Download 2012 ANSWER KEY Disease Detectives Purdue University

ANSWER KEY
Disease Detectives
Div. C
Purdue University
Science Olympiad Regional Tournament
Saturday, February 25th, 2012
Names: _____________________________________
______________________________________
School: ______________________________________
Team Number: ______
Definitions:
Define the following terms.
1. Epidemiology (4 pts)
The study of the distribution / spread (1 pt), determinants / contributors(1 pt), and deterrents /
preventative factors(1pt) of disease/health-related condition(1pt)
2. Zoonosis (3pts)
Any infectious disease that can be transmitted from humans to animals or vice versa.
3. Risk (3pts)
The probability (1pt) that an individual will be affected by, or die from, an illness or injury (1pt)
within a stated time or age span (1pt)
4. Pathogenicity (3pts)
The capacity that an agent has to cause disease in a host.
5. Odds Ratio (3pts)
A method for measuring association between a cause and an effect (1pt). Used in case-control studies
(1pt). Defined mathematically as the odds of exposure among cases divided by the offs of exposure
among controls (1pt). (AD/BC on 2X2 table).
6. Epidemiology may be broken down into several subtopics. State one of the narrower areas of study
within epidemiology (2pts).
Many possibilities including classical epidemiology, clinical epidemiology, infectious disease
epidemiology, and chronic disease epidemiology (see Wikipedia page on epidemiology for many other
possibilities).
Problem Set 1 (questions 7-15):
A high school recently had a large number of students call in sick with gastrointestinal symptoms which
appear to be from food poisoning. The administration is beginning to worry that this may be an
outbreak, so they called in public health officials (including you) to help.
7. What extra information do you need to gather to decide whether or not this is a real problem worth
investigating? (4pts)
Verify the diagnosis (2pts)—are there any lab test results to support that an infectious agent in the food
that the students ate to support the diagnosis?
Confirm the outbreak using descriptive epidemiology (2pts)—examine endemic rates for gastrointestinal
diseases, look for additional cases, gather additional info about the ill patients, etc.
8. Public health officials use three types of information to characterize an outbreak known as the
epidemiological triad. What are these three pieces (3pts)?
Agent, Host, Environment (3pts), if students say person, place, time  give 2 pts
9. Besides an outbreak, what factors could cause a sudden increase in the number of cases of a specific
disease reported? Your answer does not have to relate to this case described above, it could relate to
any suspected outbreak. Explain two possible reasons. (4pts). 2 pts per reason
Possible answers include:
--Increased awareness of the diagnosis (doctors more likely to diagnose disease)
--Increased availability of new or more sensitive laboratory tests
-- Increased testing
--Increased reporting
--Change in denominator (total population of interest)- ex: when vacationers come to a resort area
--Change in the disease reporting system
--Laboratory error (lots of false positives) –especially important if one lab in town completes a significant
majority (or all) of the tests
10. You and your team have determined that this situation can be classified as an outbreak and it is
worth investigating. Define an outbreak and give the 10 recognized steps of an outbreak investigation
(hint: you may have already complete some of these steps) (13 pts).
Outbreak= suddenly more cases of a particular disease than expected in a given area or among a
specialized group of people over a particular period of time (3 pts)
Ten steps for investigating an outbreak (1pt/step):
1. Prepare for field work
2. Establish the existence of an outbreak
3. Verify the diagnosis
4. Define and identify cases
5. Describe and orient the data in terms of person, place, and time
6. Develop hypothesis
7. Evaluate hypothesis
8. Refine the hypothesis and carry out additional studies/collect more data
9. Implement control and prevention measures
10. Communicate findings
11. After surveying the students, you have concluded that the students contracted a food-borne disease.
The following data was collected regarding the foods that the 27 sick students ate at the high school
cafeteria during a 24 hour period prior to feeling ill and displaying symptoms. 462 students ate food
from the cafeteria during the investigated time frame. Calculate the attack rates for each of the foods
(6pts).
Food Consumed
Sloppy Joe
Chicken Salad
Sandwich
Steamed Vegetables
Apple Slices
Snickerdoodle Cookie
Ham and Cheese
Sandwich
Number of ill students
who consumed food
3
22
Number of healthy students
who consumed food
104
61
13
14
23
3
184
156
330
246
Attack rate
2.80%
26.5%
6.60%
8.24%
6.52%
1.20%
12. For the food with the highest attack rate, draw a 2X2 table used to quantify association. Please
include a total column and total row (hint: your table will actually be 3x3). (4 pts)
1 pt for choosing chicken salad sandwich—if another food is chosen, but the calculations are correct, the
students may still receive those points. 3pts for table—2 pts for main boxes, 1pt for totals
CHICKEN SALAD SAND.
