Unit 1

Advantages of Frequency (Raw count)

- Actual number of events - Useful for determining need for services or programs

Descriptive Epi. Person Examples

- Age - Race/ ethnicity - Gender - Income - Occupation - Education - Biological (blood type) - Personality - Birth order - Marital Status

Advantages of specific rates

- Calculated for homogeneous subgroups - Comparisons of different populations - Identifies subgroups at risk

Disadvantages for using Specific Rates

- Cumbersome to compare more than two subgroups of two or more populations of interest

What are some objectives of surveillance?

- Describe distribution of health problems (health inequalities/disparities) - Monitor disease trends - evaluate effectiveness of interventions trigger investigation of etiology and control of disease transmission - Educate - Establish national priorities

Advantages of using adjusted rates

- Differences in the adjusted factor between populations removed - Permits unbiased comparison relative to adjusted factor

Cohort Study

- Exposed and non-exposed individuals followed to determine development of disease

what is infection?

- Foreign agent that multiplies within host and body reacts to presence 1. Asymptomatic (can transmit the disease, but they don't have a symptomatic response) 2. Symptomatic (both can transmit and show symptoms) 3. Latent infection (come and go, stay latent for a long period, over a period of time your body mounts a response). - Colonized/Carrier (not infected but people that harbor pathogen are capable of transmitting infection): Persistence and multiplication of agent on mucosal surface w/o apparent host reaction - Contamination: Presence of agent on surface of body or inanimate object that may serve as source of infection

Disadvantages of using Crude rates

- Influenced by population characteristics - Comparisons may be confounded by these characteristics

Disadvantages of using Frequency (Raw count)

- Influenced by size of population

Specific measures

- Measures for the population subgroups - restricts the numerator and denominator to specific subgroups (age, sex, race).

NNDS

- National Notifiable Disease Surveillance System - Council of State and territorial Epidemiologists (CSTE) meet yearly and votes to establish the national list od notifiable disease - the CSTE also vote on specific case definitions for each notifiable disease - CDC adopts the notifiable disease list and the case definitions

National disease reporting

- No law mandates national disease reporting - states have similar statues and rules. these are modified within each state - States report cases voluntarily to CDC through NETSS

Edward Jenner

- Observed milkmaids - Cow pox virus - Small pox vax

Active Surveillance

- Reports are solicited from reporting sources at established intervals or for emergent needs. -Increased sensitivity -Increased specificity -Increased collection of appropriate specimens -Increased submission to public health labs for specialized typing or ID -Limitations: resource intensive, difficult to maintain for extended periods of time. Generalities: Costly, Increased human resource requirements, data quantity and quality improved, more timely, REDUCED sustainability.

Nine measurable attributes of Surveillance systems

- Simplicity - Flexibility - Data quality - Acceptability - Sensitivity - Positive predictive value - Representativeness - Timeliness - Stability

Adjusted measures

- Summary measures for total population statistically transformed to remove the effect of differences in population composition (such as age --> important on descriptive epidemiology) - Allows fair comparisons - When you want to compare populations

Advantages of using Crude Rates

- Summary rate - easily calculated - risk of dying in the population for a given time period

What do you need to complete the indirect method of adjustment?

- Th number in each age-group for the populations to be compared. - the total number of deaths in the populations to be compared. - the age-specific death rates for the selected standard populations

What happens when you change the standardization rate?

