How cases of gastrointestinal illness represent an outbreak

Question

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.

Table:

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

Epidemiology Case Study Questions

Question 1: Do you think these cases of gastrointestinal illness represent an outbreak in the community? Why or why not?

Question 2: How is Hepatitis A transmitted? On what sources of infection should public health officials focus?

Question 3: What existing sources of information might help determine if others in the community have Hepatitis A?

Question 4:

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

b. Were symptoms among patients consistent with Hepatitis A?

c. What was the likely course of the outbreak and did it appear to be over?

Question 5: What studies or investigations might you undertake to confirm the hypothesis that contaminated food was the source of the outbreak?

Question 6: What will be your sampling approach for the survey of potential subjects? Justify your answer.

Question 7: How would you collect information from selected households for the survey?

Question 8: 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?

Question 9: What will be your case definition in this scenario?

Question 10: Write the Null and Alternative hypothesis for this case

Question 11: From figure 2, calculate the Odd Ratio (OR) and explain what it represents

Question 12: Name some of the factors that could lead to an increase in the reported number of cases.

Question 13: Contaminated food in this scenario is what type of variable?

Question 14: Looking at figure 1, what type of graph is this?

Question 15: What role does inferential statistics play in this scenario?

Question 16: Total number of the people who ate at the restaurant is______________variable.

Question 17: Graphs such as figure 1 help researchers to visualize data, what value will descriptive statistics add that the graph may not provide?

Question 18: 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.

Question 19: Offer some population-based interventions that might be used to prevent foodborne outbreaks.

Question 20: 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.