pubh exam 3

6, 7, 8

Which of the following is true of tests used for screening for disease?
1. One positive screening test usually is not sufficient to diagnose a
disease.
2. Changes within the range of normal test results may be due to
disease presence.
3. The range of normal is not the same for all individuals, groups or
populations.
4. All of these are correct.

4. All of these are correct.

Which statement best describes the mortality due to drug overdoses in
the United States?
1. Deaths from motor vehicles exceed deaths from drug overdoses.
2. Deaths from drug overdoses implies willful intent of victims.
3. Deaths from drug overdoses has declined in recent years.
4. None of the above.

3. Deaths from drug overdoses has declined in recent years.

Why is lung cancer considered a ’serious’ illness?
1. It accounts for substantial morbidity and mortality.
2. Treatment is well-established.
3. It is easily detected.
4. All of the above.

1. It accounts for substantial morbidity and mortality.

Which of the following statements is true about QALYS?
1. A QALY may be interpreted as a year of life at full health compared
to immediate death.
2. QALYs take into account the number of life-years saved.
3. In economic analyses, the cost of an additional QALY of less than
$50,000 is considered to be cost-effective in the U.S.
4. All of the above are correct.

4. All of the above are correct.

Which of the following can be considered cost-effective?
1. An intervention that reduces the cost while increasing the net-
benefit of care.
2. An intervention that reduces the cost and net-benefits of care.
3. An intervention that increases net benefit, but increases cost of
care.
4. An intervention that reduces cost of care

1. An intervention that reduces the cost while increasing the net-benefit of care.

public health framework for differentiating disease and disability

by separating a "health condition" (which includes disease) from "disability," which is an umbrella term for impairments, activity limitations, and participation restrictions

• Disease is seen as an interruption of normal body function (pathology) or a health condition itself

• Disability results from the interaction between this condition and environmental factors, and the individual's resulting limitations in daily activities and social roles

non-communicable diseases (NCDs)

chronic conditions that do not result from acute infectious processes and are not communicable

• a disease that has a prolonged course that does not resolve spontaneously and for which a complete cure may be difficult to achieve

characteristics of non-communicable disease

• complex (multifactorial) causes

• long latency period

• prolonged course of illness

• functional impairment/disability 

• common etiologies across similar conditions

coronary heart disease

problems with blood vessels supplying the heart muscles

cerebrovascular disease

problems with blood vessels supplying the brain

peripheral arterial disease

problems with blood vessels supplying the arms and legs

congenital heart disease

malformation of heart structure

Cardiovascular disease risk factors - major modifiable factors

• tobacco use 

• hypertension

• hyperlipidemia

• physical inactivity/obesity

• unhealthy diets

• diabetes

• ? : 

  • SES, mental heal, heavy alcohol use, medication use, personality

Cardiovascular disease risk factors - non modifiable factors

• age

• gender

• heredity

• race/ethnicity

• inflammatory markers

cancer

30-50% due to lifestyle

proliferative cell growth beyond usual boundaries

• benign : non cancerous

• in-situ : localized and has not spread from where it started

• invasive : spread from original location to surrounding tissue

cervical cancer risk factors

HPV infection, smoking, family history, poverty, no PAP test

lung cancer risk factors

tobacco, radiation, asbestos, radon, air population

great cancer risk factors

reproductive hormones, weight, race, age

colorectal cancer

age, diet, family history

diabetes

disorder of the metabolism

• gestational

• glucose intolerance

  • type1 (10%) : genetic/biological

  • type2 (90%) : biological & sociological

diabetes - major modifiable factors

• unhealthy diets

• physical inactivity

• obesity/overweight

• hypertension

• high cholesterol

• ? : 

  • low birth weight, SES, mental health, heavy alcohol use, heavy sugar consumption, light fiber consumption

Chronic Obstructive Pulmonary Disease (COPD)

90% of deaths are in low to middle income countries

two main conditions that make it up : 

• chronic bronchitis

  • inflammation of the airways and a persistent cough with mucus

• emphysema

  • involves damage to the air sacs in the lungs, leading to SOB

major stages in the disease process

disease absence, disease onset, disease symptoms, disease diagnosis, disease treatment, disease outcome

principle mechanism for chronic disease control : secondary prevention to detect re-symptomatic disease

disease screening 

• the application of simple medical tests/procedures with asymptomatic individuals in search of evidence of pathology/disease

blood pressure, BMI, weight and waist circumference, skin checks, cholesterol, bloop pressure, vision, hearing, STIs, substance use, urinalysis, cancer, mental acuity, diabetes