- affects the magnitude of the rate - does not indicate changes in in disease incidence or mortality - same standard population should be used when comparing age-adjusted rates

Disadvantages of using Adjusted rates

- artificial rate - does not represent risk of dying - absolute magnitude dependent on standard population chosen

Surveillance of Disease Definition

- the continuing scrutiny of all aspects of occurrence and spread of a disease that are pertinent to effective control. - Systematic collection of: .Morbidity and Mortality .Reports of individuals cases and field investigations of epidemics and outbreak investigations .Isolation and identification of infectious agents by labs .Data on exposures and risk factors

Cholera epidemics

- water-borne, person to person (fecal-oral) - 19th century - Start of international disease control organizations

Standardized Rates

-Changes in the standard affects the magnitude rates -recalculation of disease rates based on different standards does not indicate changes in disease incidence or mortality - the same standard population should be used when comparing age-adjusted rates

Uses of epidemiology

-Identification of causes of disease -Monitoring the frequency and distribution of disease -Measuring the disease burden in populations -Evaluating the impact of intervention programs

Descriptive epidemiology Place examples

-Natural Boundaries (climate, water supply, temperature) -Political Subdivisions -Urban-Rural -International -Migrant Studies

descriptive epidemiology Time example

-Secular trends -Cyclic or seasonal changes -Short-term fluctuation -Time/place clusters

Orient data to Time, Place, and Person

-Time: •Epidemic curve: Point source vs Person-to-person, Incubation period, period of exposure •Very important if agent is unknown •Possibly predict how many more cases are likely to occur •Excellent tool for communication •Place -Disease may be associated with a location -Plot the data on a map -A distribution pattern may appear that approximates known sources and routes of potential exposure...vehicle, mode of exposure -GIS technology in an emerging tool/field in epidemiology •Person -Examine characteristics of cases •Age, gender, race, occupation, or other •If a special attribute emerges, may provide evidence of who is at risk and possible exposure •Dates: symptom onset, diagnosis, resolution of symptoms

Relative Status of Rates Interpretation guide

-When Crude is LOW and Adj is LOW: Low rate not due to age, other conditions are favorable -When Crude is LOW and Adj is HIGH: Low rate due to favorable age factor; other conditions re unfavorable -When Crude is HIGH and Adj. is LOW: High rate due to unfavorable age factor; other conditions are favorable. -When Crude is HIGH and Adj. is HIGH: High rate not due to age factor; other conditions are unfavorable.

Why can there be changes in the mortality trends?

1. Artifactual -Numerator errors due to (different classification of disease and changes in recognition - Denominator error (enumeration of the population) 2. Real -Changes in age distribution of the population -Changes in survivorship due to treatment -Changes in incidence of disease resulting from genetic factors, environmental factors or prevention (i.e. vaccination)

Direct adjustment procedure

1. Calculate age-specific rates for each population that will be compared 2. multiply age-specific rate times the standard population for each age group 3. This gives the expected number of deaths 4. total number of expected deaths for all age groups 5. Divide expected total by the total standard population

Steps of an Outbreak Investigation

1. Determine existence of epidemic 2. Confirm diagnosis 3. Define a case and count cases 4. Orient data in terms of person, place, time 5. Determine who is at risk of becoming ill 6. Develop hypotheses and test them 7. Compare hypotheses with established facts 8. Plan a more systematic study 9. Communicate findings/Prepare a written report 10. Implement control and prevention

Non-infectious reportable conditions

1. Injuries (hospitalized) - Burns - Spinal cord injuries - Drownings - traumatic brain injuries - work-related deaths - violent deaths (homicide/suicide) 2. Occupational - Asbestosis - Lead poisoning Silicosis 3. Cancer 4. Birth defects

Probable Mean, Minimum and Maximum Incubation periods

1. Minimum incubation period = time from last exposure to first case 2. Maximum incubation period = time from first exposure to last case 3. Mean incubation period = time from midpoint of exposure to peak number of cases

Indirect adjustment procedure

1. Multiple standard population age-specific death rates by # in each age group of population to be compared 2. this gives the expected # of deaths 3. Sum the expected number of deaths 4. Calculate SMR = observed/expected 5. To calculate the indirect standardization mortality rate --> SMR x crude mortality rate for the standard population

Interpretations of SMR

=100 -Observed and expected numbers are the same -Deaths in the study population are similar to reference population <100 -Observed is less than expected -Less deaths occurred in the study population than would be expected, based on the rates in the reference population >100 -Observed is greater than expected -Greater deaths occurred in the study population than would be expected, based in the rates in the reference population.

