Report on Botulinum Neurotoxin-Producing Clostridia
Authors: Botulinum Neurotoxin-Producing Clostridia Working Group on 
Published: September 2023

In 1992 a working group of the UK Advisory Committee on the Microbiological Safety of Food presented a report on Vacuum Packaging and Associated Processes regarding the microbiological safety of chilled foods. The report supported subsequent guidance provided by the UK Food Standards Agency for the safe manufacture of vacuum packed and modified atmosphere packed chilled foods. In 2021 the ACMSF requested that a new subgroup should update and build on the 1992 report as well as considering, in addition to chilled foods, some foods that are intended to be stored at ambient temperatures. The new subgroup agreed a scope that includes the conditions that support growth and/or neurotoxin formation by C. botulinum, and other clostridia, as well as identification of limiting conditions that provide control. Other foodborne pathogens that need to be considered separately and some foods including raw beef, pork and lamb were explicitly excluded. The subgroup considered the taxonomy, detection, epidemiology, occurrence, growth, survival and risks associated with C. botulinum and other neurotoxin-forming clostridia. There has been no significant change in the nature of foodborne botulism in recent decades except for the identification of rare cases caused by neurotoxigenic C. butyricum, C. baratii and C. sporogenes. Currently evidence indicates that non-clostridia do not pose a risk in relation to foodborne botulism. The subgroup has compiled lists of incidents and outbreaks of botulism, reported in the UK and worldwide, and have reviewed published information concerning growth parameters and control factors in relation to proteolytic C. botulinum, non-proteolytic C. botulinum and the other neurotoxigenic clostridia. The subgroup concluded that the frequency of occurrence of foodborne botulism is very low (very rare but cannot be excluded) with high severity (severe illness: causing life threatening or substantial sequelae or long-term illness). Uncertainty associated with the assessment of the frequency of occurrence, and with the assessment of severity, of foodborne botulism is low (solid and complete data; strong evidence in multiple sources). The vast majority of reported botulism outbreaks, for chilled or ambient stored foods, are identified with proteolytic C. botulinum and temperature abuse is the single most common cause. In the last 30 years, in the UK and worldwide where a cause can be identified, there is evidence that known controls, combined with the correct storage, would have prevented the reported incidents of foodborne botulism. The subgroup recommends that foods should continue to be formulated to control C. botulinum, and other botulinum neurotoxin-producing clostridia, in accordance with the known factors. With regard to these controls, the subgroup recommends some changes to the FSA guidelines that reflect improved information about using combinations of controls, the z-value used to establish equivalent thermal processes and the variable efficacy associated with some controls such as herbs and spices. Current information does not facilitate revision of the current reference process, heating at 90°C for 10 minutes, but there is strong evidence that this provides a lethality that exceeds the target 6 order of magnitude reduction in population size that is widely attributed to the process and the subgroup includes a recommendation that the FSA considers this issue. Early detection and connection of cases and rapid, effective coordinated responses to very rare incidents are identified as crucial elements for reducing risks from foodborne botulism. The subgroup recommends that the FSA works closely with other agencies to establish clear and validated preparedness in relation to potential major incidents of foodborne botulism in the UK.