• a presumptive judgement distinguishing apparently well persons from actually well persons

• intention to be efficacious (results influences clinical decisions) and effective (results influence disease course)

why screen? secondary prevention

• disease is serious

• disease has an asymptomatic period for early detection

• early detection improves survival, reduces morbidity, lowers costs

• public is willing to be screened

why not screen? secondary prevention

• yield is low (resources expended on persons who do not benefit)

• biological and test variability makes screening results less reliable 

• false security with false negative results delay diagnosis and treatment 

• unnecessary intervention with false positive produces unnecessary stress/anxiety, pain/discomfort, expense, inconvenience, and/or pathological exposures 

• end results are unchanged

true positive : screen works

the diagnostic gold standard determines : disease present

the screening test result suggests : disease present

false positive : screening fails

the diagnostic gold standard determines : disease is absent

the screening test result suggests : disease is present

the gold standard

the most definitive or accurate diagnostic method available for a specific disease, used as a benchmark to compare other tests against.

screening test

is a quick, preliminary test to identify individuals at increased risk for a disease

false negative : screening fails

the diagnostic gold standard determines : disease is present

the screening test result suggests : disease is absent

true negative : screening works

the diagnostic gold standard determines : disease is absent

the screening test result suggests : disease is absent

the efficacy of a test is judged by

how well it identifies diseased and non-diseased cases

• measures by concepts of sensitivity and specificity

a test is considered sensitive when

it is good at identifying disease when it is present

a test is considered specific when it is

good at identifying non-disease when there is no disease

sensitivity

true positive / (true positive+false negative)

specificity

true negative / (true negative+false positive)

the effectiveness is a test is judged by

how well it predicts whether a person has or does not have a condition

a test with a Positive Predicative Value (PPV+)

when a positive result is indicative of the presence of a condition

a test has a Negative Predicative Value (PPV- or NPV)

when a negative result is indicative of the absence of a condition

PPV+

TP / (TP+FP)

PPV-

TN / (TN+FN)

positive predictive values are

higher when specificity (ability of the test to correctly identify those without the condition is high) and prevalence of the condition is low

negative predictive values are

higher when sensitivity (ability of the test to correctly identify those with the condition is high) and prevalence of the condition is high

efficacy and effectiveness of screening : the necessary trade offs

1. in the interest of achieving high sensitivity, a test tends to have low specificity 

• its really important to find cases

2. in the interest of achieving high specificity, a test tends to have low sensitivity 

• it’s really important to exclude individuals 

3. in order for a test to be sensitive it will necessarily identify a fair number of false positives in the course of capturing many true positives 

• therefore the positive predictive value of a sensitive test tends to be low 

4. in order for a test to be specific, it will necessarily identify a fair number of false negatives in the course of excluding true negative 

• therefore, the negative predictive value of a specific test tends to be low

Deciding who is ill and who is not is

both a scientific and social consideration

• Persons who are considered ill have different rights and responsibilities than persons who are not
  ill

• We want to distinguish the two groups, but the screening tool necessarily will produce
  errors (declaring some health people ill and some ill people healthy)! 

lowering the screening threshold

captures more ill persons, BUT misclassifies many healthy people as ill

raising the screening threshold

captures more healthy persons, BUT misclassifies many ill persons healthy

sensitivity?

369 / 384 = 0.961

specificity?

558 / 616 = 0.906

positive predictive value

369 / 427 = 0.864 (86.4%)

negative predictive value

558 / 573 = 0.974

what is true of HIV

• It has a longer incubation period than influenza.

• It can be transmitted before it can be detected by commonly used antibody
  tests.

• Drug treatment can reduce the degree of communicability.

which characteristic of infectious disease is reflected in the following
statement? “Hepatitis B can survive for extended periods of time in
contaminated needles.”

Persistence in the environment is evident

which disease is the least likely to be eradicated?

influenza

what is true of tuberculosis (TB)

• Tuberculosis may remain contained in the body for decades without causing
  disease.

• Isolation has been used in the past as a major strategy for controlling the
  spread of TB.

• People with AIDS are at increased risk of developing active TB

What has been successfully used to control communicable
diseases?

• Contact tracing

• Isolation

• Treatment upon exposure

Communicable disease:

illness due to a microorganism such as bacterium, parasite or virus that is transmitted person-to-person or animal/physical environment to humans via air, water, fomites, insect or animal bites

Non-Communicable Disease (NCDs) that can be influenced or triggered by
infectious agents:

• Cervical cancer, for example, is caused by the Human Papilloma Virus
(HPV).
• Liver cirrhosis and cancer can be the byproduct of Hepatitis B and C.
• Stomach cancer is associated with H pylori infection.
• Heart health may be compromised by a history of COVID-19
• Heart attack and stroke may be triggered by Influenza
• Rheumatic heart disease can be caused by streptococcal infection.

