A trio of studies cover different outbreaks in Japan

Three recently published studies have detailed foodborne botulism and Campylobacter outbreaks in Japan.

The first, published in the Emerging Infectious Diseases journal, covered an outbreak of botulism in 2021 caused by Clostridium botulinum in Kumamoto.

A meal eaten in a domestic residence was the suspected cause, and four patients were affected. Botulinum toxin and Clostridium botulinum were detected in three of four specimens. A commercially prepared chicken dish was the likely cause, but no food was left for testing.

Clostridium botulinum is divided into groups I-IV, and botulinum neurotoxins (BoNT) are classified into seven types: A to G. Human botulism is caused primarily by toxin types A, B, and E, and human infections with Clostridium botulinum group III, which produces toxin types C and D, are rare.

Only five foodborne outbreaks due to Clostridium botulinum group III have been recorded, and in Japan, only one infant botulism case caused by type C has been reported.

Analysis of the isolated strain in the outbreak revealed it had the bont/C gene and was slightly different from the reference bont/C gene. Researchers said this gene had not been previously reported and proposed its designation as a new subtype of Clostridium botulinum toxin.

“The risk for human infection with this new toxin type should also be investigated in future research. However, given that human infections with a similar toxin type, Clostridium botulinum group III, have rarely occurred, this new toxin type might pose little threat to human health,” said scientists.

Second outbreak

Another study published in the same journal presented a case of Bacillus subtilis bacteremia in a patient who ate a traditional dish.

Genotypic methods showed the bacteria in a blood sample, and the ingested natto were the same strains. Natto, a traditional fermented food in Japan, is prepared by adding Bacillus subtilis natto to soybeans and fermenting them.

A 65-year-old man with cancer was admitted to Oita University Hospital with a fever and lower abdominal pain. He had a history of eating natto. Two months before admission, he began chemotherapy. After more than two months, the patient was discharged from hospital.

Two other natto brands and the one the patient reported consuming were tested. Analysis revealed two natto brands contained different bacterial strains. Many brands are sold in Japan; each uses different soybean cultivars, processing conditions, and Bacillus subtilis natto strains. Researchers said a history of natto consumption alone might not be associated with the cause of Bacillus subtilis bacteremia because eating the product is not uncommon. 

Scientists said as the popularity of Japanese cuisine is increasing worldwide, clinicians elsewhere should be aware of Bacillus subtilis bacteremia caused by natto consumption.

“Our case and others in the literature indicate that older or immunocompromised patients who consume natto are at risk for serious infection. Clinicians should advise patients in these risk groups to avoid eating natto or food products containing Bacillus subtilis bacteria.”

Campylobacter and raw milk

The third study, published in the journal Foodborne Pathogens and Disease, detailed Campylobacter outbreaks linked to raw milk.

In August 2018, there were three outbreaks of campylobacteriosis, likely caused by the consumption of unpasteurized raw milk from the same farm.

Researchers analyzed Campylobacter jejuni isolates obtained at the three locations using several methods.

Whole genome sequencing (WGS) and single nucleotide variant (SNV) analysis provided evidence indicating that contamination was attributed to the farm. Scientists said findings suggest that SNV analysis provides molecular biological support in cases with sufficient epidemiological information. Similar analytical methods may be used in other sporadic cases to determine their relevance.

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