Ministry for Primary Industries (MPI) has been notified by Environmental Science and Research of a cluster of human illnesses linked to the bacteria Yersinia pseudotuberculosis.

While cases are reported each year, there has been an increase in cases, mainly in Christchuch, Wellngton and Auckland, but reports have also come from the Bay of Plenty, Waikato,  Hawkes Bay and Otago/Southland.

There is a total of 101 confirmed cases and 41 presumptive (suspected but yet to confirmed) nationwide. A total of 38 people have been hospitalized.

The increase has been observed since mid-August with the majority of confirmed cases occurring in September.

Yersinia pseudotuberculosis causes stomach cramps and can present symptoms that mimic appendicitis. Diarrhea can occur but is rare. It has a 3 to 21 day incubation period.  Post-infectious complications can occur, such as reactive arthritis and erythema nodosum. The arthritic phase of the disease can last up to 6 months.

New Zealand/CIA
New Zealand/CIA

MPI is working to determine the source of the outbreak.

At this stage, the source has not yet been identified, but Yersinia pseudotuberculosis outbreaks overseas have been linked to contaminated fresh vegetables and fruit, contaminated water and animal contact. Consumption of contaminated foods (infections by pasteurized milk, chocolate milk, tofu, beans and home slaughtered pork have been reported) and water, as well as contact with infectious soil, can cause an infection.

More common in younger patients. In an outbreak in Finland due to contaminated lettuce, the median age of patients was 19 years old.  The number of infections peaks in late fall to spring and epidemics have been caused by contaminated food or water.

We believe there is a credible link that food is the likely source, but it is too early to be certain about the source of this pathogen and direct people away from foods that have no proven risk for consumers.

The people who have become ill with Yersinia have been interviewed on what foods they have been eating and this information has been cross-referenced, giving us sources to investigate further.

It is important to note that MPI’s investigation is over a range of foods.

Person to person spread is uncommon. For more infectious disease news and information, visit and “like” the Infectious Disease News Facebook page