Laboratory diagnosis in a large outbreak of type A botulism: confirmation of the value of coproexamination.

Coproexamination is a vital component of the laboratory evaluation of botulism and is an essential part of the investigation of suspected botulism cases. In April 1978, type A botulism developed in 34 persons who had eaten at a restaurant in a town in New Mexico. Pretreatment serum specimens, along with stool specimens for toxin assay and culture for Clostridium botulinum, were obtained. At least one specimen (serum or stool) was available for each patient. Of 30 serum specimens, 16 (53%) were toxin positive; seven (32%) of 22 stools were toxin positive; and C. botulinum type A was cultured from 19 (79%) of 24 stool specimens. Overall laboratory confirmation was available for 26 cases (76%). Serum and stool toxin detection was related both to the time elapsed between symptom onset and specimen collection and to the severity of illness, with shorter times and severe illness associated with higher rates of toxin detection. Recovery of C. botulinum type A did not vary appreciably according to these factors. In 18 cases, both serum and stool specimens were available; the proportion of suspected cases that could be laboratory-proven increased by 46% when patients' feces, and not just their sera, were subjected to botulism testing procedures.