PHSC Quiz 3

Epidemiology

Study of population disease

How epidemiologists investigate an outbreak

Confirm→describe→determine cause→control

• Verify diagnosis

  • Clinical symptoms and lab confirmation

• Case definition

  • Mapping time/person/place

• Source identification

  • Pathogen or contaminant

• Education

  • Behavioral, vax, environmental, isolation, meds

Total population

Everyone in a particular population

• Candidate (at risk) population 

• People in the total population who could get the disease/condition of interest 

• Excludes those who have the disease or who are immune

• Example: candidate population for COVID-19 excludes currently positive ppl and those who had it in the past 2 weeks

Prevalence

Measures of disease frequency -  measures the frequency of existing disease in the total population

• Proportion of the total population that has a disease (or other health outcome)

Incidence

Measures of disease frequency - measures occurrence of new cases of disease that develop in a candidate population over a specified time period; describes the risk

the epidemiologist's bathtub

Relationship between incidence and prevalence:

Prevalence depends on incidence and duration of disease.

• Existing water in bath = prevalence

• If we get more cases (faucet adding water) = incidence/new cases coming in

• If nothing else changes as the incidence increases, the prevalence increases too

• Death and recovery are co-occurring factors with prevalency

• Prevalence depends on incidence and duration of disease

Epidemiological study designs

1. Cross-sectional study

2. Cohort study

3. Case-control study

4. Intervention study (intervention/clinical trial)

   1. All epidemiology studies, except fro intervention studies, are observational

Cross-sectional study

• Collecting a cross-section of the population, a snapshot

• sample at one point in time: exposure and outcome are assessed at the same time

• Measure existing disease and current exposure levels 

Cohort Study

• Longitudinal studies

• Measure exposure & follow people over time and see who develops disease

• Know timing and strength of exposure and disease

Case-control study (retrospective)

• Sample cases and controls

  • People who have the disease (cases)

  • People who do not have the disease (control)

• Compare exposure among cases with exposure among controls

• Retrospective study 

Intervention Study

• Same as clinical trial in medicine

  • Vaccines

  • New pharmaceuticals

  • Public health programs that promote healthy diet & exercise, safe sex, mental health support, education, etc. 

• Randomly assign groups (Randomized Control Trial)

  • Treatment or experimental vs control

  • Treat equally in all respects EXCEPT the intervention

• Blinding 

  • Minimize bias

  • Double blind: Neither participants nor study administrators know which individual is receiving intervention 

How do vaccines work?

• Vaccines reduce the risk of infection by working with the body’s natural defenses to safely develop immunity to disease

  • A weakened or killed form of the disease is injected into the body

  • The body creates antibodies to fight the germs

  • If the actual disease germs ever attack the body, the antibodies return to destroy them

• Primary antibody response

• The antibody concentration rises gradually and peaks about 2 weeks after vaccination

• Secondary antibody response: the antibody concentration rises quickly, and the response is more intense. The antibody concentration remains higher for longer

Herd immunity

• Why you get vaccinated for those around you like babies (newborn) who can’t get vaccinated

• No one is immunized→ contagious disease spreads through the population

• Some of the population gets immunized→ contagious disease spreads through some of the population

• Most of the population gets immunized→ spread of contagious disease is contained

• Herd immunity number: percent of population that needs to be vaccinated in order to protect those who are unvaccinated

  • Diphtheria: 85%

  • Pertussis: 92%

  • Measles: 95%

  • COVID-19: ?? → not enough people got vaccinated to know (only like 67% dud due to conspiracy theories and anti-vaccination theories)

Vaccine hesitanc

• There is a recommended schedule of what vaccine babies/children should get and when they should get it

  • RFK Jr (new HHS secretary) wants to make changes in this schedule

  • New change already: no more Hep B birth dose!

• One of the top 10 global health threats according to the WHO

• Disproportionately impacts health of children in low and middle income countries (LMICs)

• Is growing in the US

• It was a problem before the pandemic; but pandemic definitely made it worse

Vaccines and Autism: No link!

