IPHY 3490 CU Boulder Final Exam

sporadic

A disease that occurs infrequently and irregularly

Endemic:

Continuous occurrence at and expected frequency over a certain period and in a certain geographical location

Outbreak

a localized disease epidemic ( in town or community)

Epidemic

The occurrence of a disease that is greater than the expected in a certain geographical regions

Pandemic

-When the epidemic is generalized and involves different countries in a large population

Explain why epidemics occur.

1. When susceptible individuals (not vaccinated or otherwise immune) travel into an endemic area where the infectious disease exists

2. When a preexisting infection occurs in an area of low endemicity and reaches susceptible persons as a result of new or unusual social, behavioral, sexual or cultural practices

3. When contamination of food, water, or other vehicles takes place by an agent not normally present

4. When host susceptibility and response are modified by natural or drug-induced immunosuppression (cancer treatment), malnutrition or disease such as AIDS

5. Natural evolution of an infectious agent (usually a virus) to which humans have no immunity

What are the the four components of the epidemiologic triangle?

-A model used to explain the etiology of infectious diseases

-Recognized four major factors in the pathogenesis of disease:

1. host

2. agent

3. environment

4. time

Infectious Disease Agent

-Microorganism capable of producing an infectious disease

-Microbiology: the study of infectious disease agents

-Must be present for an infectious to occur

Host:

-A person or animal that is susceptible to disease

-Once an agent infects the host, the degree and severity on the infection will depend on the host's ability to fight off the infectious agent

Two types of defense mechanisms are present in the host:

1. Innate response - macrophage

2. Adaptive responsive - T and B lymphocytes

Acquired immunity can help too

Environment:

-The domain in which disease-causing agents may exists, survive, or originate

1. Physical environment (weather, temperature, humidity, etc.)

2. Social environment (behavioral and cultural characteristics of a group of people)

3. Reservoirs foster the survival of infectious agents:

Time

- Incubation Period

- generation period

Characteristics of Infectious Agents

-infectivity

-pathogenicity

-virulence

infectivity

Ability to cause infection: Capacity of an agent to enter and multiply in a susceptible host and thus produce infection or disease

pathogenicity

-Ability to cause clinical disease: Capacity of an agent to cause active clinical disease in the infected host

- = total # of cases with clinical disease / total # of exposed to infection

virulence

-Degree of pathogenicity

-Severity of the disease after infection occurs

- = total # of cases with clinical disease / total # infected cases (subclinical → severe)

Clinical disease:

Obvious observable or detectable symptoms (mild → moderate → severe → death)

vertical transmission

From mother to child

-Mammary glands (milk)

-Placenta (blood)

-Vagina (secretion, blood)

Define the iceberg concept of infection

Active clinical disease (tip of the iceberg) accounts for a relatively small proportion of the host's infection and exposure to disease agents

There are diff levels of disease that can occur

Describe the chain of events after exposure to an infectious disease agent

Reservoir(portals of exit) -> mode of transmission -> susceptible host (portals of entry)

Horizontal Transmission - direct

From infected individual to another susceptible individual- person to person

Direct contact

- skin to skin contact

- exchange of bodily fluids

- large droplets: sneezing, coughing, talking closely

Horizontal transmission - Indirect

via any sort of intermediary, animate or inanimate

Airborne, vector borne or vehicle born

Airborne transmission:

Infectious agents are carried by dust or droplet nuclei suspended in air

Vector borne (animate intermediates):

-Vector: a living insect or animal involved with transmission of the disease agent

-Ex: mosquitos and malaria

Vehicle borne (inanimate objects):

-Vehicle: an inanimate object involved with transmission of the disease agent such as water, food, soil, fomites

-Fomites: objects or materials which are likely to carry infection (doorknob, clothing, unsterilized medical equipment, unwashed hands, etc.)