Exposed
Not Exposed
Total
Ill
22
5
27
A
C
Not Ill
61 B
374 D
435
Total
83
379
462
13. What type of analytic study is being conducted in this outbreak (3 pts)?
Case-control study
14. Conduct the appropriate risk ratio for the 2x2 table above (3 pts). What conclusion can you draw
from your results (3pts)?
Odds Ratio (1pt)
OR= odds of exposure among cases/odds of exposure among controls=AD/BC
OR=(22*474)/(61*5)=34.2
(2pts)
Conclusion: An odds ratio of 34.2 means that a student who ate a chicken salad sandwich at this high
school cafeteria during the time period of the outbreak was 34.2 times more likely to become ill than a
student who did not eat a chicken salad sandwich (3pts)
15. One important aspect of public health is prevention of the spread of disease. What are four different
ways that a food-borne outbreak like this one could be avoided (4 pts)? 1 point per explanation
--Store foods at proper temperature and conditions
--Do not store raw meat with vegetables or other foods
--Clean all utensils, cutting boards or surfaces, etc. between uses on different foods
--Wash hands thoroughly/wear gloves while preparing/handling food
--Check temperatures of refrigerators and freezers according to FDA recommendations
--Do not handle food if you are ill
--Avoid cross contamination of foods
--Cook foods thoroughly
--Wash produce well before cooking or eating
Other answers may be acceptable.
16. Which type of descriptive or analytical study has a retrospective design in which subjects are
sampled by disease status and can also be used to investigate rare diseases? (3pts)
a. ecological study
b. cross-sectional study
c. retrospective cohort study
d. case-control study
e. none of the above
17. Which type of descriptive or analytical study can be either retrospective or prospective and is often
used when public health officials are investigating rare exposures? (3pts)
a. ecological study
b. cross-sectional study
c. cohort studies
d. interventional trials
e. prevalence studies
f. none of the above
18. You and your disease detective co-workers are on a trip to Guatemala where there has been an
increase in the number of cases of dengue fever. Dengue fever is caused by a virus that is spread by
mosquito vectors. Describe three prevention strategies that you would suggest to help control the
spread of the infection. (hint: think primary, secondary, and tertiary prevention) (6pts)
Student MUST discuss 1˚, 2˚, and 3˚ prevention. 2 pts per explanation. Possible answers may include:
Primary prevention: avoid initial exposure to dengue fever by trying to eliminate mosquito
vectors
Secondary prevention: screen/test and institute treatment for possible cases to try to prevent
progression to the symptomatic disease
Tertiary prevention: when patients show symptoms, induce interventions (treatments) that may
arrest, slow, or reverse the progression of dengue fever
Problem Set 2 (Questions 19-21) refers to the following report published May 7th, 2009 in Morbidity and
Mortality Weekly Report.
Outbreak of Salmonella Serotype Saintpaul Infections Associated with Eating Alfalfa Sprouts --- United
States, 2009
On February 24, 2009, the Nebraska Department of Health and Human Services identified six isolates
of Salmonella serotype Saintpaul with collection dates from February 7--14. Salmonella Saintpaul is not
a commonly detected serotype; during 2008, only three Salmonella Saintpaul isolates were identified in
Nebraska. This report summarizes the preliminary results of the investigation of this outbreak, which has
identified 228 cases in 13 states and implicated the source as alfalfa sprouts produced at multiple
facilities using seeds that likely originated from a common grower. On April 26, the Food and Drug
Administration (FDA) and CDC recommended that consumers not eat raw alfalfa sprouts, including
sprout blends containing alfalfa sprouts, until further notice. On May 1, FDA alerted sprout growers and
retailers that a seed supplier was withdrawing voluntarily from the market all lots of alfalfa seeds with a
specific three-digit prefix.
Initial Outbreak Investigation
For this investigation, a case was defined as illness in a person whose stool culture on or after February
1, 2009, yielded Salmonella Saintpaul with the outbreak strain pulsed-field gel electrophoresis (PFGE)
patterns (XbaI JN6X01.0072, JN6X01.0252, JN6X01.0340, JN6X01.0709, JN6X01.0712, JN6X01.0718, or
JN6X01.0719). During January 1, 2008 to January 31, 2009, only four cases of the outbreak strain
ofSalmonella Saintpaul were identified by PulseNet.
After a nationwide notice was sent February 26 to state public health officials about a cluster of cases
of Salmonella Saintpaul infection among Nebraska residents; additional cases were reported from Iowa,
Kansas, Minnesota, Missouri, and South Dakota. Interviews showed that five of 14 Nebraska patients
patronized a common restaurant chain (chain A) and that nine had recently eaten alfalfa sprouts. Among
the first seven Iowa case-patients interviewed, one had eaten at restaurant chain A, and six had eaten
alfalfa sprouts. Alfalfa sprouts was the most common food item reported.