• Wakefield study (1998) linked vaccines and autism: essentially started anti vax theories

  • Based on 12 children, published in the Lancet

  • Parent and doctor reports of timing of effects

• No link found between MMR (measles) vaccine and autism

  • >17 million children

  • 27 cohort studies, 17 case control studies, 5 time series trials, 2 ecologic studies, 6 case series studies

• Wakefield study was retracted in 2011 – main author falsified data-FRAUD

• Most of Wakefield’s co-authors withdrew their names from the study in 2004 after learning he had been paid by a law firm that intended to sue vaccine manufacturers

• But damage to vaccine confidence had been done: news headlines, promotion from Hollywood

  • Crazy people believed cases of 12 cases over the other 17 million children

Vaccine exemptions

• 47 states allow exemptions from school vaccination requirements for religious and/pr personal beliefs

  • Sets up huge difference across the country on kids who are vaccinated

• Can also be exempt for medical reasons

  • This all makes it hard to get to herd immunity number

Measles

• Isn't just a little rash

• Measles can be dangerous, especially for babies and young children

• Starts like flu and rash comes later – 3-5 days after symptoms begin

• About 1 in 4 people who get measles will be hospitalized

• 1 out of every 1,000 people with measles will develop brain swelling due to infection (encephalitis), which may lead to brain damage

• 1 or 2 out of a thousand die even with best care and health

• Airborne virus, transmitted by respiratory droplets

  • Small particle aerosols can stay suspended in air for long periods of time, and the virus can live on surfaces for up to 2 hours

  • Incubation period: contagious 10-12 days before symptoms

  • Virus infects 90% of unvaccinated people exposed to it

  • If you have vaccine your like 98% protected - very different

• Before 1963 when MMR vaccine became available: nearly all children got measles by 15 years old; 400-500 deaths, 48,000 hospitalizations

• The virus can remain dormant in the brain, eventually triggering chronic inflammation, brain tissue destruction and death 10 yrs later

• Eliminated in US in 2000, thanks to high MMR vaccination rates; now it’s back and raging

• Eliminated: in some parts of the world but not in parts its been eliminated

• Eradicated: wiped off face of planet (small pox only to be eradicated)

Measles vaccination rates pre and post pandemic

Significantly reduced post pandemic

How the federal government is failing to limit measles spread

• RFK Jr doesn’t think vaccinating is necessary 

 Smallpox

• a viral disease caused by variola, an orthopoxvirus

• The virus requires a human host; extremely contagious

• Infected individuals develop a systemic disease marked by extensive vesicular skin eruptions 

• Really high death rate

Smallpox History

• Smallpox erupted in periodic epidemics

• Mortality rates were 30% in adults, 90% in infants

  • ⅓ of survivors went blind

• Feared both for its high rate of mortality and life-long scarring of surviving individuals 

• In the early 1950s an estimated 50 million cases of smallpox occurred in the world each year → fell to 10-15 million by 1967 thanks to vaccination 

Smallpox Eradication Effort

• Endemic countries were supplied w/ vaccines

• Intensified effort was led in the 5 remaining countries in 1973

• By 1977, the last endemic case of smallpox was recorded in Somalia

• In May 1980, after two years of surveillance and searching, the World Health Assembly declared that smallpox was the first disease in history to have been eradicated

• Debate continues over whether strains of the disease should be kept in laboratories; threat of bioterrorism 

Smallpox was a particularly food candidate for eradication

1. Only human hosts (no animal vector)

2. Vaccinated humans develop a rapid and long-lasting immune response

3. The vaccine was inexpensive and easy to distribute and administer; there was no vaccine hesitancy

4. There is no ‘sub-clinical’ carrier state or infection 

   1. Can’t have disease and not show 

Challenges of Eradication

• Can be expensive

  • But long term, eradication is cheaper

• Hard to reach remote populations

  • Cultural differences, distrust of outsiders 

• Priorities of local populations vs. global public health

  • Focus on eradication takes away from other important health issues

  • Need to continue vaccine campaigns even when disease is eliminated locally

Polio (poliomyelitis)

• Polio is a highly infectious disease caused by the poliovirus

  • Affects the nervous system and can cause irreversible paralysis within hours

  • Mainly affects children <5 yrs old

• Transmission:

