Posted: October 27th, 2022

Hepatitis Outbreak

Below are some hints on how to complete the Hepatitis case study. Remember, case studies take time and you should plan for spending AT LEAST 3-5 hours on this assignment. If you haven’t looked at the assignment yet, please view the PowerPoint and then answer the questions on the Word document. Both of these are found under Module 2. Let me know if you have any questions. For the Hep Outbreak Case Study: Use the PP document for information as you progress through the questions on the word document. The word document also has important tables and figures (located on last few pages). ***Please remember to include an Epi Curve AND calculated attack rates in your answers.

These are requested in the Powerpoint, not in the word document with the questions. You will only calculate Attack Rates for the Total of each age group. You can’t do ARs by gender b/c the populations of males/females are not given. You should end up with 13 ARs (for each age group and the Total). Example AR% equation and answer for 5-9 age group: 4 / 1000 x 100 = 0.4% You will complete the Epi Curve using Excel. First thing you need to do is list the dates in Column A (x-axis) and the # of cases in Column B (y-axis). You do not need to do a lead or end incubation period. You can start the curve with the first date of onset and end with the last date. Make sure the lag time between each mark on the x-axis is consistent (ie, 2 days, 4 days, 7 days), but don’t go above 7 day intervals. The x-axis labels should be even date increments (ex, 4/2, 4/9, 4/16, etc). You do not need to do a histogram (as mentioned in the CDC Module). Just use a column/bar chart (which is the first choice given when you go to Insert -> Chart). The x-axis label should read “Date of Onset” and the y-axis should read “Cases.”

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If you’ve never completed a chart using Excel, please give yourself enough time. That way, you’ll have time to ask me for assistance if need be. There is an article posted in Canvas on how to create a chart, entitled “Field of Epidemiology.” Make sure to read that carefully and if you have trouble, please consult the Help menu to Excel or contact the computer lab for assistance. You can either type your answers on the Hep Outbreak Word document or you can copy and paste the questions into your own Word document.

2

>HEPATITIS A OUTBREA

K

INVESTIGATION

You are a member of the Hepatitis Unit of the Centers for Disease Control and Prevention in Atlanta, Georgia. The year is

1

9

6

8

. On May 1

5

th, a request to assist in the investigation of an outbreak of infectious Hepatitis A was extended. You learned that 55 cases of infectious hepatitis had been reported to District #2 Health Department in

No

rth Trail, Michigan.

Question # 1

Knowing that between April 1 and May

15

, 1968, there were 55 cases of Hepatitis A infection reported to the County Health Department, could you conclude that this is a problem of epidemic proportion?

Justify your response.

Question #2

A. Are 55 cases in excess of normal expectancy?

B. How did you establish whether this is greater than expected?

Question #

3

As members of the Hepatitis Unit you determined that all of the reported hepatitis victims should be interviewed as the first step of the investigation. They will be interviewed in their homes if possible. What questions will you ask? You should identify at least ten questions.

What other actions might you take at this time in the investigation while you are at the victims’ homes?

Question #

4

What information can you identify from studying daily incidence and the epidemic curve?

Question #5

Make observations about the characteristics of the outbreak in terms of time (i.e, Which decade of age had the highest attack rate? And What hypothesis relative to time and person can you make at this point in the investigation?)

Question #6

Make observations about the characteristics of the outbreak in terms of place.

What can you conclude from this information about the distribution of disease in terms of time and place?

Question

7

Why is it important to calculate attack rates by age?

Question 8

Using the information calculated about place and person, what conclusions can you draw now?

Question 9

From the information in Table 3, what hypothesis can be formed about the source of the infection?

Is this type of data alone sufficient to identify a single source?

Question 1

0

Compare the listed exposures (Table 4). Which source (location) shows the largest differential between well and ill?

Explain the high exposure rates to water in both the sick and well groups.

Question

11

What conclusions can you draw about milk possibly being the source of the contamination?

Question

12

Study Figure 2. How do these data aid in the investigation?

Question 13

Review the Case Histories (attached). Are they compatible with the bakery being the source of infection?

Question 14

What would be your next step in the investigation?

Question 15

Does your epidemic curve reveal the incubation period for hepatitis?

If so, what is it?

Does this curve still support a common source of infection?

Question

16

Knowing that infectious hepatitis virus is killed by heat, what further investigation would you undertake to confirm the source of the virus?

Question

17

Do you agree with the decision? Justify your response.

Question 18

None of the bakery employees appeared ill. Why were SGPT tests performed?

Question 19

Since the epidemic had ended, why was it necessary to administer the gamma globulin?

How would you evaluate the effectiveness of this control measure?

Grade

# in class

# ill

AR (%)

1

1

2

0

0.0

2

1

0

0.0

3

37

0

0.0

2

4

0

0.0

1

5

0

0.0

1

6

0

0.0

5

7

26

0

0.0

120

8

0

0.0

9

128

1

0.9

12

2

North Trail Public School

Saint Luke’s School

Grade

# in class

# ill

AR (%)

K

1

26

2

1.6

1

1

28

0

0.0

37

2.7

1

21

41

2.4

3

10

7

4

106

1.9

26
5

120

0.8

30

6

111

0.9

32

7

110

4.5

8 9

7.5

21

143

12

8.4

10 16

12.5

11

112

93

2.2

Table 2. Attack Rates by Grade and School in Cases of Hepatitis A – Lake County, MI

Table 3.

