MPH 530 Week 5 Outbreak Investigation Case Study Example

Nine Cases in Three Weeks: A Step-by-Step Investigation of Hepatitis A Spreading Through a Downtown Shelter and Nearby Encampments

[Student Name]

University of Phoenix

MPH/530: Epidemiology Concepts and Public Health Diseases

Week 5 Assignment

[Instructor Name]

[Date]

The county, the outbreak, its cases and the response are composites written for a model paper; research findings come from the sources cited.

On a Monday in March, an emergency physician at the county's main hospital called the health department's communicable disease nurse. In the past week, she had seen three adults with jaundice and laboratory-confirmed acute hepatitis A. All three were staying at the same downtown shelter, and two used methamphetamine. The county usually saw two or three hepatitis A cases a year. This paper follows the department's investigation step by step.

Why Investigate

Outbreak investigations aim to stop transmission, but they also build knowledge about how diseases spread, test prevention strategies and strengthen partnerships between clinicians and public health (Reingold, 1998).

Step One: Confirm an Outbreak

The first question is whether cases exceed the expected number. Three cases in one week, all linked to one shelter, far exceeded the county's baseline of two or three cases a year. The nurse confirmed an outbreak the same day.

Step Two: Verify the Diagnoses

The department confirmed that each case had elevated liver enzymes and a positive antibody test for recent hepatitis A infection, and requested stored specimens for genetic sequencing by the state laboratory to see whether the cases were linked.

Step Three: Case Definition

The team wrote a case definition: a person with acute illness with jaundice or elevated liver enzymes and a positive hepatitis A antibody test for recent infection, living or staying in the county, with illness onset on or after February 15. Confirmed cases had laboratory evidence; probable cases had clinical illness and a link to a confirmed case.

Step Four: Find Cases

The team searched actively: alerts to emergency departments and clinics, review of recent laboratory reports, visits to shelters and the syringe services program with symptom screening and questions to each case about contacts. Over three weeks, they identified nine cases, seven confirmed and two probable.

Interviewing Cases

Nurses interviewed each case using a standard questionnaire covering symptoms, where they had slept and eaten, contact with other ill people, drug use and sharing of equipment and access to toilets and showers. Interviews were done where cases were most comfortable, often at the syringe services program, with a peer present. Honest answers about drug use depended on assurance that information would not be shared with police.

Step Five: Describe by Time

The epidemic curve plotted cases by onset week. It showed cases spread over five weeks, with one or two new cases each week rather than a sharp peak. A single contaminated meal would produce a tight cluster within one incubation period; this pattern suggested ongoing person-to-person transmission.

Step Five: Describe by Place and Person

Six cases had stayed at the downtown shelter, two slept outdoors nearby and one lived with a case. Seven were men, ages 24 to 58. Six reported methamphetamine use and two reported injecting drugs. Four were hospitalized; none died.

Attack Rates

Among about 140 people who stayed at the shelter during the period, six became cases, an attack rate of about 4%. Among the shelter's staff, none did, consistent with better sanitation access and vaccination among staff.

Step Six: Hypotheses

The pattern fit what had been seen elsewhere. In 2017, CDC received 1,521 reports of acute hepatitis A from California, Kentucky, Michigan and Utah, mostly among people reporting drug use or homelessness, and investigations found direct person-to-person transmission rather than contaminated commercial food (Foster et al., 2018). Hepatitis A had moved from restaurant outbreaks to spread among people with no reliable place to wash their hands. The team hypothesized person-to-person spread through shared living spaces, limited sanitation and shared drug equipment.

Testing the Hypothesis

Formal analytic studies were not essential for control, but the team compared cases with shelter residents who did not become ill. Cases were more likely to share sleeping areas and to use drugs, supporting the person-to-person hypothesis. State laboratory sequencing showed the same genetic strain in all confirmed cases.

Step Seven: Control Measures

Control began before the investigation was complete. The department offered hepatitis A vaccine at the shelter, the syringe services program and encampments, added hand-washing stations and portable toilets near encampments and worked with the shelter on cleaning and on separating ill residents.

Evidence for Vaccination After Exposure

Vaccine can protect people already exposed. In a randomized trial of contacts of hepatitis A cases, symptomatic infection occurred in 4.4% of those given vaccine and 3.3% of those given immune globulin, with the two approaches performing similarly (Victor et al., 2007). Vaccine was easier to deliver in shelters and gave lasting protection.

Reaching People

Outreach workers and peers from the syringe services program went with nurses, which built trust. In three weeks, the team vaccinated 412 people.

Step Eight: Communication

The department informed clinicians with a health alert, briefed shelter operators and city officials and published a public notice explaining the outbreak and vaccine clinics without identifying anyone. Staff avoided language that blamed people experiencing homelessness.

Declaring the Outbreak Over

The department set a clear rule: the outbreak would be declared over after two full incubation periods with no new cases linked to the cluster. Setting the rule in advance prevented both premature relief and indefinite emergency status, and it gave shelter operators a date to plan around.

Working With Partners

The shelter, syringe services program, hospitals, city officials and the state laboratory each played a role. A daily fifteen-minute call during the first two weeks kept partners aligned on new cases, vaccination numbers and problems, such as a shortage of vaccine at one site that was resolved within a day.

Continued Surveillance

The team continued enhanced surveillance for two incubation periods, about 100 days, after the last case. One additional case appeared in week six; none after.

Challenges

The investigation faced obstacles. Some cases had no phone or address, and two left the county during their illness. Shelter residents moved between shelters and outdoor sites, making exposure hard to pin down. Some people feared that public attention would lead to encampment sweeps, which could scatter people and spread the virus further. The department asked city officials to pause sweeps during the outbreak, and they agreed.

Costs of the Response

The response used about 600 staff hours over six weeks, plus vaccine and sanitation supplies. Hospital costs for the four hospitalized cases alone exceeded the cost of the vaccination campaign, reinforcing the value of prevention in shelters.

Lessons

The investigation showed that people experiencing homelessness and using drugs are at risk for outbreaks that spread person to person, and that vaccination, sanitation and trusted outreach can stop them. The department added routine hepatitis A vaccination to its shelter and syringe services work.

Conclusion

Nine cases in three weeks triggered an investigation that followed the classic steps: confirm, verify, define, find, describe, hypothesize, control and communicate. The pattern matched a national shift in hepatitis A toward person-to-person spread among people with unstable housing, and trial evidence supported vaccination after exposure. Acting early, with trusted partners, ended the outbreak.

References

Foster, M., Ramachandran, S., Myatt, K., Donovan, D., Bohm, S., Fiedler, J., Barbeau, B., Collins, J., Thoroughman, D., McDonald, E., Ballard, J., Eason, J., & Jorgensen, C. (2018). Hepatitis A virus outbreaks associated with drug use and homelessness: California, Kentucky, Michigan, and Utah, 2017. MMWR. Morbidity and Mortality Weekly Report, 67(43), 1208-1210. https://doi.org/10.15585/mmwr.mm6743a3

Reingold, A. L. (1998). Outbreak investigations: A perspective. Emerging Infectious Diseases, 4(1), 21-27. https://doi.org/10.3201/eid0401.980104

Victor, J. C., Monto, A. S., Surdina, T. Y., Suleimenova, S. Z., Vaughan, G., Nainan, O. V., Favorov, M. O., Margolis, H. S., & Bell, B. P. (2007). Hepatitis A vaccine versus immune globulin for postexposure prophylaxis. New England Journal of Medicine, 357(17), 1685-1694. https://doi.org/10.1056/NEJMoa070546