  • Can spread rapidly through a community, especially in situations of poor hygiene and sanitation

  • Enters the body through the mouth and multiplies in the intestine; then sheds into the environment through the feces 

Complicating factor of polio: Symptom-free carriers

• Most people infected with the poliovirus have no symptoms

• WHO considers a single confirmed case of polio paralysis to be an epidemic (could indicate thousands of carriers)

• Herd immunity is especially important 

Polio Global Eradication Initiative

• Polio can be eradicated

• Requires human host, can’t survive for long outside human body

• Cheap and effective vaccines are available to prevent polio

  • Oral polio vaccine (OPV) [and inactivated polio vaccine (IPV)]

  • OPV can be administered by anyone

  • One dose of OPV = 14 cents!

  • Long lasting immune response 

Polio vaccination campaign amid war in Gaza (2024)

• One case of a paralyzed child set off a massive campaign ot vaccinate all children <10 yrs old

• Health officials worked during humanitarian pauses to vaccinate and track carefully (because of constant population displacement)

• Vaccination came with Vitamin A distribution to boost immunity

Previous controversy surrounding polio vaccination in Pakistan

• 2011 - Fake vaccine drive to gather information about Osama Bin Laden’s location (Pakistani physician funded by the CIA)

• Consequences: hurt national polio campaign in Pakistan

  • Angry villagers chased off legitimate vaccinators, accusing them of being spies

  • Taliban banned polio vaccination teams

Guinea Worm Disease

- decreased from 3.5 million cases in 1986 to 542 cases in 2012 to 148 cases in 2013 to 126 cases in 2014

• Neglected tropical disease; parasitic infection caused by a nematode

• Contracted when people consume water from stagnant sources contaminated with Guinea worm larvae

  • Inside a human’s abdomen, larvae mate and female worms mature and grow

  • After 1 yr incubation, the female Guinea worm, 1 meter long, creates a lesion and slowly emerges from the body

  • Painful burning sensation; people seek relief by immersing their limbs in cool water sources; this stimulates the emerging worm to release its larvae and restarts the cycle of infection

• Incapacitates people for extended periods of time

Guinea Worm Eradication Campaign

• GWD could be the first disease to be eradicated using core public health practice: surveillance, case containment, and simple interventions (filter water, keep infected people out of water sources); without vaccines!

• It is biologically and technically possible to eradicate

  • Easily diagnosed because of its signs and symptoms

  • Worms emerge from the skin during certain predictable times of the year

• Only 6 African countries remaining to be certified as free of disease

• DALYs - Burden of Disease in a country (Malaria)

• Malaria is 4 on list for low-income countries but isn’t even on top 10 list of whole world

  • Really impacts low-income countries 

Malaria

• Malaria is caused by parasites (Plasmodium) that are transmitted to people through the bites of infected female Anopheles mosquitoes 

  • Can be infected multiple times throughout their lives

  • Malaria is preventable and curable 

• >198 million cases per year

• Death: >600,000 per year

• After fever onset, need to be treated within 24 hours to prevent death

• Billions of people at risk

•  population of target is kids under 5 ish?

Prevention of Malaria

• Individual level protection: long sleeves, bug spray, bed nets 

• Community level: spraying of insecticides 

• Community/societal level: vector control - decreasing risk of malaria by suppressing the mosquito population 

• Pharmaceuticals can also be used to prevent malaria

  • Chemophrophylaxis suppresses the blood stage of malaria infections, thereby preventing full blown malaria disease

    • Malaria pills for travelers

    • Preventive treatment of pregnant women in LMICs

Effectiveness of prevention modalities (malaria)

• When insecticide-treated bed nets are used properly by 75% of the people in a community

  • Malaria transmission is cut by 50%,

  • Child deaths are cut by 20%,

  • The mosquito population drops by as much as 90%

• Indoor residual spraying (IRS) with insecticides is the most powerful way to rapidly reduce malaria transmission

  • Most effective when at least 80% of houses in targeted areas are sprayed

  • Indoor spraying is effective for 3-6 months, defending on the insecticide used and the type of surface on which it is sprayed. DDT can be effective for 9-12 months in some cases

