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Disease Detectives National Science Olympiad

May 2005

This event includes 3 Problems. Problem III is a tie breaker.

Problem I : Disease Detectives Attack the Public Health Problem of Monkeypox in Pets

Total suggested time = 15 minutes

Monkeypox is a disease that is found mostly in Africa. It is caused by the monkeypox virus. To see if an animal has monkeypox, scientists do blood tests to look for the virus. The first case was found in 1958, in laboratory monkeys. Other types of animals can also get monkeypox. Scientists have found monkeypox virus in African squirrels and in rats, mice, and rabbits. In 1970, the first case was reported in humans.

Monkeypox belongs to a group of viruses that includes the smallpox virus (variola), the virus used in the smallpox vaccine (vaccinia), and the cowpox virus. In people, monkeypox acts a lot like smallpox, only it is usually milder than smallpox. People start getting sick about 12 days after they are infected with the monkeypox virus. They get a fever, headache, muscle aches, and backache. Their lymph nodes swell, and they feel tired

One to three days (sometimes longer) after the fever starts, the infected person gets a rash. The rash often starts on the face and spreads, but it can also start on other parts of the body. The rash goes through several stages. First it develops into raised bumps filled with fluid. Later the bumps get crusty, scab over, and fall off. The illness usually lasts for 2 to 4 weeks.

An Outbreak ofMonkeypox in the United States

In 2003, there was an outbreak ofmonkeypox in the United States. By June 10, disease detectives had found a total of 53 cases ofmonkeypox. These were in Illinois, Indiana, and Wisconsin. Twenty-nine of the people who were sick were men. The gender of two was not known. Fourteen of the people were hospitalized.

Of the 5 3 people who were sick, 51 said they had direct or close contact with prairie dogs. One person had contact with a Gambian giant rat. One had contact with a sick rabbit that had been exposed to a sick prairie dog at a veterinary clinic. Everyone who got sick had contact with an animal. Two of the people also had contact with fluid from another person's sores.

Figure 1, on the next page, shows the number of cases by the date that symptoms began.

Point total this page _______ _

FIGURE 1. Number' of persons with monkeypox, by date of first symptom onset -Illinois and Wisconsin, May 1~une1o,2003

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1. a. (2pts) What do disease detectives call diseases that spread from vertebrate animals to people?

Zoonoses, zoonotic disease - vectorbome is a distinct entity - give 0.5 pt, none for mosquitobome

b. (4pts) Name two diseases besides monkeypox that are spread from animals to people. Examples include - 1 pt for each, 0 for disease not zoonotic.Rabies, leptospirosis, tularemia, plague, psittacosis, cat scratch fever , brucellosis, salmonellosis, tubersulosis, leprosy, listeriosis, borreliosis, Lyme disease, anthrax, blastomycosis, Q fever, West Nile, St Louis encephalitis, Yellow fever, hantavirus, toxoplasmosis, malaria, cryptosporidiosis, giardiasis

2. (2 pts) What proportion of the cases found by June 10 were females?

proportion females = (53-29-2)/53 = 41.5% or (53-29-2)/(53-2) = 43.3%

3. (2 pts) On what date did the outbreak seem to peak?

May 30, 2003. Accept May 30 or "between May 29 and May 31"

4. (2 pts) On what date was the first person to become sick most likely infected?

May 3, 2003 - accept May 3. , 0.5 pt for before May 15, 0 points for May 15, Note: First case had onset on May 15, Preceding paragraph states that symptoms start about 12 days after infection

Point total this page _______ _ 2

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Disease detectives knew that everyone who was sick as of June 10, 2003 had contact with animals. Even so, they wanted to find out if person-to-person transmission was possible. To do this, they needed to collect information from a different group of people. These people needed to have certain characteristics in order for disease detectives to determine if person to person transmission took place.

5. (4 pts) Describe two of the characteristics in this additional group of persons that disease detectives would have studied in order to determine if person to person transmission took place.

In order to demonstrate person-to-person transmission, disease detectives would want to collect information from persons who had contact with case after they became ill and who did not have contact with an infected animal

6. (6 pts) An important part of the disease detective's job is to stop an illness from spreading. Based on what you know so far, give three actions public health workers should recommend to keep more people from getting monkeypox.

• Avoid contact with newly purchased animals - especially those who are ill • Wash hands after contact with animals - changing cages, handling, etc • Do not bring healthy or previously owned animals into contact with ill animals or newly

purchased animals • Have all ill animals checked by a veterinarian - report possible cases to local health dept

The above are examples - accept any modification of these or reasonable alternative.

******* The CDC asked health workers, veterinarians, and public health officials to be on the lookout for monkeypox. If they thought an animal or a person had the disease, they were asked to report it to their state or local health department. CDC asked that these reports be sent on to them.

