| Course | NS305 Food Safety |
|---|---|
| Unit | Unit 7 |
| Paper type | Outbreak investigation |
| Length | About 1,160 words, 7 pages double-spaced |
| Format | APA 7 student paper |
| School | Purdue University Global |
| Program | BS in Nutrition Science |
| Updated | October 2026 |
Free sample paper for NS305 Unit 7
Forty-One Absences After a Tuesday Lunch: A Unit 7 Outbreak Investigation Tracing Clostridium perfringens to a Pan of Braised Brisket
[Student Name]
Purdue University Global
NS305: Food Safety
Unit 7 Outbreak Investigation
[Instructor Name]
[Date]
The parts plant, its cafeteria, workers, counts and laboratory results are composite; the outbreak epidemiology, national estimates, cooling study and Food Code limits cited are real.
Notification
At 7:15 a.m. on Wednesday, the plant's occupational health nurse called the county health department. Eleven workers on the first shift had called in sick, all with diarrhea and cramps, and the nurse had heard of more on the second shift. Every one of them had eaten in the plant cafeteria on Tuesday. The department opened an investigation that morning.
Case Definition and Case Finding
A case was defined as diarrhea or abdominal cramps beginning within 24 hours of Tuesday's lunch in a plant employee who bought food in the cafeteria that day. Investigators used the cafeteria's register records to identify 147 employees who bought lunch, and reached 112 of them by phone or in person by Thursday. Of these, 41 met the case definition and 71 did not.
Onset and Symptoms Before Any Food
Onsets clustered tightly. The first case began at 6:30 p.m. Tuesday, six hours after lunch, and the last at 6:00 a.m. Wednesday, eighteen hours after lunch, with a median of about ten hours. Diarrhea was reported by 39 cases and cramps by 40; only 4 reported vomiting and 3 reported fever. Most recovered within a day.
That pattern narrows the field before any food is named. A six-to-eighteen-hour incubation with cramps and diarrhea, little vomiting and no fever fits Clostridium perfringens. It argues against Staphylococcus aureus and Bacillus cereus emetic toxin, which act within a few hours and cause vomiting, and against norovirus, which typically brings vomiting and spreads from person to person over several days. Clostridium perfringens is among the most common causes of foodborne illness in the United States, with nearly a million domestically acquired illnesses a year estimated (Scallan et al., 2011).
Cases Compared With Well Coworkers
Each of the 112 employees was asked what they ate from Tuesday's menu: braised brisket with gravy, mashed potatoes, green beans, tossed salad, cornbread and a vegetarian pasta.
Brisket stood apart. It was eaten by 39 of 41 cases and by 22 of 71 well coworkers. Among those who ate brisket, 39 of 61 became ill, an attack rate of 64 percent; among those who did not, 2 of 51 became ill, 4 percent. The odds ratio was about 43. Mashed potatoes were eaten by 30 of 41 cases and 48 of 71 well coworkers, a difference too small to matter. No other food came close. The gravy was ladled over the brisket and was not eaten separately, so its role cannot be separated from the meat's, and the report treats them as one dish.
The two cases who did not report eating brisket may have misremembered or tasted it from a coworker's plate. They do not weaken the finding, which rests on the size of the difference.
The Brisket's Path Through the Kitchen
Investigators interviewed the cafeteria's three cooks and reviewed its logs. The path ran as follows.
1. Monday, 1:00 p.m. Two whole briskets, about 15 pounds each, were braised for four hours.
2. Monday, 5:30 p.m. The briskets were placed whole, with their liquid, in one six-inch-deep hotel pan, covered tightly with foil and put in the walk-in to cool overnight.
3. Tuesday, 9:00 a.m. The cook sliced the brisket, still cool, into a steam table pan with gravy.
4. Tuesday, 10:30 a.m. The pan went into the steam table on its warm setting. At 11:00 a.m. the cook probed it at 148°F and recorded that reading.