To determine if a particular food item or restaurant was associated with this outbreak, health officials in
Nebraska and Iowa conducted a case-control study. They attempted to identify two controls for each
case; a well spouse or partner of the case-patient, and a well friend or colleague of the same sex and
similar age as the case-patient. Food consumption histories, including restaurants patronized, were
collected from case-patients for the 10 days before symptoms began and from controls for the matching
period.
Thirty-two confirmed cases and 32 controls were enrolled. Case-patients were significantly more likely
to have eaten alfalfa sprouts than matched controls (27/32 versus 5/32). No other food item was
significantly associated with illness. Case-patients were significantly more likely to have eaten at
restaurant chain A than were controls (24/32 versus 10/32), but this association was not statistically
significant after adjustment for exposure to alfalfa sprouts.
By March 19, a total of 186 cases had been identified in Illinois, Iowa, Kansas, Minnesota, Nebraska, and
South Dakota. Of the 156 patients with completed interviews, 114 (73%) reported alfalfa sprout
consumption.
Linking Cases to a Single Seed Grower
Tracebacks from the initial outbreak investigation indicated that although the sprouts had been
distributed by various companies, all originated at the same sprouting facility in Omaha, Nebraska
(facility A). Of the 114 patients with reported alfalfa sprout exposure, 112 (98%) could be linked to a
restaurant or a retail outlet that had received alfalfa sprouts from facility A. On March 3, 2009, facility A
agreed to conduct a voluntary recall.
Facility A produces several types of sprouts, including alfalfa, clover, radish, broccoli, and onion, and
distributes those to locations within a 250-mile radius. Facility A reported that it produced sprouts
following FDA guidance for reducing microbial food safety hazards for sprouted seeds. This included
soaking alfalfa seeds for 15 minutes in a 20,000 ppm chlorine solution derived from calcium
hypochlorite. The seeds were then rinsed and placed in germination containers; after 48 hours, seed
irrigation water was cultured for Salmonella and Escherichia coli O157. The facility reported that it had
no positive test results during January--February 2009.
An evaluation of records correlated the outbreak with the distribution of sprouts from a seed shipment
that arrived at the facility on January 13, and last sprouted on February 13. Multiple seed lots,
purchased only from seed company B, were used for producing alfalfa sprouts during the period of the
outbreak; all seed lots were identified with the prefix 032, indicating that they originated from the same
seed grower (grower C). A sample of facility A alfalfa sprouts collected from a Nebraska restaurant on
February 28, 2009, grew Salmonella serotype Typhimurium. A sample of alfalfa seeds collected at facility
A on March 3 and identified with the lot prefix 032 grew Salmonella serotype Give.
In mid-April, 42 additional case-patients with onset of illness beginning after March 15 were identified
from Florida, Iowa, North Carolina, Michigan, Minnesota, Nebraska, Ohio, Pennsylvania, Utah, and West
Virginia. At least 20 of these case-patients reported recently eating sprouts. Alfalfa sprouts eaten by
these case-patients were traced back to growing facilities in Michigan, Minnesota, and Pennsylvania that
received seed lots identified with prefix 032 from seed company B. Alfalfa sprout irrigation water
collected on March 10 from a growing facility in Wisconsin grew Salmonella Saintpaul indistinguishable
from the outbreak strain. These sprouts also were grown from a seed lot identified with prefix 032
received from seed company B. No human illnesses have been linked to the Wisconsin facility.
Preliminary findings indicate that the implicated seed lots were sold in many states and might account
for a large proportion of the alfalfa seeds that were being used by sprout growers during this outbreak.
Since February 1, a total of 228 cases have been reported from 13 states: Nebraska (110 cases), Iowa
(35), South Dakota (35), Michigan (18), Kansas (eight), Pennsylvania (seven), Minnesota (five), Ohio
(three), Illinois (two), West Virginia (two), Florida (one), North Carolina (one), and Utah (one). Patients
range in age from <1 year to 85 years (median: 29 years); 69% are female. Among patients with available
information, 4% reported being hospitalized. No deaths have been reported.
On April 26, FDA and CDC recommended that consumers not eat raw alfalfa sprouts, including sprout
blends containing alfalfa sprouts, until further notice. On May 1, FDA notified sprout growers and
retailers that seed company B was withdrawing voluntarily from the market all alfalfa seeds bearing sixdigit lot numbers that start with 032.
Editorial Note:
Raw and lightly cooked sprouts have been recognized as a source of foodborne illness in the United
States since 1995. In 1999, FDA released guidance to help seed producers and sprout growers enhance
the safety of their products. Specific measures recommended in the guidelines include seed disinfection
and microbiologic tests of water used to grow sprouts.
