Epidemiology Case Study

Epidemiology Case Study

The Department of Public Health (DPH) is monitoring a situation in the town of Lewis regarding a potential infectious disease outbreak. This was initially observed when a physician from a local ED reported an increased number of patients with gastrointestinal symptoms and acute hepatic abnormalities. Approximately two weeks ago, there were reports of cases presenting to the emergency department with complaints of fever, nausea, and severe fatigue. Other complaints included reports of very dark urine, and stools were very light-colored stools over the previous 24 hours. Most patients were previously healthy and had no history of jaundice. Some patients had a low-grade fever (100.6 ° F), mild scleral icterus (the whites of their eyes were slightly yellow), an enlarged liver, but no rash.

Here is an example of lab values for one patient among those in the hospital:

Liver function test:

ALT (alanine aminotransferase): 877 IU/L

AST (aspartate aminotransferase): 650 IU/L

Alkaline phosphatase: 58 IU/L

Total bilirubin: 3.4 mg/dL (within the normal valuestext annotation indicator)

White blood count and differentials were normal.

Serology tests:

Total anti-HAV: positive

IgM anti-HAV: positive

Total anti-HBc: positive

IgM anti-hepatitis B core antigen: negative

HBs Ag: negative

Anti-HBs: positive

Anti-HCV: negative

A total of 85 people were reported sick, while 15 have been hospitalized in stable conditions. Typically, this location sees no more than 10 cases of HepA per year. Many of those with symptoms who were interviewed reported having eaten at a specific restaurant in town. However, others who were symptomatic had not eaten at that particular restaurant.

What happens during HepA infection:

The graph below helps in understanding the sequence of events during Hepatitis A infection.  After ingestion, the virus is taken up by the gastrointestinal tract and travels through the blood to the liver, where it infects liver cells and replicates inside them, causing them to burst when new virus particles are released. Cell bursting releases enzymes normally found inside the liver cells, such as ALT, AST, and alkaline phosphatase, and concentrations of these enzymes in the blood become abnormally high.

A positive test for anti-HAV IgM clinches the diagnosis of acute infection. After recovery, the IgM gradually declines, but anti-HAV IgG increases, providing immunity against another hepatitis A infection. Therefore, if someone has elevated blood levels of anti-HAV IgG, but not IgM, it indicates that they had a past infection that resolved.

Figure 1.

Typical Serologic Course of HAV Infection and Recovery

Source: https://www.cdc.gov/hepatitis-a/hcp/diagnosis-testing/

 

 

Figure 2

Number of new cases

 

 

 

 

Table 1

Comparing people who ate at the restaurant and got sick and those who did not.

	Got sick	Did not get sick	Total
Ate at the restaurant	85	215	300
Did not eat at the restaurant	25	455	480
Total	110	670	780

 

Week 6 Epidemiology Case Study Questions

 

1. Do you think these cases of gastrointestinal illness represent an outbreak in the community? Why or why not? (1 point)
2. How is Hepatitis A transmitted? On what sources of infection should public health

officials focus? (2 points)

1. What existing sources of information might help determine if others in the community

have Hepatitis A?  (2 pts)

1. a. Interpret the descriptive epidemiology of the outbreak including the epidemic curve

(Figure 1) (3 points)

1. Were symptoms among patients consistent with Hepatitis A?
2. What was the likely course of the outbreak and did it appear to be over?

1. What studies or investigations might you undertake to confirm the hypothesis that contaminated food was the source of the outbreak? (3 points)
2. What will be your sampling approach for the survey of potential subjects? Justify your answer. (2 points)
3. How would you collect information from selected households for the survey? (2 points)
4. If 20% of persons not directly exposed to the contaminated source became ill, and if the contaminated food supply was the source of the outbreak, what explanations exist for these persons becoming ill? (2 points)
5. What will be your case definition in this scenario? (2 points)
6. Write the Null and Alternative hypothesis for this case (2 points)
7. From figure 2, calculate the Odd Ratio (OR) and explain what it represents (2 points)
8. Name some of the factors that could lead to an increase in the reported number of cases. (2 points).
9. Contaminated food in this scenario is what type of variable? (1 pt)
10. Looking at figure 1, what type of graph is this? (1 pt)
11. What role does inferential statistics play in this scenario? (2 pts)
12. Total number of the people who ate at the restaurant is______________variable. (1 pt)

17. Graphs such as figure 1 help researchers to visualize data, what value will descriptive statistics add that the graph may not provide? (2 pts)

1. Explain briefly how leadership might create a work environment that promotes well-being, personal health, and self-care, and reflect how this would mitigate work -related hazards such as food poisoning outbreak. (2 pts)
2. Offer some population-based interventions that might be used to prevent foodborne outbreaks. (3 points).
3. Describe how the use of data would lead to the reduction of foodborne outbreaks with regards to quick identification of the site and source of illness. (3 pts)