Louis Pasteur

A French chemist, this man discovered that heat could kill bacteria that otherwise spoiled liquids (pasteurization) - developed first rabies vaccine - Germ theory

syndromic surveillance

A group of symptoms that collectively indicate or characterize a disease, psychological disorder or abnormality. -Can indicate exposure to chemical biological agent (bio-terror & industrial pollution & early detection of potential epidemics). -Electronic transfer of data fields -Describing symptomatology or presenting complaints Strengths: May provide early recognition of an ID breakout or BT event. Assures ongoing/systematic surveillance is set up properly. Limitations: Numerous software packages, requires compatible electronic formats, may be difficult to define sensitivity to individual or combined measures being used.

Proportion

A ratio in which the numerator is contained in denominator

Rate

A ratio representing change over time

How to interpret adjusting rates...

AFTER ADJUSTING FOR ---- (ex: age, sex, weight etc), group A has a higher death rate than group B.

Data collectors are sent to tobacco shops in OK to observe ads within 3ft of ground. What type of surveillance?

Active surveillance (trained people going to collect data)

Adjusted Rate (standardization)

Adjustment (also called standardization) is used when two (or more) populations have different distributions of a demographic variable such as age, race, sex. The adjusted rate is an artificial summary rate that allows comparisons between populations without the influence of a confounding factor or factors. The rate depends on the standard population used to adjust it. The two common methods of adjustment are the DIRECT and the INDIRECT.

Epidemiological Triangle Example TB

Agent: TB pathogen Host: Individual (poor nutrition, biological and social traits) Environment: Crowding, poor ventilation, bad sanitation

Descriptive epi is hypothesis testing and analytic epi is hypothesis generating. (T/F)

BIG FALSE

Types of pathogens

Bacteria Viruses Fungi Parasites Prions toxins

Cumulative Incidence of cancer

CI: number of new cases during given period of time/population at risk for an event As a general rule, when calculating cumulative incidence we typically use the total population to represent the population at risk - with the understanding that it is our best estimate of the true population at risk.

The summary measure for total population (is it crude, specific, or adjusted)?

CRUDE

Case Fatality Rate

Case Fatality is the rate at which deaths occur from a disease among those with the disease. Ex: Pneumonia (deaths from pneumonia = 1,410) 1,410 / 24,661 (new cases of pneumonia) =0.05718 deaths per case of pneumonia = 5.72 deaths per 100 cases of pneumonia in Oklahoma for the given year.

Cause-Specific Mortality

Cause-Specific Mortality is the rate at which deaths occur for a specific cause per total population Ex: pneumonia (deaths from pneumonia = 1,410) 1,410 / 3,550,000 (estimated population in Okla) =0.000397 deaths from pneumonia per person = 3.97 deaths from pneumonia per 10,000 people in Oklahoma for the given year.

Essence of epidemiology

Comparison

Which of the following is a disadvantage of a crude rate?

Comparisons may be confounded by population characteristics

What are the three type of mortality rates?

Crude Cause-specific Age-specific

Crude Birth Rate

Crude birth rate is the number of live births per average population. Ex: 12.34 live births per 1,000 people in Okla for the given year.

Crude Death Rate

Crude mortality is the death rate within an entire population. Ex: 10.23 deaths per 1,000 people in Okla for the given year.

Robert Koch

Developed the culture plate method to identify pathogens - Vibrio cholera isolated - Koch postulates 1.Microorganism must be in all organisms suffering from disease, but not in healthy organisms. 2.Microorganism must be isolated from diseased organism and grown in pure culture. 3.Cultured microorganism should cause disease when introduced into healthy organism. 4.Microorganism must be reisolated from inoculated, diseased host and identified as being identical to original causative agent.

Watson and Crick

Developed the double helix model of DNA. 1953

Pandemic

Disease that occurs over a wide geographic area and affects a very high proportion of the population.

