| Course | PHLT 8522 Epidemiological Investigations |
|---|---|
| Week | Week 2 |
| Paper type | Case definition brief |
| Length | About 580 words, 5 pages |
| Format | APA 7 student paper |
| School | Walden University |
| Program | PhD in Public Health |
| Updated | October 2026 |
Free sample paper for PHLT 8522 Week 2
Strict on the Laboratory, Generous on Place: A Three-Tier Outbreak Case Definition for Composite Histoplasmosis Cases Linked to a Riverfront District
Student Name
Walden University
PHLT 8522: Epidemiological Investigations
Instructor Name
Month Day, Year
Strict on the Laboratory, Generous on Place: A Three-Tier Outbreak Case Definition for Composite Histoplasmosis Cases Linked to a Riverfront District
Purpose
With the signal judged real, the investigation needs a case definition that decides who counts. A definition for an outbreak is not the same as a surveillance definition. It adds limits of person, place and time so that the count reflects this event, and it can be tiered so that early, sensitive counting does not contaminate later, specific analysis. The definition below builds on the national histoplasmosis surveillance definition (Centers for Disease Control and Prevention [CDC], 2017) and adds the event's own boundaries.
The Three Tiers
Table 1
Outbreak Case Definition, Composite Riverfront Histoplasmosis Investigation
| Tier | Clinical | Laboratory | Place and time | |
|---|---|---|---|
| Confirmed | Two or more of fever, cough, chest pain, shortness of breath, myalgia or headache, or abnormal chest imaging | Culture, histopathology, H band on immunodiffusion, fourfold rise in complement fixation titer or validated PCR | Lived, worked or spent at least one hour in the riverfront district, September 1-30; onset September 4 to October 31 | |
| Probable | Same | Positive antigen in urine or serum, single complement fixation titer of 1:32 or higher, or M band without a prior negative | Same | |
| Suspect | Pneumonia diagnosed by a clinician, or abnormal chest imaging | No fungal test performed | Same, and a household member or coworker is a confirmed or probable case | |
Note. District boundaries are the eight census blocks between the river and Fourth Street; dates are composite.
Why the Laboratory Criteria Stay Strict
The confirmed tier uses only the confirmatory criteria from the national definition. Antigen tests, which most clinicians order first, sit in the probable tier because they are non-confirmatory and can cross-react with blastomycosis (Hage et al., 2011). Keeping them out of the confirmed tier means the analytic study can be repeated on confirmed cases alone, a check that would fail if the top tier mixed test types. Most probable cases are expected to move up as convalescent serology returns.
Why Place Is Generous
Place is defined by any time spent in the district, not by residence. Airborne spores do not respect home addresses, and outbreaks from demolition can reach people who only passed through or worked nearby (Benedict & Mody, 2016). A residence-only definition would miss the print shop worker who lives across the river and was among the first three reports. One hour is a low threshold on purpose: at this stage, the cost of including a person who was barely exposed is smaller than the cost of never finding a true case.
Why Time Has These Limits
Onset dates run from September 4, a few days after the earliest dust-generating work could have begun, to October 31, which allows for the longest incubation periods reported in outbreaks after exposure ended in late September. Benedict and Mody (2016) found median minimum and maximum incubation periods of 7 and 15 days across reported outbreaks, so the window is wide but not open-ended.
Why a Suspect Tier Exists
Many people with outbreak-related pneumonia never receive fungal testing; they are treated for bacterial pneumonia and recover. The suspect tier holds them so case finding can return to them, offer testing and either promote or remove them. Suspect cases are counted separately and never enter the analytic comparison.
What the Definition Excludes
People with compelling evidence of another fungal infection are excluded, as are chronic histoplasmosis cases with illness that began before September. Repeat acute infections in the same person within 24 months count once.
