A group of tourists on a weeklong bus tour of a European country experienced an
outbreak of norovirus. The group had followed a consistent meal time pattern: each
morning they had breakfast together in whichever hotel they had stayed from 6:00 a.m.
to 7:00 a.m., stopped for lunch from 1:00 p.m. to 2:00 p.m., then had dinner together
either at the next hotel or at a restaurant at about 7:00 p.m. The incubation period for
norovirus is about 24-48 hours, with a median of about 33 hours. On which day and at
which meal was exposure most likely?
A. April 19 Dinner
B. April 20 Breakfast
C. April 20 Lunch
D. April 20 Dinner
E. April 21 Breakfast
17. Possible explanations for a case that occurs substantially later than the other cases in an
outbreak include:
A. Similar but unrelated disease
B. Secondary case
C. Case with unusually long incubation period
D. Time of exposure later than others
E. Error in recording date
18. A spot map is particularly useful for displaying:
A. Geographic location of exposure of each case-patient
B. Residence of each case-patient
C. Incidence rate of disease by area
D. Prevalence rate of disease by area
19. Which of the following may be useful in generating hypotheses in an outbreak setting?
A. Review the literature
B. Look at the descriptive epidemiology
C. Look at the outliers
D. Talk with the local health authorities
E. Talk with a few of the case-patients
F. Talk with subject matter experts