Diagnosis of Malaria

• Rapid diagnostic tests 

  • Drop of blood

• Important to be diagnosed so you can get on the right meds

Treatment of Malaria

• Ideally, confirm malaria infection using microscopy or rapid diagnosis test

  • Often diagnosed via symptoms

• Prompt treatment - within 24 hours of fever onset - with an effective and safe antimalarial is necessary to prevent life-threatening complications 

• Artemisinin-based combination therapies (ACTs) are recommended over older types of medications (chloroquine)

Malaria Vaccine

• RTS,S/Mosquirix vaccine was tested in a clinical trial in 7 African countries

• Approved by WHO in Oct 2021

• Vaccine roll-out in Ghana, Kenya, Malawi; 75-90% coverage for 1st dose

• Requires 4 doses

• Doesn’t completely prevent malaria, but lessens the anemia, hospitalizations, and mortality 

• Doesn't align with other vaccines kids need so families have to go to clinics more often etc. 

Elimination vs. eradication: Could we eradicate malaria?

• Things to consider:

  • Mosquito vector - hard to control

  • Not a perfect vaccine (yet)

  • Reinfection is common (not lasting immunity)

  • Can’t rely on symptomatic diagnosis - need ot increase testing

Evaluation of Public Health Interventions: using the RE-AIM Framework

1. Reach large numbers of people, especially those who can most benefit

2. Be effective

3. Be widely adopted in different settings

4. Be consistently implemented by staff members with moderate levels of training

5. Maintain replicable and long-lasting effects (and minimal negative impacts) at reasonable costs

TB: a top infectious disease killer

• TB is caused by bacteria & affects the lungs

• Airborne transmission: cough, sneeze, spit; only a few germs confers infection

• 10 million people fall ill with TB every year; 1.2 million deaths/yr; most occur in LMICs

• About a ¼ of the global population is estimated to have been infected with TB bacteria, but most people will not go on to develop TB

  • People infected with TB bacteria have a 5-10% lifetime risk of falling ill 

TB is preventable and curable

• In countries with high TB rates, the BCG vaccine is given to babies to prevent TB

• High risk for illness: babies and children, people who have diabetes, weakened immune system (ie, HIV/AIDS), are malnourished, use tobacco, COVID+

• Those who are infected but no yet ill with the disease cannot transmit it (latent TB)

• While TB primarily affects the lungs, it also affects the kidneys, brain, spine and skin

• TB disease is usually treated with antibiotics (4-6 months) but can be fatal without treatment

HIV/AIDS

• People estimated to be living with HIV in millions 

  • 37.9 million

• 1.3 million new people acquire HIV a year

• 39.9 live with HIV a year

• 630,000 dying a year with HIV

HIV Prevalence in US

• Approximately 1.1 million people in the U.S. are living with HIV today

• An estimated 38,000 Americans become newly infected with HIV annually 

• Men who have sex with men (MSM) bear the greatest burden by risk group, representing an estimated 26,000 of new HIV infections/yr

• 1 in 7 living with HIV are unaware of their infection

Who is greatest at risk of HIV/AIDS?

• Gay and bisexual men, infection drug users, sex workers, transgender individuals, black & Latino individuals

Transmission of HIV

• Routes of infection

  • Sexual

    • Homosexual or heterosexual

  • Percutaneous

    • Needle sharing

    • Accidental needle stick

  • Maternal-child 

    • Transplacental

    • Peripartum

    • Breast milk 

Primary target cells of HIV are Helper T-cells (CD4+

• These cells are really important for our immune systems

• HIV kills T-helper cells

• T Cells are one of the main controllers of the immune system → they detect pathogens and activate the immune system to fight it

• Without T Cells, a person’s immune system can’t fight off lots of diseases → AIDS

  • Opportunistic infections

    • Basically a lot die from other diseases due to weakened immune system

HIV → AIDS

• Less than 200 CD4+ T calls/cc of blood, compared with about 1,000 CD4+ T cells for healthy people

• Opportunistic infections and diseases

  • TB, bacterial pneumonia, toxoplasmosis (parasite), candidiasis (fungus)

  • HIV-associated cancers - Kaposi’s sarcoma, lymphoma and squamous cell carcinoma 

