38 Epidemiology and Population Health Flashcards
What are the three key elements required in an infection cycle?
- An infectious source (pathogen)
- Susceptible host(s)
- Spread to more hosts
What is the route of transmission for enveloped viruses?
Enveloped viruses (e.g. Covid-19)
1. The outermost envelope is made up of phospholipids, proteins or glycoprotein which surround the capsid
2. Enveloped viruses are less virulent, often released by budding and rarely cause host cell lysis
3. Are sensitive to heat, acids, and drying
4. Generally cannot survive inside gastrointestinal tract
5. Lose infectivity on drying
6. Will induce both cell mediated and antibody mediated immune response in the host
7. Mode of transmission is through blood or organ transplants or through secretions
What is the route of transmission for non-enveloped viruses?
Non-enveloped viruses (e.g. Polio)
1. The outermost covering is the capsid made up of proteins
2. Non enveloped viruses are more virulent and causes host cell lysis
3. These viruses are resistant to heat, acids, and drying
4. It can survive inside gastrointestinal tract
5. It can retain its infectivity even after drying
6. It will induce antibody production in the host
7. Mode of transmission is through fecal or oral matter and dust (most likely)
What is the incubation period?
Time between catching an infection and symptoms appearing.
What is the infectious period?
The time period in which the infected person is able to transmit the disease to a susceptible host/vector. Not necessarily associated with symptoms.
What is the latent period?
time between catching an infection and diagnostic signs of an infection (immune response) but still asymptomatic.
What is the definition of a pandemic?
An epidemic that is now occurring worldwide, or over a very wide area, crossing international boundaries and affecting a large number of people
What is the definition of an epidemic?
A wide-ranging spread of disease throughout an entire area or particular community (can grow to be national)
What is the definition of an outbreak (of an infection)?
When 2 or more people experience a similar illness and are linked by time or place
(smallest scale of notable disease spread)
What are the measures of transmissibility?
Attack rate and secondary attack rate.
What is attack rate?
The proportion of people becoming infected in a population initially free from the disease
What is secondary attack rate?
The proportion of people becoming infected among contacts of people with the disease
What are the different methods in epidemiology?
Case control studies, cohort studies, randomised controlled trials.
What are cohort studies?
*An observational, prospective research study.
*A type of epidemiological study in which a group of people with a common characteristic is followed over time to find how many reach a certain health outcome of interest.
What are RCTs?
*A study in which there are at least two different treatment groups. The people taking part are put into one of the groups at random.
- to overcome sources of bias
*Can be placebo controlled
*Experimental + interventional
What are case-control studies?
*Retrospective
*A type of observational study commonly used to look at factors associated with diseases or outcomes. Researchers start with ‘cases’ of disease and then find ‘controls’ (without disease) and compare them.
What is the aim of a Phase I clinical trial?
initially evaluating the safety + immunogenicity (ability to stimulate immune response) in a small population
*N ~ 1-100. Vaccine safety + tolerability evaluated over different dosages/ regimes.
What is the aim of a phase 2 clinical trial?
expanding to a larger/ more targeted population
*To obtain safety + immunogenicity data to support a larger subsequent efficacy study
*N ~ 100 - 500. Allow for more accurate characterisation of safety + immunogenicity
What is the aim of a phase 3 clinical trial?
randomised clinical trial comparing new treatment against the standard treatment
*N ~ 1000 - 100,000. To evaluate efficacy of new treatment in population of interest
*In these studies, participants are randomly allocated the new treatment or control (alternative treatment/ placebo)
*Double blind to prevent bias
What is the aim of phase 4 clinical trials?
Carried out after the drug has been licensed.
Used to find out more about long term risks and benefits.
What are socio-economic factors that place people at higher risk of developing TB?
- Poor living conditions
- Homelessness
- Incarceration
- Poverty
- Tobacco use
- Alcohol abuse
What are some risk factors for contracting HIV?
- Unprotected anal/vaginal sex
- Having another STI
- Sharing contaminated needles
What are some risk factors for getting malaria?
- Living in/travelling to a region where malaria is present (biggest risk factor) - near water, hot, etc
- Not protecting yourself from mosquitoes (with nets/coils etc)
- Poor housing
What is a nosocomial infection?
An infection acquired in hospital
What is are two examples of nosocomial infections?
MRSA infection
Norovirus infection
What is an iatrogenic infection?
An infection caused by treatment or diagnostic procedures
What is an example of an iatrogenic infection?
C. difficile infection
What is the impact of immunisation on morbidity and mortality?
Significantly decreases morbidity and mortality
What are the two main aims of vaccinations?
1) Protect that person against unpleasant/fatal infections
2) Make that person unable to pass the pathogen to someone else, benefitting the whole population (herd immunity)
What are examples of challenges in vaccine development?
