Disease Detectives

Clinical Approach to Public Health

Primary role in diagnosis and treatment in individuals

Public Health Approach

Primary role is in control and prevention of disease in populations or groups of individuals

Ex. Diagnosing cases associated with outbreaks

1662

John Grant published landmark analysis of mortality data

1740s

Jame’s Lind designed first experiment to use a concurrently treated control group while studying scurvy’s limeys

1790s

Edward Jenner developed smallpox vaccine using clinical trials using cowpox

1800s

William Farr built upon Graunt’s work by systematically collecting and analyzing Britains mortality stats. He became the father of vital stats and surveillance

1849-54

John Snow: “Father of field epidemiology” formed and tested hypothesis on the origin of cholera in London.

One of the 1st analytic epidemiology

1843-1910

Robert Koch formalized standards (postulates) to identify organisms with infectious disease

1910s

FLU Pandemic

1920

Joseph Goldberger published a descriptive field study showing the dietary origin of pellagra.

1940s

Fluoride supplements added to public water supplies in randomized community trials

1949

Initiation of the Framingham/ study of factors for cardiovascular disease

1950

Epidemiological studies link cigarette smoking to lung cancer

1954

Field trials of the Salk polio vaccine (Largest Formal Human Experiment)

1959

Mantel and Haenszel develop statistical procedure of case studies

1960

MacMahon published first epidemiological text with focus on study design

1964

US Surgeon report on smoking and health

1970s

Worldwide Eradication of Smallpox

1980

HIV Epidemic, chronic disease, injury

1990s

Edward Sydenstricker became a pioneer in public health station

2000s

Genetic and molecular epidemiology

2001

9/11

2002

Bioterrorism: Smallpox threat with vaccinations

2003

SARS quarantines

Epidemiology

The disease detectives who work to solve public health issues

• Study of distribution and determinant of health-related states on events in specified populations, and application to control the health problem.

Purpose of Epidemiology in Public Health Practice

• Determines agent, host, environmental factors that affect health

• determines relative importance of causes o f illness, disability and death

• Types of disease agents-Biologic, physical, chemical

Steps In solving health problems

1. Collect data—Surveillance, determine Time/Place/Person Triad

2. Assessment—Inference

3. Hypothesis testing—determine how and why

4. 4. Action—Intervention

Endemic

Disease or condition present among a population at all times

Outbreak

(Localized epidemic) -more cases of a particular disease than expected in a given area or among a specialized group of people over a time period

Epidemic

Large numbers of people over a wide geographic area affected

Pandemic

An epidemic occurring over a wide area (several countries) and affecting a large portion

Cluster

An aggregation of cases over a particular period especially cancer and birth defects closely grouped in time and space regardless

Sporadic

A disease that occurs infrequently and irregularly

Risk

The probability that an individual will be affected by or die from an illness or injury within a stated time or age span

Rate

Number of cases occurring during a specific period; always dependent on the size of a population during that period

Ex: Rate(%) = (number of cases)/(population at risk) x 100

Ratio

Value obtained by dividing one quantity by another—often compares two rates

Proportion

The comparison of a part to the whole as the number of cases divided by total population—NO time dimension

Natural History of Disease Timeline

Agent

A microbial organism with the ability to cause disease

Ex. Bacteria/Fungi/Parasites

Reservoir

A place where agents can thrive and reproduce

Ex: People/Water/Food

A portal of exit

A place for an agent to leave the reservoir

Ex: Blood/secretions/excretions/skin

Mode of transmission

Method of transfer by which the organism moves or is carried from one place to another

Ex: Physical contact/ Droplets/ Airborne

Portal of entry

An opening allowing the microorganism to enter the host

Ex: Mucous Membrane/ Respiratory and Digestive systems/ Broken skin

Susceptible host

A person who can’t resist a microorganisms invading the body, resulting and multiplying in an infection

Ex: Immune Deficiency/ Diabetes/Burns/Surgery/Age

Vector

An animate intermediary in the indirect transmission now an agent that carries the agent from a reservoir to a susceptible host

Ex: Organism transmit

Fomite

A physical object that serves to transmit an infectious agent from person to person