• Years without HIV medications turns into AIDS

• Important for HIV to be detected early so they can get meds to prevent AIDS

• Less talked about symptoms include mental health issues like anxiety, depression, stress induced insomnia 

HIV Testing

• Few unique signs or symptoms 

• Laboratory testing

  • Screening tests (antibodies)

  • Confirmatory tests (RNA)

• 15% of people living with HIV do not know their HIV status

• Transmission rate in undiagnosed people is 3.5x higher than in those who know their status

Advances in HIV/AIDS prevention

• Antiretroviral therapy

• Behavioral interventions:

  • Condoms, clean needle programs, HIV testing

  • Circumcision 

• Preexposure prophylaxis (PrEP) - prevents transmission from HIV+ sexual partner

• Postexposure prophylaxis (PEP) - taken within 72 hours of exposure to reduce risk of infection

Risk Factors for HIV Transmission

• Traditional risk factors

  • Biological 

  • Behavioral

  • Interpersonal

• Upstream determinants that affect tradition risk factors [Community/Societal levels of the SEM]

  • Community resources

  • Cultural norms

  • Inequality, racism, stigma

• → The most impactful interventions will address the upstream determinants of health! 

Structural violence and HIV

• Structural violence - a form of violence wherein some social structure or social institution may harm people by preventing them from meeting their basic needs

• Social Structures - economic, political, legal, religious, and cultural–that stop individuals, groups, and societies from reaching their full potential 

• Violence: causes injury to people (implies responsibility)

• Often almost invisible

• Society-level of the SEM; includes stigma

• Disparities in political power, educational attainment, healthcare, resources 

Structural violence

•  a form of violence wherein some social structure or social institution may harm people by preventing them from meeting their basic needs

Interventions & SMART Objectives

These objectives determine if an intervention improves health outcomes

• Each PH intervention/program is designed with specific goals in mind = SMART objectives!

• SMART objectives determine if the intervention is working or not

• If the intervention is not accomplishing its goals:

  • If it is not working well, fix it

  • If it does not work at all, try something else

  • Make sure it is not causing unexpected harm

• If the intervention is accomplishing its goals, celebrate it, publish it, scale it up, expand to other populations 

SMART Objectives

Specific

Measurable

Attainable

Relevant

Time Based

1. Define the goals of the intervention: WHO is going to do WHAT, WHEN, WHY, and TO WHAT STANDARD?

2. SMART objectives assess how well the intervention is working

TeachAids

• Culturally relevant, medically accurate videos, using famous icons to deliver AIDS prevention education  

• Research-driven 2D cartoon imagery provides the perfect balance of comfort and clarity for this highly stigmatized topic

• Collaboration with local NGOs for distribution 

How would you know if TeachAids is an effective intervention to combat HIV? Intervention example: TeachAids is rolled out at secondary schools in 5 communities in Kenya. Over 500 students learn about HIV prevention, safe sex, and HIV testing during a week-long program

• 80% of students can name 3 effective ways to engage in HIV prevention by the end of the week

• By the end of 2028, there is a 15% decrease in positive HIV cases in Kenya

• In a year, 60% of the 500 students will get HIV tested

• Over a year, we’ll see a 50% decrease in HIV in these communities, compared to communities with no intervention 

• AFter the 1 week program, 90% of secondary students in the 5 villages will be able to name 2 ways to keep themselves safe from contracting HIV

• After 5 years, the HIV transmission rate will drop by 30% in the 5 villages where the TeachAids program was implemented 

• In 1 year, 75% of the students who participated in the program will have procured condoms

Evaluating Partners in Health (PIH) accompaniment model for TB med compliance in Peru

• From the Bending Arc documentary: community health workers visited patients with MDR-TB 6x/week for 2 years to make sure they were taking all their meds 

• 2 SMART objectives that assess if the intervention worked: What outcome would you measure? How much of a change do you expect? Over what time period?

  • Measuring transmission rates

  • After 6 months of consistently taking medicine with community workers, are 50% of the patients still taking their medicine

  • By the end of the 2 years, 90% of community health workers will have visited their patients each day

  • By the end of the 2 years, 80% of patients were cured of TB