References
Benedict, K., & Mody, R. K. (2016). Epidemiology of histoplasmosis outbreaks, United States, 1938-2013. Emerging Infectious Diseases, 22(3), 370-378. https://doi.org/10.3201/eid2203.151117
Centers for Disease Control and Prevention. (2017). Histoplasmosis 2017 case definition. National Notifiable Diseases Surveillance System. https://ndc.services.cdc.gov/case-definitions/histoplasmosis-2017/
Hage, C. A., Ribes, J. A., Wengenack, N. L., Baddour, L. M., Assi, M., McKinsey, D. S., Hammoud, K., Alapat, D., Babady, N. E., Parker, M., Fuller, D., Noor, A., Davis, T. E., Rodgers, M., Connolly, P. A., El Haddad, B., & Wheat, L. J. (2011). A multicenter evaluation of tests for diagnosis of histoplasmosis. Clinical Infectious Diseases, 53(5), 448-454. https://doi.org/10.1093/cid/cir435
What the PHLT 8522 Week 2 instructions ask for
Case definition assignments ask students to write the criteria that decide who counts in an investigation and to justify each one. Expect to specify clinical, laboratory, person, place and time elements, often in tiers such as confirmed, probable and suspect. Instructors look for an explanation of how the outbreak definition differs from a surveillance definition and why. The trade-off between sensitivity and specificity is usually central: early definitions are often broad to find cases, while analytic work relies on the strictest tier. A table is common, with one to two pages of justification. Students should cite the surveillance definition they adapt and evidence on test performance or incubation. Many prompts also ask what the definition excludes and how suspect cases will be resolved.
Inside the PHLT 8522 Week 2 example
The brief opens by distinguishing an outbreak definition from a surveillance definition. Its single table gives each tier a clinical, a laboratory and a place-and-time column, and its note defines the district by census blocks. A section on laboratory criteria explains why antigen sits in the probable tier, citing cross-reactivity data, and notes that the analytic study can be repeated on confirmed cases. A section on place defends counting any hour in the district with the example of a worker who lives across the river. A section on time ties the onset window to published incubation periods. Further sections explain the suspect tier and list exclusions, including other fungal infections and chronic disease.
PHLT 8522 Week 2 rubric: what earns full marks
Case definitions are scored on precision, justification and fitness for purpose. The sample earns precision credit by naming each laboratory criterion and each boundary in measurable terms. Justification credit comes from explaining why the laboratory side is strict and the place side generous, with a concrete case that a residence-only rule would miss. Fitness for purpose is shown by the tier structure, which supports broad case finding while protecting the analysis. Tying the time window to published incubation periods earns evidence credit. The exclusions section shows attention to false positives. Formatting, table clarity and citations take the remaining rows. Definitions that lack a time window or mix test types in the top tier usually lose most of the precision marks.
PHLT 8522 Week 2 help: mistakes that cost marks
A common error is copying the surveillance definition and stopping. Add person, place and time limits that fit your event. Decide which laboratory results are strong enough for the top tier and put the rest lower. Define place by exposure, not only by residence, when the agent travels through air or water. Base the time window on incubation evidence and the dates of possible exposure. Use a suspect tier for people who were never tested, and plan how to resolve them. State exclusions, especially conditions that cause false-positive tests. Present the tiers in a table. If your instructor supplies a different agent, the same structure works, and a first definition for it is free from us.
Get a PHLT 8522 Week 2 example written to your instructions
Name the event your section is defining cases for, and attach the Week 2 prompt and rubric. The definition sets clinical, laboratory, time and place rules, sorts people into tiers, and argues each boundary against a tighter and a looser version. The first one is free, with delivery in 24-48 hours.
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PHLT 8522 Week 2 questions, answered
Where can I find a free PHLT 8522 Week 2 sample paper?
This page holds a complete Week 2 case definition brief, with three tiers for a histoplasmosis event, a definition table and verified references.
How is an outbreak case definition different from a surveillance definition?
An outbreak definition adds limits of person, place and time for one event and is often tiered, while a surveillance definition is designed for routine national counting.
Why put antigen-positive cases in the probable tier?
Antigen detection is non-confirmatory under the national definition and can cross-react with blastomycosis, so keeping it out of the confirmed tier lets the analysis be checked on the strictest cases.
Why define place by time spent rather than residence?
Airborne spores reach people who work in or pass through an area, not only residents, so a residence-only rule would miss real cases.
What is a suspect case for?
It holds people with compatible illness and an exposure link who were never tested, so case finding can return to them, offer testing and promote or remove them.