5. Tuesday, from 11:30 a.m. until about 1:00 p.m. The brisket was served from the steam table. No further temperatures were recorded.
The brisket failed twice: it cooled too slowly in a deep, covered pan, giving perfringens spores the hours they need to germinate and multiply, and it was reheated in a steam table that never brought it to 165°F, so the bacteria were still alive when it was served.
Both failures are typical. In a national study of outbreak data, beef was the food most often implicated in perfringens outbreaks with a single food commodity identified, and restaurants and caterers were the commonest settings (Grass et al., 2013). In a study of 420 restaurants, many cooled food in deep containers or covered them during cooling, and about four in ten managers said they never tracked how long food took to cool or how warm it was along the way (Brown et al., 2012).
A Cooling Test After the Fact
Because no cooling record existed, investigators asked the cafeteria to repeat the process the following week with one brisket, in the same pan, the same walk-in and the same foil, with a probe logger in the thickest part. The brisket took 7 hours to fall from 135°F to 70°F and did not reach 41°F until 15 hours after cooling began. Under the Food Code, cooked food must drop from 135°F to 70°F in no more than 2 hours and reach 41°F no later than 6 hours after cooling starts (U.S. Food and Drug Administration [FDA], 2022). The test brisket missed both limits by wide margins.
Laboratory Results in Their Place
Stool specimens from six cases were tested; five were positive for Clostridium perfringens enterotoxin. A sample of leftover brisket from the walk-in yielded more than 100,000 Clostridium perfringens per gram. These results confirm the organism and the vehicle, but they arrived on Friday, after the epidemiologic analysis had already pointed to the brisket. The laboratory supported the investigation; it did not lead it.
Controls Tied to the Failed Steps
Each recommendation is tied to the step it fixes.
1. Cooling. Slice or portion large cuts before cooling, cool in pans no more than two inches deep, leave them uncovered until cold, and log time and temperature at the start, at 2 hours and at 6 hours.
2. Reheating. Reheat cooked food intended for hot holding to 165°F within 2 hours, on the range or in an oven, not in the steam table (FDA, 2022).
3. Hot holding. Hold at 135°F or above, and log a temperature every two hours during service.
4. Training. Teach the cooks why spores survive cooking and why the cooling clock matters, not only the numbers.
Limits of the Investigation
Thirty-five lunch buyers were never reached. Food histories were taken one to two days after the meal and may contain errors. The repeated cooling test used one brisket, not two, and the walk-in may have been more or less full than on the Monday in question. The conclusion is still strong because the onset pattern, the food history, the kitchen history and the laboratory all point the same way.
References
Brown, L. G., Ripley, D., Blade, H., Reimann, D., Everstine, K., Nicholas, D., Egan, J., Koktavy, N., & Quilliam, D. N. (2012). Restaurant food cooling practices. Journal of Food Protection, 75(12), 2172-2178. https://doi.org/10.4315/0362-028X.JFP-12-256
Grass, J. E., Gould, L. H., & Mahon, B. E. (2013). Epidemiology of foodborne disease outbreaks caused by Clostridium perfringens, United States, 1998-2010. Foodborne Pathogens and Disease, 10(2), 131-136. https://doi.org/10.1089/fpd.2012.1316
Scallan, E., Hoekstra, R. M., Angulo, F. J., Tauxe, R. V., Widdowson, M.-A., Roy, S. L., Jones, J. L., & Griffin, P. M. (2011). Foodborne illness acquired in the United States: Major pathogens. Emerging Infectious Diseases, 17(1), 7-15. https://doi.org/10.3201/eid1701.p11101
U.S. Food and Drug Administration. (2022). Food Code 2022. U.S. Department of Health and Human Services. https://www.fda.gov/food/fda-food-code/food-code-2022
What the NS305 Unit 7 assignment asks for
The Unit 7 assignment asks students to work through a foodborne outbreak investigation, usually from a scenario with case data. Prompts generally expect a case definition, descriptive epidemiology, an analysis of foods, an environmental assessment and recommendations. Write the case definition with time, place and symptoms. Use onset times and symptoms to narrow the likely organisms before analyzing foods. Compare ill and well people who ate the same meal, using attack rates or odds ratios. Trace the implicated food through the kitchen and name the steps that failed. Place laboratory results after the epidemiology unless they arrived first. Tie each recommendation to a failed step. Expect the finished report to fill six to eight pages.