CDC also created three case definitions for monkeypox. One definition was for suspected cases. One was for probable cases. The last was for confirmed cases. These definitions were based on three kinds of information. The first was information about the signs and symptoms of the disease. This comes from doctors or other health care workers. The second kind of information is from laboratories . This information has to do with finding the virus in tissues of people with the disease. The third is epidemiologic information. This information is about how a person or animal was exposed to the illness.

7. (4 pts) Give two reasons why epidemiologists use case definitions.

Epidemiologists use case definitions in order to insure that cases all rea lly do have the condition of interest, to distinguish between those with the condition of interest and persons who may have other, similar, illnesses, to make sure that cases are alike with respect to the illness they have, to avoid counting well people or people with other illnesses as cases. The above are some examples - reasonable variations should all be accepted bu~ 11eed to address the concepts of true positives, true negatives, fa lse positives and false negatives. Complete and nonbiased representation of cases are also acceptable. Give only 1 pt if the two answers overlap - e.g. to make sure they get all the cases and to make sure they don't miss anyone.

Point total thi s page _ _ ___ _ _ _ 3

8. (3 pts) The disease detectives in this outbreak divided cases into three groups according to how likely it was that the cases were really monkeypox. List the three categories they would have used. Write them in decreasing order with the most likely category first and least likely last.

Confirmed, Probable, Suspect - must be in order - no credit for those not in order

******* People continued to get sick with monkeypox. By July 8, 2003, CDC knew of71 cases. Wisconsin had 39 cases. Indiana had 16 cases. Illinois had 12. Missouri had 2. Kansas and Ohio each had 1. Figure 2 shows these cases according to the date when people started having symptoms. ·

FIGURE 1. Number of monkeypox cases*, by date of illness onset - Illinois, Indiana, Kansas, Missouri, Ohio , and Wisconsin, 2003t

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t N = 69 of 71 cases with known date of illness onset. As of July 8, 2003.

Point total this page ______ _ 4

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9. (12 pts) What is the state-specific frequency distribution for the 71 monkeypox cases? Express your answer as percents.

State N % Wisconsin 39 54.9 Indiana 16 22.5 Illinois 12 16.9 Missouri 2 2.8 Kansas 1 1.4 Ohio 1 1.4

1 pt per state - need not have N if% given,

10. (6 pts) How many probable cases were reported as a result this outbreak? How many suspected cases? How many confirmed cases?

Probable cases 13 - - - -

Suspected cases 21

Confirmed cases 35 ---

11. (2 pts) What do disease detectives call graphs that show the number of cases according to the date that symptoms started?

Epidemic curve, epi curve, .5 pt for histogram

Point total this page _ _ _____ _ 5

Problem II: Disease Detectives Take On The Public Health Problem of Salmonellosis from Reptiles

Total Suggested time = I 5 minutes

Salmonellosis is an infection with bacteria in the genus Salmonella. This group was named after Dr. Daniel Salmon, an American veterinarian who first discovered it in 1885. There are many different kinds of Salmonella bacteria. The most common ones found in the United States are salmonella serotypes Typhimurium and Enteritidis. The symptoms of the illness are diarrhea, fever, and abdominal cramps. These usually begin 12 to 72 hours after a person is infected. The illness usually lasts 4 to 7 days. Most people get well without treatment. Sometimes the infection spreads from the intestines to the blood stream and then to other parts of the body. When that happens, a person must be hospitalized and treated with antibiotics right away. Otherwise, the person could die.

In January 1996, the laboratory at the Colorado state health department tested several stool samples from children living in Jefferson County, Colorado. They found an usual looking strain of Salmonella serotype Enteritidis. Health department disease detectives talked with the children and their families. They found one common link between the cases. All of the children had been to a 9-day exhibit ofKomodo dragons (Figure 1) at the local zoo. The exhibit opened for zoo members on January 11. It was open to the ge~eral publi'c from January 13 through 21.

Disease detectives investigated to find o~t if any more people had gotten sick. They also wanted to know how the disease had been transmitted.

Figure 1. Komodo dragon

Point total this page _______ _ 6

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1. (8 pts) Use the information on the previous page to develop a case definition for this outbreak.

A case is defined as a person who attended the Komodo dragon exhibit at the Jefferson County Zoo between January 13 and January 21, 1996 and who either developed diarrhea, fever, and abdominal cramps 12 to 72 hours after attending or who had a positive stool culture for Salmonella enteriditis

( 1 pt each for place, time, clinical symptoms and lab results, may give .5pt for less than complete criteria)

******* Disease detectives enrolled people in the study who met the definition for a confirmed case. However, they did not include those who attended the event on January 11. They also did not include anyone who became sick after someone else living in their household had become sick.