Ratio

Division of one quantity by another

What is a ratio?

Division of one quantity over another

Mortality rate is a reasonable approximation of the incidence rate of disease when -->

Duration is short and case fatality is high

Person-time

Each person under observation contributes x amount of time to the denominator of an incidence rate only up until their diagnosis/lost to follow up

Epidemic v. Endemic

Endemic is contained within a country or population and epidemic is a disease that affect a large number of a population

Prevalence

Existing number of cases at a specified point in time over a period of time NEW AND OLD

Sentinel surveillance is representative of the whole population? (T/F)

FALSE

A strength of passive surveillance is completeness of reporting. (T/F)

False

denominator for the calculation of incidence density is the count of the population at risk during the specific time. (T/F)

False Person-time at risk

To calculate case fatality, we use the toal population as our denominator. (T/F)

False (people who have the disease)

Hippocrates

Father of medicine - Believed disease was result of imbalance in 4 bodily humors (black bile, yellow bile, phlegm, blood) -Recognized that disease results from physical environment rather than supernatural causes

Epidemiological triangle

Host --> agent --> environment

Mortality Rate

Incidence of deaths in a population

Assuming a steady state, prevalence is approximately equal to -->

Incidence x duration

Type of adjustment method using age-specific rates for selected standard population?

Indirect

What are the two methods of standardization?

Indirect and direct

Infant Mortality Rate

Infant Mortality is the rate of death for children less than one year of age. This rate is based on a denominator of number of live births during the same year.

Secular trends

Long term trends

John Snow

Mapped the occurrence of cholera in London - Father of epidemiology

Maternal Death Rate

Maternal Mortality is the rate of death from childbearing for a given time period based on a denominator of the number of live births during the same time period.

Herd immunity

Means enough people in a population are immune such that it does not spread to susceptible people

A paper published an SMR. What does that mean?

More deaths occurred in the study population than expected

Count

NUMBER of cases of a health event -For a count to be descriptive, it must be considered relative to the size of the group

Neonatal Mortality Rate

Neonatal Mortality is the rate of death of children less than 28 days of age. The denominator is the total number of live births during a given time period.

Incidence

New cases identified over a specified period of time. NEW CASES

SMR

Observed/Expected x 100

Definition of Public Health Surveillance

Ongoing, systematic collection, analysis, interpretation, and dissemination of data regarding a health-related event for use in public health action to reduce morbidity and mortality to improve health

Definition of Public Health

Organized community efforts aimed at the prevention of disease and the promotion of health

Name the surveillance system where reporting sources report at will.

Passive

Descriptive epidemiology describes the distribution of disease related to?

Person, Place, and Time

Ignatz Semmelweis

Physician/Obstetrician Discovered hand-washing after cadavers with medical students reduced mortality by 17% Used chlorinated lime water as antisepsis

Which component of descriptive epi would occupation associate with?

Place

Prevalence proportion: two divisions?

Point prevalence and period prevalence

Point Prevalence of cancer

Point prevalence is prevalence at a selected point in time of the population at same pint in time. (period prevalence is the total number of persons known to be a case during some stated period of time.) = 43,521 (Patients alive with cancer on July 1) /3,550,000 (estimated population as of July 1) = 0.01226 cancer cases per person = 12.26 cancer cases per 1,000 people on July 1 in Oklahoma for the given year.

"Prevalence rate = prevalence proportion"

Prevalence "rate" (aka prevalence proportion) measures the proportion of existing cases in the specified population, which means the numerator includes both new and ongoing cases.

P = I x D

Prevalence = Incidence x Duration

Measures of Disease Frequency

Prevalence and Incidence

Prevalence

Prevalence is the number of existing cases in a specified population at a given point in time.

Proportionate Mortality Ratio for cancer

Proportionate Mortality Ratio (PMR) is the number of deaths from a given cause in a specified time period per 100 total deaths in the same time period. Ex: 7,423 (deaths from cancer)/ 38,100 (total deaths) = 0.1948 deaths from cancer per death = 19.5% of all deaths in Oklahoma for the given year are deaths from cancer.

