“Plague? Why plague?” he asked.
“They’ve grown Yersinia and that causes plague… don’t you know that?” exclaimed the Junior Doctor
“What was the specimen sample type?” replied the Microbiologist, resisting the temptation to explain to the doctor just what he knows at some length!
“Hold on I’ll check…” said the doctor, “oh, it was a stool sample, and it says Yersinia enterocolitica isolated and that causes plague doesn’t it?”
“No, it doesn’t. It causes yersiniosis, which usually presents with diarrhoea or abdominal pain. Let me explain to you exactly what I do know…” said the Microbiologist finally giving in to temptation.
What is yersiniosis?
Yersiniosis is the term given to a group of infections caused by bacteria in the Yersinia spp. family. Yersinia spp. are facultatively anaerobic Gram-negative bacilli in the Enterobacteriaceae family (along with E. coli, Klebsiella spp. etc.). The most commonly isolated bacterium in the species is Yersinia enterocolitica followed by the much less common Y. pseudotuberculosis. There is another important Yersinia spp., Yersinia pestis, which is the one that causes plague, but the Bug Blog has covered this before so this time we’re going to concentrate on the other species.
Yersiniosis is a zoonotic infection; it is acquired from animals. In particular Y. enterocolitica is part of the normal flora of pigs, whereas Y. pseudotuberculosis has been isolated from numerous mammals and birds. The most common route of acquisition of yersiniosis is through eating raw or under-cooked pork meat or contact with food or water contaminated by pigs. Various food stuffs have been implicated including sausages, chitterlings (intestines) and even milk (from cows not pigs!) as well as tofu... though I don’t know how tofu gets contaminated, isn’t that meant to be vegan and nowhere near pigs!!? I digress…
How does yersiniosis present?
The incubation period for yersiniosis is usually between 3 to 7 days but can be as long as 10 days.
Yersiniosis presents with:
- Infectious diarrhoea, often associated with a fever and most common in children, with inflammation of the ileum (most distal part of the small bowel)
- Mesenteric adenitis, inflammation of the lymph nodes that are associated with the ileum, which can present with central and right sided abdominal pain and is a common differential diagnosis for appendicitis
- Reactive arthritis, with an inflamed joint due to an autoimmune reaction to the gastrointestinal infection rather than the actual source of infection being within the joint itself
- Systemic infection, very rare, and associated with bacteria growing in blood cultures; these are deep seated infections such as liver and splenic abscesses as well as occasionally infective endocarditis. Yersinia spp. will grow easily in blood cultures if the patient is septicaemic but this is a very rare occurrence because the type of clinical presentation is very rare.
Systemic infections are more common in patients who are immunosuppressed or who are iron overloaded e.g. from repeated blood transfusions, as the iron increases the virulence of the bacterium.
In the past yersiniosis was occasionally associated with blood transfusions. This was because if blood was taken from someone who had Yersinia spp. in their blood it would be able to continue to proliferate in the blood sample during its cold storage; when it was then given to the next patient there were large numbers of bacteria present. This is one of the reasons why there is a visual check of a blood transfusion bag before it is infused; if it is infected with Yersinia spp. it will look darker, dirtier and just wrong. There are still occasional cases of transfusion related yersiniosis which is why it is standard practice to send blood cultures from the patient and the residual infusion bag when a patient has a severe febrile reaction to a transfusion.
How is yersiniosis diagnosed?
The most common sample for diagnosing yersiniosis is a stool sample. Any sample where the clinical details suggest mesenteric adenitis, terminal ileitis or reactive arthritis should be cultured for Yersinia spp. This is an example where clinical details are critical otherwise the laboratory simply won’t do the test. Samples should be plated on to CIN agar (Cefsulodin irgasan [triclosan] novobiocin agar…microbiology…what a mouthful!), a selective agar for growing Yersinia spp. The CIN plate should then be incubated at 28-30 oC in air in order to exploit the difference in growth characteristics between Yersinia spp. and other bowel bacteria (e.g. E. coli, Enterococcus spp. etc.); Yersinia spp. will grow at the lower temperature whereas most others will not. An enrichment culture step with Tris-buffered 1% peptone (pH 8.0) for 24 hours prior to plating onto CIN can enhance Yersinia spp. isolation.
How is yersiniosis treated?
Infectious gastroenteritis yersiniosis is a self-limiting problem and does not require antibiotic treatment. Supportive care with fluids may occasionally be required.
However, septicaemia does need antibiotics, usually with a combination of a 3rd generation cephalosporin such as Ceftriaxone or Cefotaxime PLUS an aminoglycoside such as IV Gentamicin. The cephalosporin can be replaced with Ciprofloxacin in patients with a severe beta-lactam allergy. The minimum duration of therapy for septicaemia is 3 weeks although if an abscess or endocarditis is diagnosed then this will need to be extended to 4-6 weeks.
It is important to note that most Yersinia spp. produce a chromosomal beta-lactamase and are therefore resistant to Ampicillin, Amoxicillin and the 1st generation cephalosporins such as Cefalexin and Cefradine; Co-amoxiclav is also not effective in treating septicaemia.
How can yersiniosis be prevented?
Environmental exposure to Yersinia spp. can be prevented by safe handling of food and access to clean water; in particular making sure that any pork products are properly cooked before eating… so make sure those sausages are nice and hot on your barbeques and watch out for those sausages in the staff canteen!
In hospital anyone with diarrhoea should be managed with infection control precautions.
Hand Hygiene |
With soap and water or alcohol gel |
PPE |
Gloves and apron when coming into contact with body fluids Remove ALL PPE before leaving room |
Isolation |
Side room preferably with own toilet facility |
Staffing |
Symptomatic staff must not return to work until 48 hours after last episode of diarrhoea or vomiting |
Environmental decontamination |
Deep cleaning of the clinical area daily and after patient is discharged |
Patient care |
Accurate recording of symptoms Stool sample for testing under advice from ICT (infection control team) Do not prescribe anti-motility agents If patients require investigations in other departments, inform those departments of patient’s condition in advance Patient should be last on a list and deep cleaning commence after patient’s departure |