-A → B → C

--A indirectly transmits agent to C through an intermediary source (B)

natural, active immunity

-Transfer of protective immunity: natural, active (natural immunity):

1. Results from an infection by the agent

2. Leads to antibody production in the host → long lasting immunity

artificial, active immunity

-Transfer of protective immunity: artificial, active (vaccine-induced immunity):

1. Results from an injection with a vaccine that stimulates antibody production in the host

2. Long lasting immunity

3. How do vaccines work? - inject weakened or killed version into the body so we can form antibodies against it if actual pathogen was ever to attack

natural, passive immunity

-Transfer of protective immunity: natural, passive:

1. Preformed antibodies are passed to the fetus during pregnancy and during breast feeding

2. Provides immediate, temporary protection to the newborn

artificial, passive immunity

-Transfer of protective immunity: artificial, passive:

1. Performed antibodies are given to exposed individuals to confer protection against a disease

2. Provides immediate temporary protection

asymptomatic (healthy) carrier

People with inapparent infections (asymptomatic ore healthy carriers) never develop and illness but can transmit their infection to others

Incubatory carrier

-Incubatory carriers are people going to become ill but begin transmitting their infection before their symptoms start

1. A person infected with measles begin to shed the virus in nasal and throat secretions a day or two before any cold symptoms or rash are noticeable

2. Most notable, HIV infection may be present for years before the person develops any symptoms

Convalescent carriers

-Convalescent carriers are people who continue to be infectious after their recover from illness

1. This happens with many diseases

2. Salmonella patients may excrete the bacteria in feces for several weeks, and rarely even for a year or more

Chronic carriers

-Chronic carriers are people who continue to harbor infections for a year or longer after their recovery

1. The chronic carrier state is not uncommon following Hep B infection, whether or not the person became ill, and may be lifelong

generation time

1. Time interval between exposure to an infectious agent and the maximal infectivity of the host

--Can precede the development of active symptoms

2. Useful for describing the spread of infectious agents that have large proportions of subclinical cases

3. Applies to both inapparent and apparent cases of disease

incubation period

1. The time interval between exposure to an infectious agent and the appearance of the fist signs and symptoms of disease

2. How much time has it been since you were infected that you start to show symptoms

3. Provides a clue to the time and circumstance of exposure to the agent

common source

point source, continuous common source, intermittent source

point source

-Persons are exposed to the same common source over a brief period (e.g., single meal or event)

-Majority of cases occur within one incubation period

-Ex: E. coli outbreak 2015 Chipotle

continuous common source

-Exposure is NOT confined to one point in time (prolonged over days, weeks or years)

-Last more than one incubation period

-Ex: Cholera outbreak in UK

intermittent source

-Similar to continuous but exposure is intermittent

-Multiple peaks

-No relation to the incubation period (e.g., contaminated food product sold over period of time)

propagated source

1. Does NOT have common source but instead is caused by spread of infectious agent from one susceptible person to another

2. Transmission may occur directly or via an intermediate host

3. Multiple peaks separated by one incubation period

attack rate (%)

-The proportion of a group that gets the disease under study over a given period

-Reserved for infectious disease outbreaks

--Acute infectious disease outbreaks (food borne illnesses, other acute infectious diseases)

--Acute exposures of large groups to toxic agents

secondary attack rate (%)

-An index of the spread of disease in a family, household, dwelling unit, dormitory or similar circumscribed group

-A measure of infectivity

case fatality rate (CFR) (%)

-Proportion formed by the number of deaths caused by a disease among those who have the disease during a time interval

-Index of the virulence of a particular disease within a specific population

-How many people who had disease X died from disease X?

basic reproductive rate (R0)

-A measure of the number of infections produced on average by an infected individual in the early stages of an epidemic when virtually all contacts are susceptible

--Super spreaders infect more than average

-Can be used as a measure of the transmissibility (contagiousness)

index case(s)

case that first comes to attention of public health authorities

coprimaries

cases related so closely in time that they are considered to belong to same generation of cases

initial case

index case(s) + coprimaries

secondary case

person(s) who become ill after a disease has been introduced into a population and who become infected from contact with a primary case

ways to control the source of the agent

1. agent control:

-remove the source of contamination

-remover at risk persons from exposure

-inactive or neutralize agent

-treat infected persons

2. interrupt the transmission

-transmission control

-improve personal sanitation

-practice respiratory hygiene

-maintain social distance

3. control or modify the host response to exposure

control or modify the host response to exposure

modify behavior or use a barrier

herd immunity

-Immunity of a population, group, or community against an infectious disease when a large proportion of individuals are immune either through vaccinations or prior infection