Exposure

History of 41 Hepatitis A Cases, Ages 10-19, Lake County, MI

1

1

12

1

8

32

1

37

3

1

5

0

Food or Water

Yes

No

Unk

nown

% Known Exposed

Restaurant A

15

25

36

.6

Restaurant B

17

23

41.5

North Trail Dairy Queen

28

68.3

Spruce City Dairy Queen

19.5

North Trail Bakery

90.2

North Trail Municipal Water

36

87.8

Table 4. Comparison of the Exposure History of 41 Cases of Hepatitis A in the 10-19 year old age group with the Exposure History of a Group of 56 Well Household Members in the 10-19 year old age group, Lake County, MI

Restaurant A

15

25

1

36.6

Restaurant B

17

23

1

41.5

28

12

1

68.3

8

32

1

19.5

North Trail Bakery

37

3

1

90.2

36

5

0

87.8

Restaurant A

3

Restaurant B

15

2

North Trail DQ

39

17

0

Spruce City DQ

6

0

North Trail Bakery

26

1

North Trail Water

4

1

Hepatitis Cases

Number

Yes

Number
No
Number
Unk

% Known

Exposure

North Trail DQ

Spruce City DQ

North Trail Water

Well Household Members

22

31

39

.3

39

26.8

69.6

50

10.7

29

46.4

51

91.1

Figure 2. Percent of Total Persons Patronizing North Trail Bakery by Hour of Sale and Age

Percent of Customers by Hour of Sale and Age

0
5
10
15
20
25
30
35
7am8am9am10am11am12noon1pm2pm3pm4pm5pm
Hour of Sale
Percentage of Customers
Less than 1010-19 years20 years and over

HEPATITIS OUTBREAK INVESTIGATION
(Case Study #1)
SEE HANDOUT

QUESTION #1

TERMS
Epidemiology. The study of patterns of occurrence of disease within a group and in factors influencing disease. The study involves time, place, and person aspects of the disease (Timmreck, 1999).
Epidemic. An excessive occurrence of a disease above what would normally be expected (Friis & Sellers, 2009).
Endemic. Usual frequency of a disease.

TERMS CONTINUED
Mortality: Death
Morbidity: Illness
Surveillance: The systematic collection of data pertaining to the occurrence of specific diseases, the analysis and interpretation of these data, and the dissemination of consolidated and processed information (Friis & Sellers, 2009)

WHY COLLECT DATA ON DISEASES?
Determine incidence of disease.
Determine prevalence of disease.
Determine temporal trends in diseases.
Seasonal Variations
Annual Variations
Identify herd immunity
Identify trends in disease morbidity and mortality locally, nationally, and globally

BACKGROUND
Lake County
Area = 576 square miles
Population = 9,680 (2,025 live in North Trail)
Predominately rural, divided between farmland and forest.
Two other cities of notable size: Spruce City (435) and Basco (308).
Summer has large tourist population

CASES
Seven cases of infectious Hepatitis A were reported to the Michigan District #2 Health Department in 1967.
Four of the cases occurred in one family.
The remaining three cases were scattered in time, and no relationship could be established between them.

QUESTION #2

EPIDEMIC INVESTIGATION
By May 10, 1968 there were 40 reported cases of Hepatitis A.
By May 25, 1968 the number had risen to 69, and
By June 1, the last two cases were reported bringing the total to 71.

STEPS OF AN OUTBREAK INVESTIGATION
Review the Steps of an Outbreak Investigation PPT in the Ch. 1 folder.

QUESTION #3

TERMS
Incidence
Number of new cases
Attack rate
a special incidence rate used when cases occur rapidly over a short period of time
Prevalence
Total number of cases
Point prevalence
Period prevalence

EPIDEMIC CURVE
The epidemic curve depicts the frequency of cases over time by plotting the number of cases by date or time of onset.

EPIDEMIC CHARACTERISTICS OF TIME
There were 71 reported cases of infectious hepatitis reported in Lake county between April 1 and June 1.
Of these, 69 had date of onset of illness between May 1 and May 30.
Develop an epidemic curve using case totals from the next slide.

DAILY INCIDENCE
April 2 1 case
April 26 1 case
May 1 4 cases
May 4 10 cases
May 6 6 cases
May 8 8 cases
May 10 10 cases
May 12 15 cases
May 16 10 cases
May 18 2 cases
May 20 1 case
May 22 1 case
May 26 1 case
May 30 1 case

Total cases = 71

COMPLETE THE TABLE
Compute the attack rates (does not include the first two cases)
Note: You can only compute AR for each age category and total; you can’t do by gender because you don’t have the population by gender for each age group.

