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Team number:_____________________
Disease Detectives division B
Mentor Invitational 2008
Total points______/ 85
Correctly match the following epidemiological terms in the left hand column with
the appropriate description, example or formula in the right hand column. Choose
the best answer. (2 points each)
A. habitat where the infectious agent normally lives, grows,
and multiplies
B. any mode or mechanism by which an infectious agent is
spread to a susceptible host
C. a person without apparent disease who is nonetheless
capable of transmitting the disease to others
D. constant low frequency of disease
E. acquired in a hospital
F. infectious diseases that are transmissible under normal
conditions from animals to humans
G. disease occurring in a population at a higher than normal
H. an epidemic which spreads over several countries or
continents and affects a large number of people
I. objects such as food, water, biological products and fomites
that may directly transmit an infectious agent from a reservoir
to a host.
J. the number or proportion of cases/events/conditions in a
given population at a given time
K. science concerned with the distribution and determinants of
health events in human populations
L. the systematic, ongoing collection, analysis, interpretation,
and dissemination of health data
M. various arthropods that transmit pathogenic organism from
one host to another
14.____mortality rate
N. number of new cases during a period divided by the total
15. ____ pandemic
O. deaths per total infected
Page 1
Norovirus Outbreak in an Elementary School --- District
of Columbia, February 2007
On February 8, 2007, the District of Columbia Department of Health (DCDOH) was
notified of an outbreak of acute gastroenteritis in an elementary school (prekindergarten
through sixth grade). The school nurse reported that 27 students and two staff members
had become ill during February 4--8 with nausea, vomiting, and diarrhea; because
symptoms lasted <48 hours, a viral etiology was suspected.
Epidemiologic Investigation
On February 9, DCDOH conducted a site visit and interviewed school personnel to
determine the possible etiology of and risk factors for illness and to recommend
additional control measures. The school had two to three classes per grade, and one to
three staff members were assigned to each class. Although students attended a few
classes outside their classroom each day (e.g., art or math), they spent the majority of
time in their own classrooms. No outbreaks of gastrointestinal illness in the community
were reported to DCDOH during this period.
A questionnaire was developed to use in a cohort study of all staff members and students.
Because no food was served at the school other than lunches that students brought from
home and prepackaged snacks served in prekindergarten classes, foodborne transmission
was not suspected; questions focused on illness onset, symptoms, school grade,
classroom, special classes (e.g., art), ill contacts, and use of certain facilities or equipment
(e.g., library computers) or participation in certain programs (e.g., after-school
programs). Questionnaires were sent home by the school principal with all staff members
and students the afternoon of February 9.
The school nurse identified additional cases beginning February 9 by visiting each
classroom daily; she interviewed persons who became ill during school and interviewed
absent ill persons or a family member by telephone regarding grade, classes, illness onset,
and symptoms. Information regarding ill contacts, facility and equipment use, and
participation in programs was unavailable from the participants enrolled by the nurse.
Of 314 students and 66 staff members at the school, 207 students and 59 staff members
participated in the DCDOH investigation, for a total of 266 participants. Of 266
participants, 103 met the case definition. Among the 103 ill persons, 79 were students
and 24 were staff members.
Reported symptoms included vomiting (64%), nausea (56%), and diarrhea (47%). The
median duration of illness was 36 hours (range: 0.2 to 96 hours). Median length of stay at
home after onset of symptoms was 1 day (range: 0--4 days).
Page 2
16. Write a case definition for this outbreak. (5 points)
17. Calculate the overall attack rate for those meeting the case definition. Round to the
nearest percentage. (3 points)
18. What percentage of the ill persons were students? (3 points)
19. What percentage of the ill persons were staff members? (3 points)
Laboratory Investigation
Stool-specimen collection kits were provided during the DCDOH site visit on February 9,
and specimens were received from two ill persons. Twenty-five swabs were used to
sample environmental surfaces. Although February 9 was the day after the initial bleach
cleaning, several surfaces had not been cleaned and were visibly soiled. Sampled surfaces
included toilets, faucets, water fountains, doorknobs, mice and keyboards from three
computers (each in a different room), school utensils, and toys. Samples were tested by
reverse transcription--polymerase chain reaction (RT-PCR) for norovirus and DNA
sequencing; stool specimens also were cultured for bacteria.
