Human botulism is rare in France but levels have remained stable in recent years, according to a study.

Botulism is a notifiable disease in the country through a case-based passive surveillance system. All reports of human botulism are recorded by health authorities through Santé Publique France and cases are confirmed by the National Reference Center for Anaerobic Bacteria and Botulism.

The analysis has a focus on 2008 to 2018 for human botulism. Findings were published in the journal Frontiers Public Health and also cover animal botulism.

Botulism is a rare but life-threatening condition caused by toxins produced by Clostridium botulinum bacteria. In foodborne botulism, symptoms generally begin 18 to 36 hours after eating contaminated food. However, they can start as soon as six hours after or as long as 10 days later.

Symptoms can include general weakness, dizziness, double vision, and trouble speaking or swallowing. It paralyzes respiratory muscles so most patients must be placed on life support. Difficulty breathing, weakness of other muscles, abdominal distention and constipation may also occur. People experiencing these problems should seek immediate medical attention.

Outbreaks and links to food
The yearly number of cases and outbreaks of foodborne botulism remained stable in the 10 years studied. The annual number of outbreaks ranged from three to 13 and cases per year from four to 25.

A total of 82 outbreaks were foodborne from 2008 to 2018. These affected 159 people. The maximum number involved in a single outbreak was six.

In 2011, a tapenade of green olives sold commercially sickened six people. In 2010, dry-cured ham, which was home-prepared, led to six cases.

Four outbreaks were recorded in 2018. Home-prepared canned lentils and vegetable soup both affected one person each. Home-prepared canned French beans sickened two people and canned ratatouille led to four cases.

Type B was responsible for 53 outbreaks and 106 cases of foodborne botulism and type A for 15 outbreaks and 30 cases. Types E and F caused two outbreaks each involving four and five cases, respectively. This data was unknown for 10 outbreaks.

Identification of contaminated food was possible in 41 outbreaks. The most common items involved in outbreaks were canned foods and homemade products. The two main sources were raw ham and canned vegetables. Three composite foods, i.e., smoked fish, salted fish and ground (minced) meat, were also the source of outbreaks.

“Our study has shown that human botulism is mostly due to ham (pig sector) and canned vegetables, indicating the importance of the collection of surveillance data from the food industry, animal sectors as well as surveillance of this pathogen in the environment,” said researchers.

Situation in Switzerland
Meanwhile, the Federal Office of Public Health (OFSP) in Switzerland revealed that 29 foodborne botulism cases have been recorded from 1987 to 2022. One case was also reported in January 2023.

An outbreak, which included 12 cases and was linked to raw ham eaten at a party, occurred at the end of 1993 in Valais.

OFSP reported on the procedures to follow when investigating botulism cases, including declaration, diagnosis, and ordering antitoxin. While no Swiss laboratory analyzes botulism samples using the mouse bioassay, they can be sent to labs in France or Germany. This test is needed in clinical cases as detection of the toxin is necessary for diagnosis.