2. a. (2 pts) Sometimes, when one person in a household gets sick, other household members will get sick later. What do epidemiologists call this second group of people who get sick?

Secondary cases (1 pt for secondary attack rate)

b. (2 pts) Why would disease detectives not include these people in their study?

They were not included because they were most likely infected at different time/place than the people who attended the exhibit and collecting information from them would only confuse interpretation of results. Must have both aspects - different exposure and consequence of including them in analysis for full credit.

******* Disease detectives chose controls for their study at random from two groups of people. The first group was new and renewed zoo members for the month of January. The second group was zoo patrons who participated in the "adopt a Komodo Jragon" program. They matched controls to cases according to age group and the date that they went to the zoo.

3. a. (2 pts) Why did disease detectives match cases and controls by age and date of visit?

They wanted to make sure they were similar with respect to those two variables

b. (2 pts) How did this matching affect the disea~'.' detective's ability to detect differences related to age and date of visit in their analysis?

They were not able to look for differences in these two variables.

Point total this page _ _______ _ 7

******* Twenty six patients and 49 controls were enrolled in the study. Disease detectives talked with all of the patients and controls. They asked about personal characteristics like age and gender. They also asked about each person's medical history, what symptoms they had, and what they did at the zoo. Some of the results are shown in Table l.

Table 1. Activities engaged in by patients (ill persons) and controls (well persons) while at the Komodo dragon exhibit at the Jefferson County Zoological Gardens, number of persons reporting

exposure/number of persons answering a given question.

Number of Number of patients controls Odds

Exposure (Exposed/Total) (Exposed/Total) ratio p value

Touched dragon 0/26 2/49 0 0.8

Touched exhibit barrier 19/23 22/42 4.00 0.02

Touched display reptile skin 8/25 20/47 0.60 0.34

Touched computer display 12/25 22/49 1.13 0.82

Stood near barrier 22/26 36/48 l.98 0.29

Washed hands at zoo after visiting exhibit 2/25 18/49 0.14 0.02

Washed hands before next meal after visiting exhibit 3/22 26/49 0.10 0.004

Touched barrier, then washed hands at zoo or before next meal 3/19 12/22 0.22 0.05

Ate food from zoo concessions 16/26 23/49 0.98 0.96

Point total this page _______ _ 8

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4. a. (4pts) Which exposure listed in the table was the most likely to have caused this outbreak? What information in the table tells you this?

Touching the barrier because the odds ration is the greatest and p value is <0.05

b. (6pts) Which 3 exposures appeared to protect against illness? What information in the table tells you this?

Washing hands after visiting the exhibit (OR= 0.14, p =0.02) Washing hands before next meal after visiting exhibit ( Touched barrier, then washed hands at zoo or before next meal (give full credit" OR <I and p<0.05" give half credit for "OR< 1" or "pvalue < 0.05")

c. (2pts) What proportion of patients washed their hands after visiting the exhibit? Show your calculations.

2/(18+2) = 2/20 = 10%

d. (2 pts) Including both the patients and the controls, what proportion of visitors ate food from zoo concessions? Show your calculations.

= 26/(26+49) = 26175 = 33%

5. (2 pts) What is the usual way in which salmonella infections are transmitted?

fecal oral route, or some variation indicating portal of exit and portal of entry give . I pt for just feces or ingesting

6. (3 pts) Zoo officials will need to make changes to prevent ihis sort of outbreak from happening again. List three things you think they should do.

Do not let visitors come into contact with animals or barriers Clean and disinfect barriers periodically Provide handwashing facilities close to exhibit area;

Point total this page _______ _ 9

Problem III. Disease Detectives Battle the Spanish Flu (TIE-BREAKER)

Total Suggested time = 15 minutes

Please read the following scenario and answer the questions that follow.

Figure l: New York City Police Officers During Spanish Flu Pandemic

In the spring of 1918, a dangerous kind of flu broke out in the United States and in Western Europe. A second outbreak took place in the fall. The second outbreak is sometimes called the Spanish Flu. Many people became sick. As many as fifty million people may have died. In some areas, 50% of the people who got sick died. This is very high for an infectious disease. Both flu outbreaks may have begun in China.

People who got sick had high fever and high pulse and breathing rates. Their lips and face turned bluish-purple. Their lungs hemorrhaged and filled with fluid. The virus affected only lung tissue and upper respiratory tissues . It did not affect a person's entire system. People often died from lung failure and pneumonia in less than five days .

The virus involved is a form of type A flu virus. It can change rapidly. This ability to evolve has produced new strains of the virus on a yearly basis. Interestingly, people who recover from a given strain of the flu normally can not get that strain again. The virus is evolved from a bird flu virus. People can get it from infected pigs or directly from birds.

