Application of Epidemiology (Part 4)

Implications of Health Statistics

1. Indispensable tool in planning, implementation and evaluation of any health program;

2. Serves as indices of the health conditions obtained in a community or population group;

Implications of Health Statistics

3. Provide valuable clues as to the nature of health services or actions needed; and

4. Serves as basis for determining the success or failure of such services or actions.

Disease Causation

- Need to determine the etiology of the disease

- Answer the epidemiologic question "What factors contribute to disease causation?" , "Why does disease occur?"

- Interventions that target the causes of a public health problem have greater chances of having a positive outcome

Disease Causation

- Based on valid evidence will contribute to the success of health interventions

- development of the epidemiologic disease model

epidemiologic disease model

- represents the factors that influence disease causation

- A review of the theoretical and research literature and an understanding of the natural history disease will contribute to its development

Epidemiologic approach

assumes a causal path and posits that changing or breaking a link in that causal path can either prevent the occurrence of the disease or alters its course, so that the more serious sequelae can be avoided

Determination of Disease Causation

- epidemiologic approach

- case-control studies to investigate outbreaks

- Examination of the complex interrelationships of multiple factors in disease causation through case-control and cohort, a function of analytic epidemiology

Models of Disease Causation

- epidemiologic triad or triangle mode

- Wheel model

- Web model

Epidemiologic Triad/Triangle Model

Initially, the model was applied for the infectious diseases, so the agent referred to parasites, protozoans, bacteria, viruses and other microbes

Epidemiologic Triad/Triangle Model

Later, it was applied to noncommunicable disease, the agent was expanded to nutritive factors, chemical agents and physical agents

Epidemiologic Triad/Triangle Model

The model suggest that the agent and the susceptible human host are freely interacting freely in common (physical, biologic, socioeconomic) environment.

Epidemiologic Triad/Triangle Model

- For as long as the balance is maintained or is tilted in favor of the host (due to good nutritional status and high level of immunity), disease does not occur; and

- When the balance is tilted in favor of the agent (through increased dosage, virulence, pathogenicity of the agent), disease eventually occur.

Epidemiologic Triad/Triangle Model

Sometimes environmental elements such as climate can also tilt the balance in favor of the agent.

Wheel Model

- basically the same as that of the triad

- gives emphasis on the role of the genetic make-up of the host that is presented as the inner core

Wheel Model

- outer core of the hub includes host characteristics like: sex, age, socioeconomic status and behaviors

- rim or the outer edge represents biologic, physical and chemical environment.

Web Model

- When noncommunicable disease become increasingly important as public health problems

- deemed applicable to capture the complex interrelationships of numerous factors

Web Model

- some factors increase the risk of disease, while others protect against the disease

- interconnections of these multitude of factors is visualized as a spider's web

Web Model

Under this model, disease can be prevented by breaking the weakest strand of the causal web as identified previously through various types of epidemiologic studies

Epidemiology

- used to identify the important public health problems of the community

- To determine the magnitude and distribution of the health problem in terms of who is affected and when and where the problem usually occurs

Epidemiology

- To elucidate the natural history of the disease;

- To determine why the problem disease occurs; and

- To identify the factors that contribute to disease causation

Disease Outbreak

the occurrence of cases of disease in excess of what would normally be expected in a defined community, geographical area or season

Disease Outbreak

Even the occurrence of one case of a communicable disease is considered an outbreak provided the disease is either a previously unknown disease, has never occurred in the area where the lone case is observed or has been absent from the population for a long time

Detection of Outbreak

- surveillance system or through preceptive clinicians

- infection control nurse

- laboratory worker who reports an unusual disease or relatively large number of cases of a disease

Outbreak Investigation

- imperative to be done in order to identify then eliminate the source of infection and thus prevent the occurrence of more cases

Outbreak Investigation

- In many instances, the epidemic curve is already in it is descending limb the time the investigating team arrives in the area

- If it is the case, even it the outbreak is already waning, it is still advisable to go ahead with the investigation so that strategies for preventing similar outbreaks in the future can be formulated