-For it to work, the majority of the population must be immune (i.e., vaccinated or recovered from illness)

Investigation of infectious disease outbreaks:

Step 1: Establish the existence of an outbreak

Step 2: Verify the diagnosis

Step 3: Construct a working case definition

Step 4: Find cases systematically and record information

Step 5: Perform descriptive epidemiology

Step 6: Develop hypothesis

Step 7: Evaluate hypotheses epidemiologically

Step 8: Reconsider, refine, and re-evaluate hypothesis

Step 9: Implement control and prevention measures

Step 10: Communicate findings

active surveillance

Telephoning or visiting the facilities to collect information on any addition cases

passive surveillance

Sending letter describing the situation and ask for report of similar cases

Primordial Prevention

Avoid the development of risk factors in the fist place, early in life

Primary Prevention

Keeps the disease process from becoming established be eliminating or reducing causes of disease or by increasing resistance to disease

Secondary Prevention

-Interrupts the disease process before it becomes symptomatic

-The presumptive identification of unrecognized disease or defects by the application of tests, examinations, or other procedures that can be applied rapidly

-Positive screening results are followed by diagnostic tests to confirm actual disease

Tertiary Prevention

Limits the physical and social consequences of symptomatic disease

Screening test

- presumptive identification of unrecognized disease or defects by application of tests, examinations or other procedure that can be rapidly applied

- positive screening results are followed by diagnostic tests to confirm actual disease

- To detect potential disease indictors, results indicate suspicion of disease

-Target large numbers of asymptomatic individuals

-Simple and cheap

Diagnostic test:

-To establish presence/absence of disease

-Target single symptomatic individuals, or asymptomatic individuals with positive screening test

-may be invasive and costly

- provide definite diagnosis

what do we screen for?

1. cardiovascular disease

-Blood pressure (SBP/DBP)

-Cholesterol (LDL, HDL, Total)

2. Cancer

-Mammography (breast)

-Prostate specific antigen (prostate)

-Colonoscopy (colon cancer)

3. Mental/Cognitive Health

-Mini-mental state exam (dementia)

-Hamilton depression rating scale (depression)w

When do we not screen?

We can overdiagnose - specially for cancer

- false positives can cause additional stress and follow up tests that may be unnecessary

We often do things bc we can not because we should

Appropriate situation for screening - social

Health problem should be important for individual and community

Diagnostic follow up and intervention should be available to all who require them

Always a favorable cost-benefit ratio

Public acceptance is high

Appropriate situation for screening - scientific

Natural history of condition should be adequately understood

Knowledge base exists for efficacy of prevention and occurrence of side effects

Prevalence of disease is high

A

Appropriate situation for screening - ethical

Program can alter natural history of condition in a significant proportion of those screened

Suitable, acceptable testing for screening and diagnosis of the condition are well accepted, effective methods of prevention are available

Types of Screening Tests:

1. Mass (population) screening

2. Selective (targeted) screening

Mass (population) screening

-Screen entire population regardless of risk status

-Example: measure temperature at airport to identify people who may be harboring a deadly infectious disease such as Ebola

Selective (targeted) screening

-Screen specific groups who are high risk for disease

-Example: HIV screening for sex workers or IV drug users

Describe the five characteristics of a good screening test.

1. Simple: Easy to learn and perform

2. Rapid: Quick to administer

3. Inexpensive: Favorable cost-benefit ratio

4. Safe: No harm to participants

5. Acceptable: Target population will use the test

Reliability (precision)

The ability of a measuring instrument to give consistent results on repeated trials

Validity (accuracy)

The ability of a measuring instrument to give a true measure

Interrelationships Between Reliability and Validity

-It is possible for a measure to be highly reliable but invalid

-It is not possible for a measure to valid but unreliable

sensitivity

Proportion of people who test positive among all those who actually have the disease

specificity

Proportion of people who test negative among all those who actually have the disease

predictive value (+)

The probability that following a positive result, the individual will truly have that disease

predictive value (-)

The probability that following a negative result, the individual will truly not have the disease

accuracy of screening test

The degree of agreement between the screening test and the gold standard diagnostic test