Point total this page _______ _ 10

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1. a. (2 pts) Figure l shows the number of deaths per l 00,000 population per year. Circle the portion of the graph representing increased number of deaths over the past one hundred years.

Figure l: Deaths per l 00,000 population per year, 1900-2000

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b. (2 pts) What event is this period of increased death rate associated with?

Spanish tlu epidemic, also 1918 tlu epidemic

c. (2 pts) Give the expected death rate during this time period if this increase had not happened.

400-500 per l 00,000 (must have both parts)

d. (2 pts) What was the percent increase in the death rate at that time?

% increase= ( i 000-500)/500 = l 00%

******* It has been suggested that the Spanish Flu originated in France rather than in China, specifically in the British army base at Etaples in 1916-1 9 1 7. The following is evidence for this suggestion:

• Soldiers were housed in tents and temporary 1•:.')oden barracks.

•The average population of the camp on any one-day was 100,000.

• The mortality of this outbreak was 25%- 50%.

• Some of the symptoms recorded were elevated breathing, elevated pulse, and heliotropic cyanos1s.

• The soldiers had close contact with chickens, turkeys, and swine.

Point total this page ________ _ 11

• There is evidence that the epidemic spread toward China in late 1917.

• There were no Chinese at Etaples until 191 8. The only foreign nationals from Asia were Indians.

• Near simultaneous outbreaks of the flu occurred in both the United States and Europe.

2 a. (2 pts) From the above list, give one piece of evidence that could be used to distinguish this outbreak as the Spanish Flu rather than another lower respiratory disease.

• The mortality of this outbreak was 25%-50%.

• Some of the symptoms recorded were elevated breathing, elevated pulse, and heliotropic cyanosis.

b. (2 pts) Give one precautionary measure that should be taken to prevent further tlu outbreaks in a camp such as the one at Etaples.

Reduce crowding Improve housing Break up camps

3. (2 pts) The original form of the flu virus, although giving rise to many genetic variants since 1918, reappeared in (almost) its original form in 1977. However, the vast majority of persons infected in this outbreak were in their twenties or younger. Give one explanation for the age distribution of cases in the 1977 outbreak ..

This particular strain of flu virus has a predilection for young adults. Older people had been previously exposed and were immune. Young adults were more likely to be exposed than older persons.

Figure 2. Average life expectancy by year, 1900-1960

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Figure 3. Case-fatality rate per 10,000 by age group during the Spanish flu pandemic.

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Figure 2 represents the average life expectancy between 1900 and 1960 while Figure 2 represents the age-specific case fatality rate of those with the 1918 flu.

4. a. (2 pts) What might account for the dip in life expectancy seen in Figure 2?

The Spanish flu outbreak

b. (6 pts) Based on Figure 3, what were the approximate case-fatality rates for each of the following age classes: <l yr. , 25- 34 yrs ., >85 yrs.

<1 year _2200 ___ _

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>85 years 2200 ---

c. ( 4 pts) How do the mortality patterns of the 1918 flu outbreak and the 1977 outbreak differ from those of more recent flu outbreaks?

The case-fatality rates in recent outbreaks are generally highest in the very young and very old and lowest in the middle age groups. In the 1918 outbreak, young people tended to have the highest case fatality rates. ( 1 pt for correct description of pattern for each outbreak)

5. (4 pts) Explain the types of differences in virulence (ability to kill its host) of the Spanish Flu strains you might expect between areas with large numbers of susceptible hosts and areas with much smaller numbers of susceptible hosts.

Strains from areas with large numbers of susceptible hosts may be more virulent than areas with small numbers of susceptible hosts because they would be more likely to be passed before the host died.

Point total this page ____ _ _ _ _ 13

******* Host populations can be divided into three subclasses based on the potential for infection. These are: the susceptible portion that can become infected, the already infected portion of the population, and the recovered portion. Figure 4 is a graph of the number of individuals in three portions of a host population (Y ) as an outbreak moves over time (X). Figure 4. Numbers of susceptib le, infected and recovered individuals in a population during the

course of an uutbreak

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6. (3 pts) Label each curve as susceptible, infected, or recovered. Susceptible is bottom, Infected is middle Recovered is top

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Figure 5: Schematic of Influenza A virus

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7. (6 pts) The various parts of the influenza A virus are shown in Figure 5. Draw an arrow labeled "A" to or otherwise indicate the portion of this virus that makes contact with susceptible . cells. Draw an arrow labeled "B" to or otherwise indicate the part of the virus that actually enters the cell. Draw an arrow labeled "C" to or otherwise indicate the portion of this

Point total this page ______ _ 14

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