General:
- Extremely high safety standards
- Complex development, formulation and manufacturing
Pathogenic:
- High antigenic variation
- Immune evasion
- Immune destruction
- Complex life cycles
What are the characteristics that make a good vaccine?
- Safe
- Highly effective
- Cost-effective
- High thermal stability
- Multivalent
- Creates long-term immunity
What is vaccine efficacy?
How effectively a vaccine reduces infection
= The comparison of disease rate between vaccinated and unvaccinated people
e.g. 80% reduction = 80% efficacy
What is known to be the first vaccine, and by who?
Smallpox vaccine (which was the vaccinia virus aka cowpox) by Jenner
When was the MMR vaccine introduced?
1969
Which type of polio vaccine did Salk and Sabin each create?
Salk: inactivated
Sabin: live attenuated oral
What was the old vaccine development approach?
Empirical
Directly making the pathogen weaker and injecting it to form an immune response
What is the current common vaccine development approach?
Genomic
Sequence pathogen genome, then decide target gene
Use various methods to make vaccines (recombinant, subunit, RNA, etc)
What is the significance of vaccine side effects?
- They cause ‘disease’ in an otherwise healthy individual
- They must be considered in a risk-benefit analysis of whether individual risk is worth it for the population benefit
How is the effectiveness of a vaccine determined?
Randomised controlled trials, either against current available options or a placebo.
What is the difference between prophylaxis and immunisation?
Prophylaxis = general measures taken for disease prevention e.g. rapid tests, prophylactic antibiotics
Immunisation = specific protection against a particular disease
What are the leading causes of infant and childhood mortality and morbidity in resource-limited health care systems?
Vaccine-preventable diseases and infections due to resistant pathogens.
*e.g. AMR in Streptococcus, pneumonia, malaria
Why is infection a leading cause of death in developing countries?
- Poor education
- Low health knowledge
- Poor infrastructure
- Environmental factors (e.g. access to clean water)
- Lack of nutrients
Why is there a higher rate of antimicrobial resistance in developing countries?
- Lower vaccine uptake due to lack of funding/poor education etc
- When people are infected, need to be prescribed more medications to manage disease
- Contributes to emergence of resistance
What are the main public health measures for the prevention and control of communicable disease?
- Surveillance
- Prophylaxis
- Treatment
- Immunisation
- Public education
What is a ‘notifiable disease’?
Any disease that is required by law to be reported to government authorities
Give any examples of ‘notifiable diseases’ in the UK
Acute encephalitis, cholera, COVID-19, food poisoning, malaria, leprosy, measles, tuberculosis, yellow fever
What is herd immunity?
A population shows herd immunity if the frequency of
immune, non-susceptible people is high enough to break the chain of transmission.
What is the critical vaccination percentage?
The percentage of the population that must be vaccinated to reach the herd immunity threshold
What is the basic reproductive rate, R0?
R0 = the average number of of persons infected
by one disease source
*If R0 < 1, the disease will eventually disappear
*If R0 > 1, the disease will continue to spread
What is the equation for R0?
R0 = C x P x D
*C: the number of contacts an infected person makes per unit time
*P: the probability of transmission per contact
*D: the duration the infected person is infectious to others
What are three measures that can be used to reduce the R rate?
- Treatment –> shorten infective period
- Change behaviour (face masks, isolation)
- Prophylaxis (only in advance though)
What are the different ways in which transmission of an infectious disease can be reduced?
- Physical isolation
– Quarantine, to give enough time for an infection in a
host to manifest itself without being allowed to
infect others
– Barriers - e.g. during sex, against Sexually Transmitted
Diseases (STDs) - Control of vectors and reservoirs (e.g.
Malaria) - Prophylactic immunisation - vaccination
- Clean air, water, food
- Education
What are examples of continuous variables in epidemiology?
- T-cell count
- Duration of a symptom
- Infant mortality rate
What are examples of discrete variables in epidemiology?
- Blood type
- Number of ill people exposed to a risk factor
What are examples of independent variables in epidemiology?
- Individual age
- Population size
- Use of a drug
- Vaccine uptake
What are examples of the dependent variable in epidemiology?
- Rate of infection
- Severity of symptoms
- Mortality rate
What is the definition of a dependent variable?
An output variable that is observed and has a value that depends on the indepdendent variable
What are the two main statistical tests used for comparing two proportions?
- Z-tests
- Chi-squared tests
What does the Chi-squared test measure?
If there is a significant relationship between two variables from the data
What does the z-test measure?
Whether there is a significant difference between the two population means
What does a confidence interval refer to?
The range of data within which you can be 95% confident that the true value/mean lies within
What is a hypothesis test?
A test of statistical significance for comparing two proportions
What are odds?
the probability of an event occurring, divided by the probability of the event not occurring
What is the odds ration?
The odds ratio is used for the analysis of case-control studies