Prevalence

The number of existing cases of a disease or health condition in a population at a point or during a period of time

Relationship Between Sensitivity and Specificity:

1. To improve sensitivity, the cut point used to classify individuals as diseased should be moved towards the range of the normal (A ← C)

- Almost all of the individuals that have the disease wi8ll be screened as positive

2. To improve specificity, the cut point should be moved towards the range typically associated with the disease (A → C)

- Almost all of the individuals that do not have the diseased will be screened as negative

Procedures to Improve Sensitivity and Specificity:

-Retrain screeners: reduces the amount of misclassification in tests that require human assessment

-Recalibrate screening instrument -- reduces the amount of imprecision

-Utilize different test

-Utilize more than one test

How can the predictive value of screening vary with the prevalence of a disease?

When prevalence decreases, the predictive value (+) decreases and the predictive value (-) increases

Sources of bias in screening:

1. lead time bias

2. length bias

3. selection bias

lead time bias

The perception that the screen-detected case has longer survival because the disease was identified early

length bias

Disease identified through screening has slower, less aggressive course and therefore better prognosis (Particularly relevant to cancer screening)

selection bias

Motivated participants have a different probability of disease than do those who refuse to participate

Define environmental epidemiology

Refers to the study of diseases and health conditions (occurring in the population) that are linked to environmental factors

- enviro exposures out of control of exposed individual

What are notable health hazards?

Hazardous waste sites

Air pollution

Nuclear facilities

Drinking water

Healthy worker effect

employed populations tend to have a lower mortality rate than the general population

- this may reduce the measure of effect for an exposure that increases mortality or morbidity

End points for occupational exposures

Morbidity

- self reported symptoms

- results of clinical examination

Mortality

- compare mortality rates in exposed vs nonexposed workers in same industry

Defined hazard surveillance

Characterization of known physical, chemical and biology agents in the workplace

Sentinel health event

a case of unnecessary disease, unnecessary disability, or untimely death whose occurrence is a warning signal that the quality of preventive or medical care may need to be improved

Methodological difficulties assoc with research on enviro health effects

Include complex mixture of substances

Studies may not adequately control for confounding factors

Long term effects of exposure difficult to measure

Effect of low level exposures are difficult to demonstrate

Small study sample

Air pollution: small increase in risk of death from passive smoking is difficult to demonstrate, exposure to cig smoke from many sources, short term vs long term exposure, long latency period btw exposure to cigs and onset of disease

Which mode disease transmission: A newborn was recently infected with syphilis

A. Horizontal - direct

B. Horzizontal - indirect

C. Vertical

D. A and B

E. All of the above

C. Vertical - mother passed onto newborn

Which mode disease transmission:A young girl was recently infected with salmonella

A. Horizontal - direct

B. Horzizontal - indirect

C. Vertical

D. A and B

E. All of the above

B. Horizontal - indirect

- vehicle borne : food contamination

Which mode disease transmission: A women was recently infected with HIV

A. Horizontal - direct

B. Horzizontal - indirect

C. Vertical

D. A and B

E. All of the above

D. A and B - horizontal direct or indirect

Which mode disease transmission: A unvaccinated boy was recently infected with rabies

A. Horizontal - direct

B. Horzizontal - indirect

C. Vertical

D. A and B

E. All of the above

A - horizontal - direct

*rabies is always direct, vector borne refer to insects usually

What type of epidemic spread: about 147 cases of measles infection over 42 days at Disneyland; no external source identified (incubation period ~ 10-12 days)

Propagated source

- *no external source

- last more than 1 incubation

What type of epidemic spread: twenty cases of rotavirus infection over 4 weeks traced to contaminated toys in two daycare centers (incubation ~ 24-72 hours)

Common Source - continuous

*common source = day care

*last longer than 1 incubation

What type of epidemic spread: In Sept and Oct 2001, anthrax was sent via anonymous letters to new agencies in Florida. NY and Wash. 5 people died and 17 become ill shortly after (median incubation ~ 10 days)

Common Source - intermittent

*common source = letters

*intermittent exposure

T or F: You can catch influenza from going out in cold weather without a coat, with wet hair or by sitting near a drafty window

False