writing
Prasannata
HepOutbreakPowerPoint11.pptHEPATITIS 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