Laboratory results were available February 13. One (4%) of the 25 environmental swabs,
from a computer mouse and keyboard in first-grade classroom J, was positive for
norovirus subtype GII. Norovirus subtype GII also was identified in both stool
specimens. Noroviruses from the two stool specimens and a single environmental sample
were identical by DNA sequencing of region B, the gene commonly used for genetic
classification. Bacterial cultures of stool specimens and environmental samples were
Page 3
20. Based on the laboratory data, as noted above, what interventions would you
recommend to control this outbreak? (5 points)
21. Development of protective antibodies in a potential host through response to
infection or immunization. (1 point)
A. Herd immunity
B. Active immunity
C. Passive immunity
D. None of the above
Page 4
True or False (2 points each)
22._____ A cohort study is used in an outbreak setting when a complete list of
participants is available.
23. _____ The measure of risk used in a cohort study is the odds ratio.
24. _____ A cross-sectional study is basically the same as a survey. They are good
for examining the relationship between a variable and a disease, not for determining
cause and effect.
25. _____Latency period is the period of time from exposure to the onset of
26._____ A pathogen is an organism that is never found on a healthy person.
27. _____ The single most important way to stop the spread of infection or disease is
by performing good hand hygiene.
28. With most new infectious diseases, some human action is involved that changes
the environment so that an existing microbe may take up residence in a new niche.
Once that happens, a pathogen that had been confined to a remote habitat appears in a
new or wider region, or a microbe that had infected only animals suddenly begins
causing human disease.
List two human activities/actions that may have led to the emergence and spread of
new diseases. (6 points)
29. A ____ case has many factors that point to a diagnosis but may lack lab
verification. (1 point)
None of the above
Page 5
30. List the three main components to the epidemiologic triad. (3 points)
31. Antibiotics may be used to treat this type of pathogen. (1 point)
A and B
All of the above
32. Disease prevention is the key to public health. It is always better to prevent a disease
than to treat it. Vaccines prevent disease in the people who receive them and protect those
who come into contact with unvaccinated individuals. Vaccines help prevent infectious
diseases and save lives. Vaccines are responsible for the control of many infectious
diseases that were once common in this country. (5 points)
List 5 vaccine preventable diseases.
33. An epidemic curve: (1 point)
graphically displays the scope of an outbreak
shows the number of people affected by an outbreak
shows the course of the outbreak over time
all of the above
A and B
Page 6
34. An outbreak of diarrhea in a flood-hit city in central Mozambique has claimed the
lives of 64 people since early January 2008, the local council said on Tuesday [5 Feb
2008]. The municipal authority in the city of Tete said that a total of 835 people had
contracted diarrhea from contaminated water since the flooding began at the start of
2008. "64 of that total have not survived," the council's statement said.
What is the case fatality rate? Show the formula. (3 points)
Calculate the odds ratio given the following data.
Ate watermelon
Did not eat
35. What was the odds ratio of persons who ate watermelon and becoming ill? (3
A. 8
B. 15
C. 800
D. 62
Page 7
Tie Breaker #1
Match each disease with the causative agent (one point each)
Causative agent
36. _______________Lyme disease
37. _______________Smallpox
38. _______________Anthrax
39. _______________Giardiasis
40. _______________Legionnaires disease
41. _______________Trichinosis
42. _______________Rabies
43._______________Dengue fever
44._______________Chagas disease
45. ______________Creutzfeldt-Jakob
46. ______________Tuberculosis
47. ______________Kawasaki disease
Page 8
Tie breaker #2
48. List the 10 steps of an outbreak investigation. (10 points)
Page 9