Outbreak Investigation

provide the opportunity to assess the preventive strategies that are used

Importance of Outbreak Investigation

- Control and prevention measures

- Severity and risk to others

- Research opportunities

- Public, political or legal concerns

- Program consideration

- Training

Sources of Outbreak Investigation

- Surveillance data

- Medical practitioner

- Affected persons/groups

- Concerned citizen

- Media

Conducting Epidemiologic Investigations

- Review of Surveillance Data

- Observation of Single Events or Clusters

- Reports from patients or members of the Community

- Factors affecting Disease Outbreak Investigation

Conducting Epidemiologic Investigations

- Factors related to the disease or health problem

- Factors related to the Health Department

- Factors related to External Concerns

Demographic Data

- Age, gender, race/ ethnicity, socio-economic status, education level

- Source: Vital Statistics date (national, regional, local); census

Groups at high risk

- Health status, and health indicators of various subpopulations in the community (ex. children, elders, those with disabilities)

- Source: Health statistics (morbidity, mortality, natality); disease

Services available/providers available

- Official (public) health departments, healthcare providers for low-income individuals and families, community service agencies and organizations (ex. Red Cross, ERUF)

- Sources: City directories, phone books, local or regional social workers, list of low-income providers local CH nurse (ex. School nurse)

Outline of Plan for Epidemiologic Investigation

1. Establish fact of presence of epidemic

2. Establish time and space relationship of the disease

3. Relations to characteristics of the group of community

4. Correlation of all data obtained

Establish fact of presence of epidemic

- Verify diagnosis = do clinical and laboratory studies to confirm the data

- Reporting

- Is there an unusual prevalence of the disease?

unusual prevalence of the disease

- Past experience of a given community

- Relation to the nature of the disease

- Which cases may be considered epidemic and which are endemic?

Establish time and space relationship of the disease

Relation of cases by days of onset to onset of the first known cases - maybe done by days, week or months

Relations to characteristics of the group of community

- Relation of cases to age, group, sex, color, occupation, school attendance, past immunization, etc.

- Relation of sanitary facilities, especially water supply, sewerage disposal, general sanitation of homes, relation to animal or insect vectors.

Relations to characteristics of the group of community

- Relation to milk and food supply.

- Relation of cases and known carriers if any.

Correlation of all data obtained

- Summarize the data clearly with the aid of such tables and charts which are necessary to give a clear picture of the situation.

- Build up the case for the final conclusion carefully utilizing all the evidences available.

Correlation of all data obtained

- Establish the source of the epidemic and the manner of the spread, if possible.

- Make suggestion as to the control, if disease is still present in community and as to prevention of future outbreaks.

Steps in Outbreak Investigation

Step 1: Prepare for field work

Step 2: Establish the existence of an outbreak

Step 3: Verify the diagnosis

Steps in Outbreak Investigation

Step 4: Construct a Working Case Definition or Define and Identify Cases

Step 5: Find Cases Systematically and Record Information

Step 6: Perform descriptive epidemiology

Steps in Outbreak Investigation

Step 7: Develop hypotheses

Step 8: Evaluate hypotheses epidemiologically

Step 9: As necessary: Reconsider, refine, and re-evaluate hypotheses

Steps in Outbreak Investigation

Step 10: Compare and reconcile with laboratory and/or environmental studies

Step 11: Implement control and prevention measures

Step 12: Initiate or maintain Surveillance

Step 13: Communicate findings

Preparation for field work

two broad categories:

a. scientific and investigative issues

b. management and operational issues

scientific and investigative issues

investigation; scientific knowledge; supplies and equipment

management and operational issues

- administrative procedures ex. Travel documents, allowances

- consultation ex. Know expected role; local contact person

outbreak/epidemic

- the occurrence of more cases of disease than expected in a given area or among a specific group of people over a particular period of time

- cases are presumed to have a common cause or to be related to one another in some way (Ex. village, town, or closed institution.)

cluster

an aggregation of cases in a given area over a particular period without regard to whether the number of cases is more than expected

cluster

Ex. the diagnosis in one neighborhood of four adults with cancer may be disturbing to residents but may well be within the expected level of cancer occurrence, depending on the size of the population, the types of cancer, and the prevalence of risk factors among the residents.

Establish the existence of an outbreak

Compare the current number of cases with the number of cases from comparable period during the previous years.

- surveillance records

- hospital records, registries, mortality statistics

- data from neighboring areas

- community survey