Ex: A comb with lice, the fomite is the comb

Zoonosis

An infectious disease transmissible from animals to humans

Ex: Microbes with bacteria, viruses, fungi, Protozoa

Infectious dose

Amount of pathogen required to cause an infection

(Varies according to pathogenic agent and consumer’s age and health)

period of commmunicability

period when you are infectious and spread germs

Contamination

Infectious agent in the host, but hasn’t invaded tissues

Infection

Agent begins the invasion of host tissue (localized or systematic

Disease

When the cumulative effects of the infection cause damage in the tissue

Infecting

Proportion of exposed persons who become infected

Pathogeniatry

Proportion of infected persons who develop clinical disease

Virulence

Clinical disease who become severely ill and die

Incidence

rate of occurrence of an event; number of new cases occurring over a specific period of time

Prevalence

Number of cases of disease occurring within a population at our given point in time

Goals of Surveillance

Provide info that can be used for health action to guide public health policies and programs

Purposes of Surveillance

Assess public health status, define public health priorities, Evaluate programs, stimulate research

Surveillance Process Step 1

Data collection:

• Reported disease or syndromes/Electronic health records (e.g. hospital discharge data)

• Vital Records (birth or death certificate)/ Registries (cancer)/ Survey (National Health and Nutritional Examination survey NHANES)

Surveillance Process Step 2

Data Analysis

By place: Usual method to examine reports either by where case was reported or illnesses occurred

By location: Allows prevention resources to be directed to where exposure occurred

Surveillance Process Step 3

Data Interpretation

• Closely coupled with analysis/ identifying person, place, time to identify health event

Surveillance Process Step 4

Data Dissemination

• Distributed info to those who need to know

• Methods of Distribution: Health newsletters, surveillance reports, journals, social media

• Target audiences: public health practitioners, general public, the clinicians, policy makers, community organizations

Surveillance Process Step 5

Link to Action

• Without action, data serve no real purpose

Passive Surveillance

• More incomplete and limited variability of quality

• Ex: Physician sees patient, diagnoses measles, then inititates case report by contacting local health department and providing details for case.

Active Surveillance

• health agencies contact healthcare providers seeking reports

• More complete reporting of conditions

• Ex: health physician receives case for measles, this is triggered. They search for other cases, call the doctors office….

Sentinel Surveillance

• Can be disease event or population (Active or Passive)

• Reporting of events by health professionals selected to represent a are (Monitoring trends through high quality data)

• Ex: Network of hospitals use high-quality data on various diseases and their causative organisms

Syndromic Surveillance

• Focuses on one or more symptoms rather than physician diagnosed or laboratory

• Analysis of medical data to detect or anticipate disease outbreaks

• Ex: Outbreak affects the population as some call in sick. This system triggers monitor data with absent longs, emergency call systems, etc. (detects visual patterns)

• If spike occurs, disease epidemiologists and public health professional are alerted that there is an issue.

Experimental Studies

• Clinical trails for Individuals/Community Trials for communities

Observational Studies

Contains cohort, case control, cross-sectional and ecological studies

Cohort Study

Epidemiologist records whether each study patient is affected or not.

• Tracks the patient to see if they develop the disease of interest

Case Control Study

Investigators start enrolling a group of people with disease (case patients) and a group without the disease (control) to compare exposure between the groups.

Cross-Sectional Study

A sample of persons from a population and their exposures and health outcomes measured to assess presence(prevalence) of the health outcomes at that point of time without regard to duration.

Ecological Study

A study in which at least one variable, exposure or outcome is measured at the group.

Ex: Group level measures: Incidence rate of concern in a certain population, mean level of blood pressure of patients seen at a clinic

Outbreak Investigation Step 1

Prepare for field work

• Research supplies and equipment, disease or situation

• Administrative arrangements

• Local contacts—follow protocol and contract

Outbreak Investigation Step 2

Establish the Existence of an Outbreak

• Consider severity, potential for spread, public concern and availability of resources

• Expected number of cases for area- use records as health depts. hospital records, death records, physician records, doctor survey

• Other facts such as population changes

Outbreak Investigation Step 3

Verify the Diagnosis

• Proper diagnosis—verify the procedures used to diagnose the problem

• Commonality: Interview several persons who became ill to gain insight concerning possible cause source and spread of disease.

• Screen ill people and collect clinical and environmental samples.

