection typically causes diarrhoea, vomiting, fever and occasionally abdominal pain. In contrast, older children and adults are more likely to experience abdominal pain as the prominent symptom. Bacteraemia and sepsis may occur in immunocompromised individuals. Y. pseudotuberculosis is more likely to cause mesenteric adenitis and septicaemia than Y. enterocolitica.

Laboratory definitive evidence for a confirmed case requires:

• isolation of Yersinia enterocolitica or Y. pseudotuberculosis from blood or faeces
• detection of Yersinia spp nucleic acid from faeces.[1]
• Serology does not meet the criteria for laboratory confirmation.

All isolates should be sent to the Enteric Reference Laboratory at ESR for further characterisation.

• Under investigation: A case that has been notified, but information is not yet available to classify it as probable or confirmed.
• Probable: A clinically compatible illness that is epidemiologically linked to a confirmed case or has had contact with the same common source as a confirmed case – that is, is part of a common-source outbreak.
• Confirmed: A clinically compatible illness accompanied by laboratory definitive evidence.
• Not a case: A case that has been investigated and subsequently found not to meet the case definition.

Animals. Pigs are the main reservoir for Y. enterocolitica; Y. pseudotuberculosis is widespread among many avian and mammalian hosts including deer.

From 3–7 days, generally under 10 days.[2]

Mostly through ingestion of contaminated food, including pork and pork products, dairy products (especially unpasteurised milk), fruit, vegetables and tofu.

Although optimal growth is seen at 28–30°C, Y. enterocolitica, like L. monocytogenes, also grows well in a refrigerator (4°C) and survives freezing.

In New Zealand yersiniosis is also associated with ingestion of untreated water, direct contact with an infected animal, and person-to-person spread. Person-to-person transmission in a hospital has been reported. Yersinia spp. have rarely been transmitted from asymptomatic patients by blood transfusion.

Y. pseudotuberculosis is thought to be distributed less widely in the environment than Y. enterocolitica but both are considered to be significant foodborne pathogens. Outbreaks caused by Y. pseudotuberculosis are rare, but they have been noted overseas where carrots, lettuces and milk were the vectors. While implicated in the 2014 Y. pseudotuberculosis outbreak, produce was not confirmed as the source of the outbreak. Infections from Y. enterocolitica are often linked to pork products and pigs are considered to be a major reservoir of human pathogenic strains. Y. pseudotuberculosis is also found in the gut of many wild and domestic animals and is considered one of the most serious and common infectious disease of deer in New Zealand.

Note that methods for detection of Yersinia spp. in foods are poor and hence attribution of human illness to specific foods is difficult.

Faecal shedding generally persists for 2–3 weeks but can be prolonged (months) in both children and adults.

Attending medical practitioners or laboratories must immediately notify the local medical officer of health of suspected cases. Notification should not await confirmation.

Obtain a food history, details of ingestion of untreated water, contact with animals, possible human contacts and travel.

In a health care facility, only standard precautions are indicated in most cases; if the case is diapered or incontinent, apply contact precautions for the duration of illness. For further details, refer to the exclusion and clearance criteria in Appendix 2: Enteric disease.

Advise the case and their caregivers of the nature of the infection and its mode of transmission. Educate about hygiene, especially hand cleaning.

All those with unprotected close contact with a case during the period of communicability or who have been exposed to the same contaminated food, water or other source in a common-source outbreak.

Test for asymptomatic infection only in an outbreak.

Advise all contacts of the incubation period and typical symptoms of yersiniosis, and to seek early medical attention if symptoms develop.

Check for other cases in the community. Investigate potential food or water sources of infection only if there is a cluster of cases or an apparent epidemiological link.

If indicated, check the water supply for microbiological contamination and compliance with the latest New Zealand drinking-water standards (Ministry of Health 2008).

Clean and disinfect surfaces and articles soiled with stool. For further details, refer to Appendix 1: Disinfection.

Educate the public about safe food preparation (see Appendix 3: Patient information).

Hand-cleaning facilities should be available and used after contact with animals. Young children should be supervised during contact with animals and during hand cleaning. Food-related activities should be separated from areas that house animals. Domestic animals with diarrhoea should be taken to a veterinarian for assessment and treatment.

If a water supply is involved, liaise with the local territorial authority to inform the public. Advise on the need to boil water.

In early childhood services or other institutional situations, ensure satisfactory facilities and practices regarding hand cleaning; nappy changing; toilet use and toilet training; preparation and handling of food; and cleaning of sleeping areas, toys and other surfaces.

Ensure complete case information is entered into EpiSurv.

Where food/food businesses are thought to be involved inform the Ministry for Primary Industries.

If a cluster of cases occurs, contact 0800GETMOH - CD option, and outbreak liaison staff at ESR, and complete the Outbreak Report Form.

• Ministry of Health. 2008. Drinking-water Standards for New Zealand 2005 (Revised 2008). Wellington: Ministry of Health.

[1] However, note that presently PCR testing may not detect Y. pseudotuberculosis and the ability of the assays to adequately detect of Y. enterocolitica biotype 1A is uncertain as of July 2017.

[2] CDC range, 1–14 days – see the CDC website.