Chapter 14

Lecture

Epidemiology

The field of medicine that studies disease or adverse occurrences experienced by populations.

What are the five W’s epidemiologists characterize their work

• Who

• What

• Where

• When

• Why

What is the idea of public health?

Practices and activities designed to prevent diseases or other negative outcomes in a community, a country, or in the world.

Within the U.S. Public Health Services, what center is charged with protecting the public health?

Disease control and prevention (CDC)

Who was the first to collect and use health, disease, and death statistics to improve health?

Florence Nightingale

What did Florence Nightingale do during the Crimean War?

Used her ability to identify patterns and statistics to implement a change in practices.

• Thirty-two out of every 100 soldiers would die, but Florence changed this to 2 out of every 100 died with her institute.

Who is John Snow?

A doctor during London’s Soho neighborhood cholera epidemic (1854) made a map indicating cholera cases in the area to represent his hypothesis for the spread of the disease.

What did John Snow hypothesize?

That water coming from a specific pump harbored the cholera bacterium

• His map showed that cases clustered around a single pump, which was removed, and the epidemic stopped.

When was CDC established and what was its goal?

• 1946

• To slow down the spread of malaria

What is the Epidemic Intelligence Service (EIS)

• Established 1950s

• Scientists that can be quickly activated and sent anywhere in the world to respond to outbreaks

Prevalence of disease

Total number of existing cases with respect to the entire population

Incidence of disease

• Measures the number of new cases over a certain time period

• Also known as case or morbidity rate

Mortalilty rate

Measures the numher of deaths in a population due to a certain disease

Point-source epidemic curve pattern

Infectious agents came from a single source, and all victims were exposed at the same time

Common-source epidemic curve pattern

Exposure to a single source of infection that can occur over a period of time

Propagated epidemic curve pattern

Results from an infectious agent that is communicable from person to person and is propagated over time in a population

• Influencza is a classic example

Index case

The first patient found in an epidemiological investigation

Endemic

An infectious disease that exhibits a relatively steady frequency over a long time period in a particular geographic locale

Sporadic disease

Occasional cases are reported at irregular intervals in random locales

Epidemic

Statistics indicate that the prevalence of endemic or sporadic disease is increasing beyond what is expected for that population

Pandemic

Spread of an epidemic across continents

Four different stages epidemiologists think of when it comes to disease

• Susceptible host

• Subclinical disease

• Stage of clinical disease

• Recovery, disability, or death

Susceptible host

A person who has not yet encountered the agent or the circumstances that will result in an altercation in health

Subclincial disease

Period of time after the exposure occurs where damage is not apparent to the host or health care provider

Clinical disease

Most obvious effects of the disease are visible as signs and symptoms

Three main ways signs and symptoms can play out in clinical disease stage

• Complete recovery

• Remaining symptoms that we refer to as disability

• Death

Screening Test are

• Noninasive

• Cheap

• Easy to perform to detect diseases before symptoms occur

Diagnostic tests are

• More invasive

• More hazardous

• Less patient acceptance

• Have lower accuracy

A positive screening test is usually followed by a more accurate…

Diagnostic-style test

• Example: Pap smears are screening tests for cancer, but a biopsy would be a diagnostic test

Specificity

Determined by how many people it calls positive who are actually negative (false positives)

Sensitivity

Determined by how many people who were positive were incorrectly found negative (false negative)

Causative agents of a partifucal disease is often determined by:

• Using Koch’s postulates

• Molecular techniques (for example PCR)

How is correlation observed

When one of the studied variables changes in the same direction as the other variable, but without more information, an observed correlation does not indicate causation

Randomized control trials (RCTs)

Test exposures that might have positive effects, as opposed to ones that are potentially detrimental

• Giving someone an experimental drug and seeing if they get better

• Good for experimenatal groups

Cross-sectional studies

The two factors (exposure and disease) are collected at a single point in time, with no refrence to which might have occured first

Case-control

A group of people is categorized based on whether they have the condition (outcome) or not. Then both groups are asked about a certain exposure they have had to determine if one exposure stands out in the group with the condition.