Attack Rates by Age and Sex

Age Total Pop. Cases Male Cases Female Total
0-4 1740 0 0 0
5-9 1000 2 2 4
10-14 989 14 8 22
15-19 868 18 9 27
20-24 494 1 3 4

continued

Age Group Total Pop. Cases Male Cases Female Total
25-29 455 0 1 1
30-34 435 3 0 3
35-39 545 1 2 3
40-44 540 2 0 2
45-49 588 1 0 1
50-54 526 2 0 2
55+ 1500 0 0 0
Totals 9680 44 25 69

QUESTIONS #4 AND #5

CHARACTERISTIC OF PLACE
Lake County has 4 school districts
2 are extensions from adjacent Penton County.
North Trail Public School is in the largest district (a single building complex located near downtown North Trail, serving 1,525 pupils K-12).
70% of students use the buses.

CONTINUED
North Trails also has a Roman Catholic parochial school with 240 pupils.

SOURCE OF EPIDEMIC
K-6 children were not allowed to leave the campus for lunch.
They eat at the school cafeteria or bring a lunch from home.
North Trails’ 7-12 students may leave the campus for lunch.
Many students go downtown (1 block from school)

QUESTIONS # 6, 7 AND 8
Use Table 2 for questions # 7 and 8

CONTINUED
St. Luke’s School, however, does not allow any of its students, grades 1-8, to leave the campus for lunch.
They may eat in the school cafeteria or bring a lunch from home.
Look at Table 3 for an exposure history.

QUESTION # 9

FOOD HISTORY OF WELL INDIVIDUALS
To this point, you have concentrated on the sick individuals in the population.
The attack rates were computed for specific food sources.
To build a case, it is now necessary to examine food sources in the well population.
Examine Table 4

QUESTIONS # 10 AND 11

MILK SOURCE
All commercial milk sold in Lake County comes from dairies located outside the county.
None of the commercially produced milk in Michigan is limited to Lake County alone.

QUESTION # 11

FOOD SOURCES
Common Exposure to a food item could explain the characteristics of this common-source outbreak.
The only food items prepared and consumed locally are the foods served in the restaurants, salads sold in the delicatessens, Dairy Queen ice cream, and baked goods.
Most of these products have been eaten at some time by the majority of the local residents.

CONTINUED
Almost all the cases who lived in Lake County gave a history of eating baked goods from the North Trail Bakery.
However, it was impossible, from this information alone, to determine whether the bakery was the source of the epidemic or simply a very popular establishment in town.

QUESTION # 12

SEE CASE HISTORIES

QUESTION # 13

FURTHER REVIEW OF CASES
The occurrence of infectious hepatitis one month after direct exposure to the North Trail Bakery was illustrated by Case 1.
Cases 3 and 4 showed that only contact with baked products could be associated with infectious hepatitis, because they had no contact with the North Trail municipal water supply, with local restaurants, or other food-handling establishments.

CONTINUED
None of these four cases had any history of contact with anyone known to have infectious hepatitis or jaundice.
None had a history of infections or administration of blood products within six months prior to the onset of illness, and none had a history of recent ingestion of shellfish.

QUESTION # 14

NEXT STEP?
One of the cases in Lake County was a baker’s assistant.
The 34 year old white male visited his physician on April 6, 1968, complaining of vomiting and a cold. His wife visited the same physician two days later complaining of nausea and headaches.

CONTINUED
The patient continued to work until April 11, when the diagnosis of infectious hepatitis was made.
Co-workers at the bakery reported that the patient had dark urine for at least four days before he stopped working.
He did not return to work until April 23.

QUESTIONS # 15 AND 16

INVESTIGATION OF THE BAKERY
The North Trail Bakery has served the region for 34 years. It makes a variety of breads, pastries, donuts, cookies, pies, and cakes.
It supplies donuts and some bread to local restaurants in the North Trail area and to grocery stores in Lake County.

CONTINUED
The baker’s assistant helps in practically every process of the baked goods.
In particular, he is responsible for making and glazing donuts and for icing much of the pastry.
Observation by investigators revealed that icing was spread on the pastries by hand and items to be glazed were dipped into the glaze by hand.
Since the pastry is not cooked further after glazing or icing, these processes are likely points of contamination

CONTINUED
Both glaze and icing may be kept for several days and old batches may be used to start new ones.
Bakery products not sold in one day may be sold in the next business day as “day-old”.
Therefore, contaminated foods could be available for consumption over a period of several days.

CONTINUED
In the midst of the epidemic investigation, as it became clear that the bakery was an increasingly likely source, a blood sample was taken from each person who worked in the bakery to ascertain whether there were any cases of hepatitis present at the time in the bakery employees.

CONTINUED
An SGPT was performed on each blood sample, and in all instances the SGPT was within normal limits. Because the epidemic curve showed that the outbreak was ending at this time (June 3) and because there was no elevated SGPT level found, the bakery was permitted to remain open.

QUESTIONS #17 AND 18

CONTROL MEASURES
Serum gamma globulin was immediately offered to all residents, and 7,000 to 8,000 doses were distributed after June 3, 1968.
Question # 19

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