Although the methods recommended by FDA appear to reduce the risk of sprout-related human illness,
CDC's electronic Foodborne Outbreak Surveillance System has reports of 13 Salmonella and three E.
coliO157 outbreaks linked to sprouts from 2000 through 2007. Process failures, including inadequate
disinfection, sampling, and testing procedures, and incorrect interpretation of test results, have been
identified in some of these investigations.
The outbreak described in this report is linked to consumption of alfalfa sprouts produced at several
sprout growers and appears to involve only seeds sold by seed company B that originated from grower
C. This strongly suggests that the seeds were contaminated. The degree to which the various sprout
growers involved have appropriately and consistently implemented FDA recommendations or other
protective methods is under investigation. These outbreaks might indicate a need to determine how
well this important but voluntary guidance is being implemented. Additional studies of measures to
prevent, detect, and eliminate contamination of seeds and sprouts also are needed.
Alfalfa seeds might become contaminated in several ways, although the exact method is unknown.
Possible methods include preharvest contamination from use of contaminated water, the use of
improperly composted manure as fertilizer, fecal contamination from domestic or wild animals, runoff
from animal production facilities, and improperly cleaned harvesting or processing equipment. Seeds
also might become contaminated during conditioning, distribution, or improper storage. Many alfalfa
seeds are produced for agricultural use, and might not be processed, handled, and stored under
conditions appropriate for human food. Conditions suitable for sprouting also are ideal for markedly
increasing counts of bacteria that might be present on seeds. Unsanitary conditions during processing,
storage, distribution, handling, or preparation of sprouts could exacerbate the problem.
Since 1999, CDC and FDA have recommended that persons at high risk for complications of infection
with Salmonella and E. coli O157, such as the elderly, young children, and those with compromised
immune systems not eat raw sprouts. While investigations into the current outbreak continue, and until
more specific recommendations or control measures can be implemented, FDA and CDC recommend
not eating raw alfalfa sprouts, including sprout blends containing alfalfa sprouts. FDA recommends that
any sprouts that are eaten should be cooked thoroughly.
19. Construct a 2x2 table and calculate the odds ratio relating the consumption of alfalfa sprouts to
contracting the Salmonella infection (4 pts).
Ill
Not Ill
Exposed
27
5
Not Exposed
5
27
Odds Ratio= (27*27)/ (5*5)= 29.2 (2 pts for table, 2 pts for odds ratio—if table is incorrect, but the
students calculated the odds ratio correctly off their data, they can still earn up to 2 pts)
20. In your own words, state the case definition for the 6 initial cases of this infection which triggered
the full investigation (4pts).
Must be in own words, but basically must restate the following information:
--For this investigation, a case was defined as illness in a person whose stool culture on or after February
1, 2009, yielded Salmonella Saintpaul with the outbreak strain pulsed-field gel electrophoresis (PFGE)
patterns (XbaI JN6X01.0072, JN6X01.0252, JN6X01.0340, JN6X01.0709, JN6X01.0712, JN6X01.0718, or
JN6X01.0719). --> LAB-CONFIRMED SALMONELLA SAINTPAUL (1pt)
--Contracted disease in early Feb 2009 (time—1pt), Nebraska (place—1pt)
--Associated with alfalfa sprout consumption (1pt)
21. What are three ways alfalfa seeds may become contaminated with microbes? (At least one of your
explanations must be original.) (6pts) 2 pts per explanation
--preharvest contamination from use of contaminated water
-- the use of improperly composted manure as fertilizer
-- fecal contamination from domestic or wild animals
-- runoff from animal production facilities
-- improperly cleaned harvesting or processing equipment
-- Seeds also might become contaminated during conditioning, distribution, or improper storage
--Conditions suitable for sprouting also are ideal for markedly increasing counts of bacteria that might
be present on seeds. Unsanitary conditions during processing, storage, distribution, handling, or
preparation of sprouts could exacerbate the problem.
--Other explanations suggested by students will be accepted as long as the ideas seem reasonable
22. One way that epidemiologists display information about outbreaks are epidemic curves. Epidemic
curves can be useful to depict the extent of an outbreak. What are three other uses of an epidemic
curve? (6pts) 2pts per explanation; answers may include:
--Evaluate the pattern of spread
--Determine what kind of exposure has occurred (ex: person-to-person or point source)
--Time of exposure
--Compare to other similar outbreaks
23. Describe the type of outbreak that each of the following epidemic curve depicts (3pts). 1pt each
a.
point source
b.
person-to-person OR propagated source
c.
continuous common source
TIE-BREAKERS
State the cause of the disease (ex: virus, bacteria, etc.)
a. botulism bacteria
d. Q fever bacteria
b. giardia parasite
e. African trypanosomiasis protozoa
c. rabies virus
f. Japanese encephalitis virus