How this NS305 Unit 7 example is built
The report opens with a nurse's call after eleven workers missed a shift. The case definition and case finding reach 112 of 147 lunch buyers. Onsets between six and eighteen hours, with cramps and diarrhea but little vomiting or fever, point to Clostridium perfringens. The food analysis gives attack rates of 64 percent for brisket eaters and 4 percent for others. The kitchen path is listed step by step from Monday's braise to Tuesday's service. The highlighted sentence names the two failures. A national outbreak study and a restaurant cooling study show that both failures are common. A repeat cooling test shows the brisket missed both Food Code cooling limits. Laboratory results follow, then four controls and a limits section.
Reading the NS305 Unit 7 grading rubric
Outbreak investigations are usually graded on epidemiologic reasoning, accurate calculations and the link between the kitchen findings and the controls. A clear case definition is expected. Using the incubation period and symptoms to narrow the organism earns credit for method. Correct attack rates or odds ratios are often checked closely. The environmental assessment is weighted heavily in a food safety course. Recommendations should each address a specific failure. APA citations and a clear structure are scored too. Reports that name the food without explaining how it became contaminated or allowed growth usually lose the most points. Discussing confounding, such as gravy served on the meat, is often credited.
NS305 Unit 7 help from the desk
Outbreak reports often name a food without showing the comparison that implicates it. Another weakness is letting laboratory results drive the story, when the epidemiology came first. Some writers skip the onset pattern and so never rule out other organisms. Calculations are sometimes wrong or unlabeled. The kitchen history is often reduced to a single sentence about improper cooling. Controls are generic and not tied to the steps that failed. Limits, such as unreached buyers, are rarely discussed. If you have the case data but are unsure how to read it, start with onset times and symptoms. Our writers can draft the report from that starting point through the kitchen findings.
Get an NS305 Unit 7 example written to your instructions
A line list, an interview summary, inspection notes, sometimes all three: outbreak cases arrive in many forms. Forward the complete NS305 Unit 7 packet with the report format and the rubric. The free first custom sample identifies the vehicle within 24-48 hours and follows the failure back to a step inside the kitchen, where much of this unit's credit usually sits. The paper above is an original model document written by our desk, not a submitted student paper and not an official Purdue University Global document.
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NS305 Unit 7 questions, answered
Why a case-control comparison instead of attack rates?
Attack rates need everyone who was exposed, ill or well. When only some buyers can be reached, comparing cases with a sample of well people who ate at the same place is the practical option, and odds ratios become the measure. Many classroom scenarios specify the design; where yours does not, state which you chose and why.
How much does the environmental assessment matter?
In a food safety course, often the most. Identifying the food answers a public health question; explaining which step allowed survival or growth answers the food safety one. The example gives the kitchen a third of the report, with the food's path, the records found and a measured cooling test, because most rubric criteria in this unit sit there.
Where can I find a free NS305 Unit 7 sample paper?
This page has a complete Unit 7 investigation tracing a cafeteria outbreak to braised brisket, with a case definition, food comparison, kitchen history and controls.
What are the typical symptoms of Clostridium perfringens food poisoning?
Diarrhea and abdominal cramps beginning about 6 to 24 hours after eating, usually without vomiting or fever, lasting less than a day. Large cuts of meat cooled too slowly are a common source.
Why does slow cooling cause Clostridium perfringens outbreaks?
Its spores survive cooking. If food cools slowly, the spores germinate and the bacteria multiply quickly, so the Food Code limits cooling to 2 hours from 135°F to 70°F and 6 hours in total to 41°F.