Alcan City health officials contacted the Centers for Disease Control and Prevention (CDC). The CDC can serve as lead coordinator between public health partners to detect a foodborne outbreak, define its size and extent, and identify the source of an outbreak (CDC, 2019). Health professionals investigate foodborne outbreaks to control and prevent them from happening in the future.
For this Assignment, you will complete a case study on a foodborne outbreak. All the documents for the Assignment may be downloaded from the Week 4 Learning Resources.
Centers for Disease Control and Prevention (CDC). (2019b). Foodborne outbreaks. Retrieved from https://www.cdc.gov/foodsafety/outbreaks/index.html
To prepare for this Assignment:
Download and carefully read the following documents:
For this Assignment complete the following:
Submit your completed In the Field Foodborne Outbreak Case Study Worksheet document, including responses to all questions, your Epidemic Curve, and your explanation of what the Epidemic Curve indicates about the foodborne outbreak.
An outbreak (epidemic) of gastroenteritis occurred in Greenport, a suburban neighborhood, on the evening of April 28. A total of 95 people went to the emergency departments of the three local hospitals during that evening. No more cases were reported afterward. These patients complained of headache, fever, nausea, vomiting and diarrhea. The disease was severe enough in 25 patients to require hospitalization for rehydration. Gastroenteritis outbreaks like this are usually caused by the consumption of a contaminated meal. Meal contamination can often be caused by pathogenic viruses or bacteria. Acute outbreaks are often produced by toxins from bacteria such as Staphylococcus spp., Clostridium perfringens, Salmonella spp. and Vibrio cholerae. Norovirus strains are also common causes of acute outbreaks.
The local health department was notified of a potential food-borne outbreak of gastroenteritis in Greenport, and the epidemic team, including an epidemiologist, a microbiology technician and a nurse, visited the local hospitals to interview the attending physicians, the patients and some of their relatives. Some stool samples were obtained from patients for microbiologic identification of the causative agent. The epidemic team knew these types of outbreak usually occur in a very short time period that lasts no more than a few hours or one to two days after people ingest a contaminated meal.
Epidemic investigators gather data to define the distribution of the disease by time (onset time and epidemic curve), place (potential places where the implicated meal was served, such as cafeterias, restaurants and picnics) and person (the distribution of the disease by age, gender and food items eaten). The findings of the initial investigation included the following information.
The distribution of the disease by person (age and gender) was found as follows:
Gastroenteritis Outbreak Findings by Person, Case Distribution by Age and Gender
% Female (in age group)
% Male (in age group)
11 and older
Total by Gender
Please calculate the totals for each column and row and their corresponding percentages to try to determine if there are any important differences by age or by gender. For the column under female and male, you will be calculating the percentage of female and male cases in that age group out of the total number of cases for that age group. For example, if there were 4 female cases in the first age group and a total of 6 cases (both female/male), then the percentage of female cases in that age group is 66.67%. For the last column (total), you will divide the number of cases in each age group by the total number of cases (all age groups) and multiply by 100 to get the percentage.
This task is carried out to investigate if there are any high-risk groups and if the age and gender distribution can give some clues about the source of the outbreak. Discuss the age group and gender with the highest proportion of cases.
Construct an Epidemic Curve (use Excel; please review the document entitled, “Constructing an Epidemic Curve Using Excel” to practice). Put the times in the A column of the spreadsheet and the number of cases in the B column. Then click to insert a column (bar) chart. Insert the chart on the last page of this document.
Case distribution (by times):
8:00pm 1 11:00pm 17
8:30pm 1 11:30pm 9
9:00pm 5 12:00am 8
9:30pm 8 12:30am 7
10:00pm 12 1:00am 5
10:30pm 20 1:30am 2
Your epidemic curve shows the onset time of illness in the 95 patients involved in the outbreak. The epidemic team studied the curve and recognized that this was a typical single (point) source acute outbreak. The team also could see that the onset of symptoms in all patients occurred during a six-hour period. Given the symptoms mentioned above and the epidemic curve, the epidemic team concluded that this type of epidemic usually corresponds to intoxication or food poisoning and that the potentially implicated meal was probably served and consumed within a period of a few hours before the onset of the symptoms. Therefore, the epidemic team investigated the places where affected persons, their relatives and neighbors ate that day (April 28). The following table shows the team’s findings. Note: Often, during interviews, more ill persons will emerge (who did not seek medical attention and may/may not be part of this outbreak).
Gastroenteritis Outbreak Findings by Place
People Who Attended
Number Ill from those who attended
Attack Rate (%)
People Who Did Not Attend
Number Ill from those who did not attend
Attack Rate (%)
Lions Club luncheon
Elementary school cafeteria
Please calculate the attack rates (multiply your answer by 100 to get the AR%) by place to try to determine where the contaminated meal was served. For each place compare attack rates (AR) for those who attended with attack rates for those who did not, by using the relative risk (i.e., RR = AR in attendees/AR in nonattendees). Round all answers to the hundredths (i.e, 2.23 vs 2.2). Relative Risk is not a percentage, so only use % to denote ARs. You will calculate RRs for place and then food items. So, if one of the places above had an RR of 3.92, your interpretation of the RR would be that “those who ate at [name of place] had nearly 4 times the risk of gastroenteritis”. If any of the RRs are well below 1.0, that would mean the location or food was protective of gastroenteritis ~ meaning those who ate at a certain location or ate an item were less likely to be ill. For example, if an RR for a food was 0.32, you could state that “those who ate that food were 68% less likely to have gastroenteritis”. You find the % by subtracting the lower RR from 1.0.
Interpret your findings from the above table.
Once the implicated place was determined, the investigation centered on the food. The following table includes the food items served in that place on April 28:
Gastroenteritis Outbreak Findings by Person
Ate the Food Item
Did Not Eat the Food Item
Attack Rate (%)
Attack Rate (%)
Important note: None of the kitchen personnel were ill. The names of the kitchen personnel and their participation in the food preparation are as follows: Manuel prepared the beef burritos and the potatoes, John prepared the salad and the fruit, Sally served all dishes except the ice cream, and Jane prepared the cheeseburgers and served the ice cream. The ice cream was a commercial brand and was bought at a nearby supermarket.
Please calculate the attack rates per 100 (noted as a percentage) by food item to try to determine the one that was probably contaminated. Compare attack rates (AR) for those who ate the food item with attack rates for those who did not eat the food item, by using the relative risk (i.e., RR = AR in those who ate the food/AR in those who did not eat the food). Round your answers to the hundredths (i.e, 2.23 vs 2.2). Relative Risk is not a percentage, so only use % to denote ARs.
Interpret your findings below.
Given that the epidemic team worked fast enough and the implicated meal(s) was (were)
identified before all food leftovers were discarded, food samples from some meal leftovers were taken to the laboratory. In addition, stool samples were taken from the kitchen personnel who prepared or handled each different food item. The laboratory confirmed that Salmonella toxin was present in some of the food samples and that one of the kitchen personnel of that place had the same Salmonella species. Furthermore, the Salmonella species found in the food and the kitchen worker was the same species found in stool samples of the patients. Please discuss these findings and identify the kitchen worker possibly responsible for the outbreak.
To determine which food item(s) are responsible, is it enough to just calculate the ARs for those who ate the food items? Why or why not? (Give a thorough response)
Insert Epidemic Curve on this page.