IHP 330 Module 6 Outbreak Investigation Paper example

Forty-Eight Hours at Camp: An Outbreak Investigation of Acute Gastroenteritis at a Composite Youth Summer Camp

[Student Name]

Southern New Hampshire University

IHP 330: Principles of Epidemiology

Module Six Outbreak Investigation

[Instructor Name]

[Date]

The organization, setting and figures below are a composite written as a model document. No real employer, client, colleague or patient is described.

Forty-Eight Hours at Camp: An Outbreak Investigation of Acute Gastroenteritis at a Composite Youth Summer Camp

The Report and Verifying the Outbreak

On a Wednesday morning in July, the director of a composite overnight summer camp called the county health department. Since the previous afternoon, more than 30 campers and several staff had vomited or had diarrhea, and the camp nurse was running out of cots. The camp hosts 210 campers aged 9 to 15 and 30 staff. Because the camp normally sees one or two sick campers a week, this number was clearly above the expected level, confirming an outbreak. The epidemiologist arrived that afternoon, collected stool specimens from eight ill campers and began interviews, following the standard sequence of outbreak investigation steps (Centers for Disease Control and Prevention [CDC], 2012).

Case Definition

For this investigation, a case meant a camper or staff member at the camp between July 7 and July 14 who developed vomiting, or diarrhea (three or more loose bowel movements in a 24-hour span), with onset from July 8 onward. The definition includes the place, the time and clear clinical criteria, and it deliberately does not require laboratory confirmation, so that all likely cases are counted early. Using this definition, interviews and the nurse's log identified 68 cases among 240 people, an overall attack rate of 28.3 percent.

The Epidemic Curve

The table shows cases by 12-hour period of symptom onset.

Table 1

Cases by Time of Symptom Onset

Reading the Curve

The curve rises steeply, peaks between midnight and noon on July 10 and falls off over the next day, a pattern consistent with a point source exposure. Counting back from the peak by the usual norovirus incubation, roughly half a day to two days, places the likely exposure around midday on July 8 or 9. The long tail after the peak, with cases continuing for three more days, suggests that the first wave was followed by person-to-person spread in cabins and shared bathrooms. The single early case on July 8 turned out to be a kitchen worker who became ill that afternoon but had helped prepare lunch that morning.

Hypothesis and Food-Specific Attack Rates

Interviews showed that the kitchen worker had made the deli sandwiches for lunch on July 8 while nauseated. The leading hypothesis was that the sandwiches were contaminated. All 240 people were asked what they ate at that lunch. The table below shows attack rates for the three items served.

Table 2

Food-Specific Attack Rates for the July 8 Lunch

Note. Risk ratio equals the attack rate among those who ate divided by the attack rate among those who did not.

Interpreting the Attack Rates

People who ate the deli sandwiches were 3.5 times as likely to become ill as those who did not, and the confidence interval excludes 1 (chi-square p < .001). Most cases, 58 of 68, had eaten sandwiches. Neither fruit salad nor lemonade was associated with illness. The 10 cases among people who did not eat sandwiches are consistent with secondary spread from ill cabinmates. Together with the ill food handler and the timing, the analysis strongly supports the hypothesis.

The Likely Agent

The clinical picture, with sudden vomiting, short incubation, illness lasting one to three days and a high attack rate, fits norovirus, the leading cause of foodborne and person-to-person outbreaks of gastroenteritis in the United States (Hall et al., 2011). Even before laboratory results, the outbreak met the classic epidemiological criteria for norovirus: vomiting in more than half of cases, a mean incubation of 24 to 48 hours, illness lasting 12 to 60 hours and no bacterial pathogen found (Kaplan et al., 1982). Norovirus was later detected in six of the eight stool specimens by the state laboratory, confirming the agent. Its very low infectious dose and resistance to many disinfectants explain both the point source and the rapid spread in cabins.

Control Measures

Control followed national norovirus guidance (Hall et al., 2011). Ill food workers were excluded from food handling until at least 48 hours after their symptoms ended. Ill campers were isolated in a separate cabin with a dedicated bathroom. Bathrooms, cabins and high-touch surfaces were cleaned with a chlorine bleach solution effective against norovirus, since alcohol-based products are less effective. Handwashing with soap and water before meals and after using the bathroom was supervised by counselors, and the start of the next camp session was delayed until 48 hours after the last new case.

Lessons for the Camp

The outbreak started with a food worker preparing food while ill. The camp should adopt a written policy requiring kitchen staff to report vomiting or diarrhea and stay off work until 48 hours after symptoms stop, with paid sick time so that staff are not tempted to work while ill. Food workers should wear gloves when handling ready-to-eat foods such as sandwiches, and handwashing stations should be added near cabins. The camp nurse should also keep a daily illness log and call the health department when more than a few campers develop the same symptoms within a day, so that the next outbreak is detected at five cases rather than thirty.

Conclusion

Using a clear case definition, an epidemic curve and food-specific attack rates, the investigation traced the outbreak to deli sandwiches prepared by an ill kitchen worker on July 8, with norovirus as the agent and a second wave spread between campers. The analysis shows how each step of outbreak investigation narrows the possibilities until the source is identified and the right controls can be applied.

References

Centers for Disease Control and Prevention. (2012). Principles of epidemiology in public health practice: An introduction to applied epidemiology and biostatistics (3rd ed.). U.S. Department of Health and Human Services.

Hall, A. J., Vinje, J., Lopman, B., Park, G. W., Yen, C., Gregoricus, N., & Parashar, U. (2011). Updated norovirus outbreak management and disease prevention guidelines. MMWR Recommendations and Reports, 60(RR-3), 1-18.

Kaplan, J. E., Feldman, R., Campbell, D. S., Lookabaugh, C., & Gary, G. W. (1982). The frequency of a Norwalk-like pattern of illness in outbreaks of acute gastroenteritis. American Journal of Public Health, 72(12), 1329-1332. https://doi.org/10.2105/AJPH.72.12.1329