Outbreak Investigation Step 4

Construct a working case definition

• Clinical info, characteristic or the affected people

• Location or place as specific as possible

Case Defintion (Under Outbreak Investigation)

Establish with the 4 components or standard criteria for determine who has the disease or condition.

Line Listing (Under Outbreak Investigation)

• Identify info—ID or case with initials

• Clinical info—diagnosis, symptoms, lab results, hospital—death

• Descriptive: Time—date and time of onset + date of report

• Descriptive: Place-street city or country + specific site

• Descriptive: Person: Age, sex, occupation

• Risk factors and causes—specific to situation and outbreak setting

Outbreak Investigation Step 5

Find cases systematically and record info

• Identifying info: Name, address

• Demographic info: Age, sex, race, occupation, etc.

• Clinical info: Signs and symptoms allow investigators to verify that the case definition has been meet.

• Risk Factor Info: Must be tailored to specific disease in question

• Reporter info: Case report must include reporter or sources so investigation can seek additional info on the results.

Outbreak Investigation Step 6

Reform Descriptive Epidemiology: Time Place Person

Time: Epidemic curve or Epi curve

Place: Geographic extent plus spot map of cases to identify groups specific to a location or environmental factors

Person: Identify the affected population by type of person or age, sex

Epidemic Curve/Epi Line

A histogram showing the course of the disease or outbreak to identify the source of the exposure

(X-axis = units of time = ¼ to 1/5 incubation time and y-axis = number of cases)

• A single point or source will have only one peal, a plateau will show a continuous common source, several peaks will indicate a propagated outbreak spread from person.

Outbreak Investigation Step 7

Develop Hypotheses

• Agent/host/environment

• Infectious groups: Viruses, Bacteria’s, Protestants, fungi, animals

• Testable—hypothesis must be in form that is testable

• Current knowledge/background: should be based upon current knowledge and be updated or modified as new info is covered.

Chain of Transmission

Agent/Host/Environment Triad

• Agent capable of causing disease and it’s source host or persons susceptible to agent + environment allowing them to get together.

Outbreak Investigation Step 8

Evaluate Hypotheses Epidemiologically-Analytical (must have control group)

1. Must have lab verification to validate a hypothesis

Cohort Study in Step 8 Of Outbreak Investigation

Based upon exposure status whether or not they have outcome used with a small well defined population.

Ex. Restrospective: Historic cohort starts at exposure in past and moves forward to outcome prospective: Moves forward in time to outcome.

Example of Cohort Study

400 people attended a special awards dinner. Someone became ill and the population at the dinner was surveyed to determine who became ill.

Attack Rate

The rate a group experienced an outcome or illness

• = number sick/total in that group

• Look for high rate attack and low rate in unexposed

Relative Risk

Estimates the association between exposure and disease

• If equals to 1, it indicates that the incidence rates of disease is equal to incidence rates in unexposed group.

• If greater than 1, indicative positive association or increased risk

• Not expressed in negative numbers

• Exposed/Unexposed = ___

Case Control Study in Step 8 of Outbreak Investigation

Works backward from effect to illness to suspected cause. Control group is a selected group who has similar characteristics to the sick group but isn’t ill.

Odds Ratio (Used in Case-Control Study)

Calculated to evaluate the possible agents and vehicles of transmission

• Odds of exposure in ages = a/c = a/d

• Odds of exposure in controls b/d = b/c

Example of Case Control Study: What is the Odds Ratio of this Study?

5.8

Outbreak Investigation Step 9

As necessary, Reconsider, Refine and Re-evaluate Hypotheses

Outbreak Investigation Step 10

Compare and Reconcile with Laboratory and/or environmental shades—verification with environmental/laboratory studies—verification with controlled conditions.

• LAB Verification NEEDED to validate Hypothesis

Bradford Hill Criteria 1

1. Strength of the Association: the stronger the association between a risk factor and outcome, the more

likely the relationship is to be causal.

Bradford Hill Criteria 2

Consistency of Findings: Have the same findings must be observed among different populations, in different study designs and at different times?

Bradford Hill Criteria Step 3

Consistency of findings: There must be a one to one relationship between cause and outcome.

Bradford Hill Criteria Step 4

Temporal sequence of association: Exposure must precede outcome

Bradford Hill Criteria Step 5

Biological Gradient: Change in disease rates should follow from corresponding changes in exposure (dose-

response).