Question

Part II – Descriptive epidemiology and hypothesis generation

Staff members from the local health department where the terminal stop of the bus route was located were invited to participate in the investigation.

In addition, physicians attending to the cases of botulism were asked to provide demographic and clinical information on their patients. (Table 1)

In addition to identifying the most likely time period of exposure, the hypothesis-generating interviews with cases and other bus drivers, identified eating at the terminal home of the route as the only common exposures among cases. No cases of botulism occurred among bus drivers from the afternoon or evening shift of the route. Bus drivers from those shifts did not usually eat at the terminal home because it was only open for lunch. The investigators thus, hypothesized that the outbreak was limited to individuals eating or drinking something at the home at the terminal stop of the particular bus route between January 3 and 7.

Question: Based on a review of the data presented in Table 1, what type(s) of study would you use to investigate this hypothesis? Justify your choice.

Table 1: Characteristics of cases of botulism, Montevideo, January 1994 Patient Work shift Onset of neuro- Age No.(years) Gender logic symptoms Symptoms 42 Morning blurred vision, double vision, drooping eyelids, upper and lower extremity weakness, respiratory difficulty, fatigue January 6 blurred vision, double vision, drooping eyelids, upper and lower extremity weakness 31 Morning January 5 23 blurred vision, drooping eyelids, upper extremity weakness, fatigue Morning January 9 46 Morning January 8 drooping eyelids, difficulty speaking blurred vision, double vision, drooping eyelids, difficulty speaking, respiratory difficulty 54 Morning January 5 49 blurred vision, drooping eyelids, difficulty speaking Morning January 10 blurred vision, double vision, drooping eyelids, upper and lower extremity weakness, respiratory difficulty, fatigue 31 Morning January 15 respiratory difficulty, fatigue, drooping eyelids Morning January 14 24 Morning January 12 drooping eyelids, fatigue *M-male gender

Answer 1

Either cohort or case-control study can be used in order to explore this hypothesis.But Cohort study seems to be more appropriate as the outbreak affects small and a particular group of individuals.

Even studies like testing of food samples in particular study group in this case can be used,In addition to these studies,for testing this hypothesis Environmental investigations can also be undertaken