Incubation period as a clinical predictor of botulism: analysis of previous izushi-borne outbreaks in Hokkaido, Japan, from 1951 to 1965

This study investigated 21 foodborne type-E botulism outbreaks, without antitoxin administration, from 1951 to 1965 in Hokkaido, Japan, to characterize the descriptive epidemiology and evaluate the relationship between case fatality and incubation period. The median (25-75% quartile) attack rate and case fatality, which were evaluated by outbreak, were 58.3% (38.0-73.2) and 25.7% (0.1-50.0) respectively. Individual records of 64 diagnoses, including 31 deaths, were also examined using logistic regression analysis, revealing that a shorter incubation period is likely to result in a significantly higher risk of death (P=0.01). The observed case fatality was more than 50% for those who developed symptoms within the first 18 h after exposure, possibly reflecting underlying dose-dependent mechanisms. In the event of intentional contamination of food with botulinum toxin, rapidly determining the incubation periods may be critical for guiding public health response efforts.