Most readers will be aware of the recent outbreak in New Zealand of Yersinia pseudotuberculosis which has caused a number of cases of gastroenteritis.  For those of you overseas readers a brief overview – from September 1 – October 14 there were 289 notified cases of Yersiniosis of which 189 have been confirmed (to date) as Y. pseudotuberculosis and 49 confirmed as Y.enterocolitica and the other 58 as unknown species at this stage.  This compares with 13 cases in a “normal” year for NZ.  The suspected source but unconfirmed at this point seems to be prepackaged lettuce supplied to various supermarkets throughout the country.

So, lettuce find out more about Yersinia pseudotuberculosis ….

In animals other than humans (usually mammalian or avian hosts), the organism can cause tuberculosis type symptoms such as localised tissue necrosis and granulomas in the spleen, liver and lymph nodes (hence the name).  In humans, it generally mimics appendicitis (due to mesenteric lymphadenitis) with right sided abdo pain, fever and sometimes a rash and unlike Y.enterocolitica there is often an absence of diarrhoea making it sometimes difficult to diagnose.   Genetically, the organism is very similar to Y.pestis and it is believed that the plague evolved from Y.pseudotuberculosis anywhere from 1500 to 20,000 years ago.  It has previously been named Pasteurella pseudotuberculosis and Shigella pseudotuberculosis.

Symptoms usually appear 5-10 days post exposure and last between 1-3 weeks without treatment.  In severe cases or those in the immunocompromised, treatment options include Ampicillin, Aminoglycosides, 3rd generation Cephalosporins or Tetracycline. (In the NZ outbreak, 57 of the cases ended up being hospitalised).  Post infection complications include erythema nodosum and reactive arthritis.  Mortality rates are very low with the disease however if it presents in patients with chronic liver disease then the mortality rate increases up to 75%.  There is also a strong link between Y.pseudotuberculosis and Kawasaki Disease.