Slovakian botulism case linked to rare subtype in hummus

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A very rare subtype implicated in only one previous outbreak was responsible for a case of botulism in Slovakia, according to research.

In mid-August 2015, a healthy adult in their 40s consumed three packs (100g each) of a commercial hummus spread after obtaining it from a food bank.

The hummus, sold in Slovakia and the Czech Republic, had a best-before date of nine days after consumption.

A total of nine to 11 hours after consumption, the patient experienced nausea, vomiting, double vision, unsteady gait, dizziness, generalised weakness and difficulties swallowing and was admitted to hospital.

They were discharged from hospital after 78 days, but still had breathing problems as of the last follow-up in May 2017.

Botulism rareness

Testing labs should be aware that strains harbouring this rare subtype can occur in Europe and should validate methods accordingly, said researchers.

“The rareness and divergence of the BoNT/A3 subtype poses the risk that it might not be detected by immunological or sequence-based diagnostic assays that have not been validated against it. In fact, one ELISA has already been shown to be unable to detect it.

“Furthermore, in one of the four mentioned PCR methods in ISO ISO/TS 17919:2013, the sequence of one primer and the probe each contain one mismatch towards all BoNT/A3 sequences. These mismatches might therefore hamper identification of strains belonging to the A3 subtype by the corresponding PCR.”

Botulism is caused by seven serotypes (A-G) of botulinum neurotoxins (BoNT), however only serotypes A, B, E and F cause disease in humans. BoNTs can be destroyed by temperatures above 70 °C in minutes.

It is associated with marinated meat, fish, fruits, vegetables or mushrooms as well as home-canned products and home-cured or smoked meat or fish products consumed unheated.

Between 2010 and 2014 ECDC reported 492 cases in Europe.

Gas production but hummus tasted normal

Clostridium botulinum type A was isolated from three nearly empty hummus tubes.

Three strains with typical C. botulinum morphology were isolated, one from each tube. Two of them were PCR-positive for the bont/A gene.

The product, sold in Slovakia and the Czech Republic, was withdrawn and a warning was issued through the Rapid Alert System for Food and Feed (RASFF).

The interview of the patient and a close relative revealed one tube of hummus showed gas production prior to being opened, but it tasted normal according to the patient.

An investigation at the producing company revealed the hummus product consisted of: chick peas, tofu, rapeseed oil, onion, salt, maize starch and spices. It also found the chickpeas originated from Brazil or Argentina.

Three unopened hummus tubes with the same production date from a supermarket were subjected to 37 °C storage.

Microbiological analysis and PCR testing did not reveal C. botulinum or C. sporogenes despite signs of gas formation during storage.

“To our knowledge, this is only the second time that this subtype was involved in foodborne botulism since eight people died from contaminated wild duck paste in Loch Maree, Scotland in 1922,” said the researchers.

“No other strain belonging to this specific A3 subtype was isolated or subtyped for nearly a century until Lúquez and colleagues identified three strains from Argentina (in soil and salad) in 2012.

“Interestingly, the two described BoNT/A-positive isolates have an identical BoNT/A sequence at the amino acid level as one of the strains (CDC54054) isolated from Argentinian soil, and the chickpeas used in the hummus consumed by the patient originated from South America, either from Brazil or Argentina.”

Source: Eurosurveillance, Volume 22, Issue 32, 10 August 2017

Reoccurrence of botulinum neurotoxin subtype A3 inducing foodborne botulism, Slovaka, 2015

Authors: L Mad’arová, BG Dorner, L Schaade, V Donáth, M Avdičová, M Fatkulinová, J Strhársky, I Sedliačiková, C Klement, MB Dorner

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