Cohort study

People without the condition in question are enrolled in the study and followed over time, monitored both for the appearance of a disease and for several exposure factors that are suspected of leading to that disease.

Main criteria to declare exposure as causative

• Strength of association:

• Consistency of association

• Specificity of association

• Temporality of association

• Biologic Plausibility

Strenght of association

Dependent on statistical analysis and asks how strongly the exposure and the outcome are sometimes associated

Consistency of association

When multiple studies of the same and different designs provide the same result, then we can call the findings

Specificity of association

Refers ot the extent that only one exposure is associated with a disease, or exposure only results in a single disease.

Temporalilty of association

The cause you are investigating can be shown to have occured before the outcome

Biologic plausibility

Traces a biological line between the exposure and the outcome as reinforcing evidence

Check for understanding: The number of new cases of disease over a certain time period is the____

Incidence

Check for understanding:The____rate is the number of persons afficted with infectious disease.

Morbidity rate

Check for understanding: An ____ disease is seen at a steady frequency over a long period of time in a particular location.

Endemic

Check for understanding: An ___ is an epidemic occuring over multiple continents

Pandemic

Check for understanding: Name three study designs that help contribute to understanding causation

• Cohort study

• Case-control study

• Randomized controlled trial (RCT)

Surveillance refers to

Collecting, analyzing, and reporting of data on the rates of occurrence, mortality, morbidity, and transmission of infections

Physicians and hospitals report all________

Notifiable disease that are brought to their attention

Government agency responsible for keeping track of infectious disease is the ____

CDC

What reports does the CDC publish weekly of diseases

Morbidity and Mortality reports

The CDC estimates that every day, 1 in 31 hospital patients and 1 in 43 nursing home residents have an…

HAI ( Healthcare-associated infections)

Top four HAI’s

• Catheter-associated urinary tract infections (CAUTI)

• Central line-assocaited bloodstream infections )CLABSI)

• Surgical site infections (SSI)

• Ventilator-associated events (VA)

Medicare and Medicaid programs stopped reimbursements to hospitals for ______, _______, and ______ aquired during hospital care

• CAUTI’s

• CLABSI’s

• SSIs

Adoption of universal precautions:

• Medical asepsis

• Surgical asepsis

• Infection-control officer

R0 (R-sub-zero or R-naught)

Term to give the basic reproduction rate

• Describes how many susceptible people (on average) that one infected person will spread the infection to

Case fatality rate (CFR)

The number of people who die of the disease divided by the number of people infected

• Based on people who receive no treatment

R-sub-zero and CFR can vary based on

• Geographic location

• Circumstances of an outbreak

• Variant of the microbe

• Vaccinations are most needed for high R-sub-zero disease

What plays a critical role in controlling infectious disease

Vaccines

Herd immunity

When a significant portion of a population becomes immune to an infectious disease, it limits further disease spread

Vaccine Adverse Events Reporting System (VAERS)

Centralized system for reporting and advertising events happening after a vaccination

Who can make a report whether the adverse effect is related to the vaccine or not?

• Patients

• Parents

• Healthcare providers

Emerging disease

Caused by newly identified microbes

• Examples: SARS and novel strains of influenza

Reemerging disease

Those that have affected the human population in the past but are now becoming more prevalent due to travel, habitat invasion, or the development of drug resistance.

Global Disease Detection (GDD) service

Collaboration between the CDC, the WHO, and the local governments all around the world to monitor disease emergence and to spot and limit epidemics

CDC also

• Monitors developing situations in health and disease

• Creates strategies to decrease excess morbitidty and mortality

What disease is caused by Trypanosoma Cruzi

Chagas disease

What disease is caused by the tapeworm Taenia solium

Neurocysticercosis

What is caused by worms that travel through tissues and can cause blindness

Toxocariasis

What infected 60 milllion people in the United States

Toxoplasmosis

What is a protozal infection of the genital tract that leaves those infected more vulnerable to other sexually transmitted infections and leads to premature births in infected mothers?

Trichomoniasis