Communicable diseases that can be influenced or triggered by NCDs

• Smoking and diabetes can increase the risk of tuberculosis.
• HIV treatment can increase the risk of cardiovascular disease.
• Malnutrition can make individuals susceptible to HIV, TB, Malaria, etc

biological sources of communicable diseases

• bacterium

• viruses

• fungus

• parasite

bacterium

single-celled microorganism able to exist free-living as a parasite

virus

microorganisms unable to exist independent of living cell

fungus

spore-producing organisms that feed on organic matter

parasite

organism living in, on, or with another organism in order to obtain nutrients

examples of bacterial infections

salmonella, e.coli, bubonic plague, MRSA

examples of viral infections

• varicalle —> chicken pox

• rubella —> measles

• pertussis —> whooping cough

examples of fungal infections

• tinea pedis - athlete’s foot

• candidiasis - thrush

• tinea corpori’s - ringworm

parasite infections

guinea worm disease

pinworm disease

vectors

an organism that is usually an arthropod like a mosquito or tick, that carries and transmits infectious agents such as viruses, bacteria, or parasites between hosts

• bedbugs, Lyme disease

dengue fever

Virus caused by the bite of infected Aedes mosquitoes.

• While many cases are mild, causing flu-like symptoms, severe can lead to serious complications like hemorrhaging, shock, and death.

• no specific cure, but treatment focuses on managing symptoms with rest and fluids

tick-borne illnesses

bacterial, viral or parasitic diseases spread through the bite of infected
ticks.

• Symptoms can vary but often include fever, headache, fatigue, and muscle aches

fomites

inanimate objects that can transmit infectious microorganisms
and be the source of disease

• Common infections: MRSA, Adenovirus, Coronavirus, hand, foot, and mouth
  disease, Influenza, Norovirus, Rhinovirus, and Rotavirus

sporadic

unexpected, infrequent, irregular

endemic

expected, regular, indefinite, bounded

epidemic

unexpected, abnormal, finite, bounded

pandemic

unexpected, abnormal, irregular, finite, unbounded

Ignaz Semmelweis (1818-1865)

emphasized handwashing with chlorinated lime water to reduce maternal mortality from puerperal fever

John Snow (1813-1858)

stopped a London cholera outbreak by limiting access to a contaminated public water supply.

Joseph Lister (1827-1912)

introduced antiseptic methods in surgery, based on Pasteur's findings, to prevent wound infections.

communicable disease framework - how do conditions that cause disease relate?

Agent, Host, Environment

Agent - communicable disease framework

factor(s) external to the individual capable of causing disease, illness

host - communicable disease framework

the individual capable of acquiring disease, illness

environment - communicable disease framework

the setting in which the agent and host come into contact

10 steps in outbreak investigations

• Establish the existence of an outbreak
• Prepare for fieldwork
• Verify the diagnosis
• Define and identify cases
• Use descriptive epidemiology to assess burden to population
• Develop causal(transmission) hypotheses
• Use analytic epidemiology to evaluate the hypotheses
• Refine hypotheses
• Implement control and prevention measures
• Communicate findings to the public

infectivity

ability of a bacteria, fungi, parasites or virus to enter into a living organism through horizontal transmission

direct contact

spread of infectious organism from one person to other

indirect contact

spread of infectious organism by individual coming in contact with contaminated object

modes of infectious transmission

airborne, soil, blood-borne, droplet, diet, zoonosis, oral, sexual contact, vector, bites, fomites

airborne - modes of infectious transmission

anthrax, measles, TB, smallpox, varicella

soil - modes of infectious transmission

tetanus, intestinal worms

blood borne - modes of infectious transmission

HIV/AIDS, hepatitis C

droplet - modes of infectious transmission

pneumonia, flu, pertussis, TB, mumps, chickenpox

diet - modes of infectious transmission

e.coli

zoonosis - modes of infectious transmission

avian flu, swine flu

oral - modes of infectious transmission

choler, hepatits A, polio, rotavirus, salmonella

sexual contact - modes of infectious transmission

gonorrhea, herpes, chlamydia

vector - modes of infectious transmission

malaria, yellow fever

bites - modes of infectious transmission

bubonic plague, rabies, cat-scratch fever