Which measure of mortality would you calculate to determine the proportion of all deaths attributable to diabetes -->

Proportionate mortality ratio

PHIDDO

Public health investigation and disease detection of Oklahoma system - Online case reporting system to OSDH - Real time disease reporting - Secure internet-based application - ability to update previously submitted reports (Physicians, nurses, infection control practitioners, laboratorians, other healthcare personnel

Rate

Ratio over time TIME TIME

Passive Surveillance

Reports are sent on at will (reports are faxed or mailed from healthcare providers/labs Strengths: Simple, not overly burdensome on public health system Limitations: Completeness of reporting, under reporting is likely. generalities: Less expensive, less human resources required, less assurance about quality and quantity, reports tend to be made late, INCREASED sustainability.

James Lind

Scurvy - Citrus diet

Sentinel Surveillance

Sentinel providers and laboratories selected based on based on geography, population, lab testing capacity. Goals: Identify entry of virus (is it novel or known?), geographic progression, change in virus circulating. Strengths: Valid and reliable, rapid, good for temporal tendencies Limitations: Who does it represent? Labor Intensive.

Six clinics were strategically selected in the OKC area to report flu case. What type of surveillance is this?

Sentinel surveillance (strategically selected).

A paper publishes rates for only Asians within the age group of 21-29. What measure is this?

Specific measure

Crude measures

Summary measures for total population - Crude mortality rate --> overall risk of dying in that population

Type of surveillance system commonly used in early detection of bioterrorism.

Syndromic Surveillance

Prevalence is NOT a measure of risk. (T/F)

TRUE

Crude mortality Rate

The crude mortality rate is a summary measure and represents the probability of dying in a population. It is specific for the population for which it was calculated and can't be used for comparison purposes unless the compared populations have similar distributions of age, sex, race, socioeconomic class, geographic distribution or any other variable that might affect the magnitude of the crude rate.

Specific Rate

The specific rate refers to a rate for a subgroup or category within the population and represents the probability of death for the specific subpopulation. The subgroup may be demographic (age, sex, race/ethnic group) or based on cause (diabetes, lung cancer, AIDS). The specific rates may be used for comparison purposes, however, the use of specific rates is cumbersome since so many groups must be compared.

Direct method of adjustment (direct standardization)

The specific rates in a study population are averaged, using as weights the distribution of a specified standard population. The directly standardized rate represents what the crude rate would have been in the study population if that population had the same distribution as the standard population with respect to the variable(s) for which the adjustment was carried out.

What is epidemiology?

The study of the distribution and determinants of health-related states and events in populations, and the application of this study to control health problems

Indirect Method of adjustment (Indirect standardization)

This method is used to compare study populations for which the specific rates are either statistically unstable because of small numbers, or unknown. The specific rates in the standard population are averaged, using as weights the distribution of the study population. The ratio of the crude rate for the study population to the weighted average so obtained is the standardized mortality (or morbidity) ratio, or SMR. The indirectly standardized rate itself is the product of the SMR and the crude rate for the standard population.

Purpose of Rate Adjustment

To remove the effects of differences in age or other confounding variables when comparing rates from two or more populations. Methods of adjustment can be used for factors such as age, gender, race, social class, smoking status, birth weight, maternal age, etc.

Crude mortality rate measures represent the overall risk of dying in the population for a given time period. (T/F)

True

Descriptive Epidemiology can give us clues on the geographic extent of a disease. (T/F)

True

Incidence density is a true rate. (T/F)

True

Prevalence proportion is the proportion of the population who have disease at a given point in time. (T/F)

True

Sentinel provider and labs are selected based on location, population, and testing capacity. (T/F)

True

With passive surveillance, public health practitioners do not go out into the community. (T/F)

True

descriptive Epidemiology can give us clues regarding the population at greatest risk of the disease of interest. (T/F)

True

Common source graph

Unimodle one peak

zoonotic disease

a disease communicable from animals to humans under natural conditions; also know as zoonosis

Outbreak

an epidemic limited to localized increase in the incidence of a disease or health-related event, e.g. in a town, village, or closed institution. -Two or more cases from different households - Same symptoms or fingerprint

Cumulative incidence (incidence proportion)

assumes that every person in the population of interest is followed for the entire specified or defined period of time. the denominator is commonly defined as the total population of the population of interest number of new cases of a disease during a period of time/population at risk during same period of time x1000

Odds

defined as the probability of an event divided by the probability of a non-event

Attack Rate

number of cases / total number of exposed and at risk

Crude mortality rate

number of deaths in a population/ same population in a given year

Point Prevalence

number of existing cases of a disease at a point in time/total population at same point in time x1000

Period Prevalence

number of existing cases of a disease during period of time/average population during the same period of time x1000

Incidence Rate (Incidence density)

number of new cases during the time period/total person-time at risk during study period Remain susceptible

Anton van Leewenhoek

refined microscope (200X) to see microorganisms (1683) - Documented observations (hired artists to draw observations)

If a treatment shortens the duration of a disease, this would primarily affect -->

the prevalence proportion of the disease P = I x D

Cuase-specififc mortality rate

the rate of death attributable to a specific cause in a population/ same population in a given year

Age-specific mortality rate

the rate of deaths for a certain age group in a population/ same population in a given year

Which component of descriptive epi would secular trends be associate with?

time

Proportion

•A ratio in which the numerator is contained in the denominator

Determine Who is at Risk of Becoming Ill

•After collecting data, defining a case, and orienting data to time, place, and person it should become evident of who is at risk -Community wide -Restaurant attendees -Occupational exposure

Define a Case and Count Cases

•Create a case definition: -Laboratory testing -Symptoms -Time •Quickly develop a line list/questionnaire -Demographics -Symptoms -Laboratory -Exposure history

Develop a hypothesis about exposure and test hypothesis with appropriate statistical methods

•Data analysis -Evaluate risk of illness/association between illness and exposure(s) -Analyze data to determine validity of hypotheses -Analysis depends on study designed used •Must also assess clinical, laboratory, and epidemiologic features of disease

Confirm the Diagnosis

•Determine if clinical specimens have been obtained •If not, recommend that specimens be collected on acutely ill persons -pfge

Communicate Findings

•Document for action -Detail recommendations for prevention and control •Record of performance -Provides input and output measurements for program performance evaluations •Document for potential medical/legal issues •Enhance quality of investigation -Will highlight weaknesses in investigation -May stimulate further inquiry and fact finding •Instrument for teaching

Retrospective Cohort Study

•Historical exposure data •Technique of choice with acute outbreak in well-defined population •Direct assessment of increase risk associated with exposure •Measure of association often Risk Ratio (RR) -Determine which persons became ill •Compare exposures (foods, beverage) between ill and non-ill persons

Compare Hypothesis with Established Scientific Knowledge

•Hypothesis should be consistent with clinical, laboratory, and other epidemiologic facts of investigation

Plan a More Systematic Study

•Improve sensitivity and specificity of case definition -More accurate number of persons at risk -Better defined case count -Additional laboratory testing (serology)

Case Control Study

•People with disease (cases) are compared to people without disease (controls) •Cases and controls should be comparable •Appropriate when population at risk is not known •Measure of association is Odds Ratio (OR)

Execute Control and Prevention Measures

•Recommendations for precautionary measures to prevent further disease -Made by Investigation team -Decision based upon •Etiologic agent •Source and/or suspected vehicle •Population at risk •Difficult decisions often with potentially large economic ramifications

Establish Existence of Outbreak

•Who became ill and their demographics -Names of all symptomatic people -Ages -Genders -Racial background -Contact information for each person •When they became ill -Date of onset -Time of onset -Still currently symptomatic? •What are their symptoms?