W7 : Epidemiology

Question 1

Epidemiology is the study of?

Answer 1

the determinants (what), occurence (when) and distribution (how) of health and disease in a population.

Question 2

What is meant by “population at risk”?

Answer 2

A group of inidviduals who are susceptible to developing a particular disease or experiening a specific health event within a given time period.

Question 3

What is the ice berg phenomenon?

Answer 3

A situation in which a large percentage of a problem is subclinical, unreported, or hidden from view.

• Subclinical : disease that is suspected but is not sufficiently developed to produce definite signs and symptoms in the patient.

Question 5

What is the difference between an epidemic, endemic and a pandemic?

Answer 5

• Epidemic : Disease outbreak that is rapidly spreading in a limited region, and exceeds the baseline number of cases.
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• Endemic : Disease that occurs frequently within a geographical region. (at any given point in time, there will be infected people).
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• Pandemic :Disease that occurs with no restriction in geographical location.

Question 6

What is the difference between incidence and prevalence?

Answer 6

• Incidence : The number of new cases that occur in a specific population during a specific time period.
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• Prevalence : total number of disease cases (new + existing) in a specified population at a given point in time.

Question 7

What is the attack rate, and what is its equation?

Answer 7

Attack rate reflects the proportion of the population who become ill / infected after being exposed to the agent.
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Attack rate = (number of new cases / number of people exposed to the agent) * 100%

Note : just bc one is being exposed to agent causing the disease, doesn’t mean he/she will definitely fall sick !! Could be asymptomatic!!

Question 8

What is the difference between morbidity and mortality?

Answer 8

• Morbidity : the state of being ill.
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• Mortality : death

Question 9

What is an equation for morbidity rate?

Answer 9

(number of people with disease / total population at risk) * 100%

Question 10

What is a disease burden?

Answer 10

The impact of a health problem on a given population, which can be measured using a variety of indicators such as mortality, morbidity or financial cost.

Question 11

What is meant by surveillance ?

Answer 11

Systematic and ongoing collection, analysis, intepretation and dissemination of data for public health and food safety action.

Question 12

What are cohort studies? What is a metric used in cohort studies?

Answer 12

Cohort studies follow a group of people in time to see if they develop a certain disease
- Metric : relative risk

Question 13

What is a case-control study? What is a metric used in case control studies?

Answer 13

Case control studies is an observation study involving 2 groups : “case” (with disease) and “control” (without disease)
- Metric : odds ratio

Question 14

What is the difference between active and passive surveillance? Give an example.

Answer 14

Active surveillance : systematic / regular recording of events, often in a specific population / group of samples.
- e.g. government authroities reaching out to polyclinics to get reports of daily influenza cases

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Passive surveillance : Reporting of suspected events by stakeholders at their discretion.
- e.g. govt authorities do not reach out, just passively wait for doctors to submit monthly reports of influenza cases.

Question 15

When is active surveillance used?

Answer 15

It is often initiated when there is an outbreak of a (foodborne) disease in humans.

Question 16

What is the main disadvantage of active surveillance and what kind of bias is typically associated with it?

Answer 16

Disadvantage : active surveillance is very costly, especially when prevelance of disease is low.
- sampling bias

Over representation : prevalence or incidence of a disease may appear higher if the surveillance is focused on high-risk groups or regions.

Under representation : the disease burden in certain populations may be underestimated if they are excluded from the sampling process.

Question 17

What is the bias associated with passive surveillance?

Answer 17

Reporting bias.

There may be inconsistencies in reporting based on provider awareness, interest, or training. Some diseases may be overreported due to heightened awareness (e.g., during outbreaks), while others may be underreported due to a lack of training or diagnostic capacity. In addition, mild cases of foodborne illness may be underreported as patients may not seek medical care.

Question 18

What are some kinds of technologies used in laboratory surveillance?

Answer 18

RT-PCR / gene-based technologies / chemical foreinsic techniques

Question 18

Laboratory surveillance is always active surveillance. True or False?

Answer 18

False, laboratory surveillance can be active or passive.

Question 19

What is 1 advantage and 1 disadvantage of lab surveillance?

Answer 19

◡̈ High specificity and data quality

˙◠˙ High costs : reliance on samples and need for infrastructure and highly trained personnel

Question 20

What is syndromic surveillance? Give an example.

Answer 20

The use of non-specific indicators to detect food safety hazards, contamination events and illnesses.

• E.g. increase sales in loperamide (to help in diarrhoea) in pharmacies → some foodborne infection has occurred.

Question 21

What is 1 advantage and 1 disadvantage of syndromic surveillance?

Answer 21

◡̈ High sensitivity, but need to be combined with other surveillance to ensure high enough specificity.
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˙◠˙ Inability to distinguish between signals and background noise.
- e.g. looking at sales of loperamide (cures diarrhea) in pharmacies
- signals : those who buy loperamide bc they actually got the foodborne illness
- noise : people who have diarrhoea and buy loperamide, but not due to having foodborne illness.

Question 22

What is event-based surviellance ?

Answer 22

This is a system for quickly gathering information about food safety incidents from rumours or unstructured reports, rather than relying on routine data collection.

Question 23

For event based surveillance, where can information come from?

Answer 23

Sources such as news reports, health workers, food safety officials, non-govenmental organisations

Question 24

What is complaint based surveillance?

Answer 24

A system that collects information from anyone suffering from a food-borne disease that is attributed to a particular food establishment, food product, or event
- Includes complaints about malpractice and quality issues in food production or food safety, including physical contamination of foods.

Question 25

What is targetted surveillance?

Answer 25

Focus on sampling high risk populations / groups of samples.
- E.g. sampling of hamburger meat processed in large quantities, which is known to have higher risk of E.Coli O157 contamination than unprocessed meat.

Because processed beef is ground up and mixed, more chances for cross contamination ++ chance that it didnt get cooked properly (internal temp not reached) -> pathogens can multiply.

Vs unprocessed beef : whole cuts directly kept in chiller, which slows growth of microbes.

Question 26

What is sentinel surveillance?

Answer 26

Uses prearranged reporting sources (e.g., specific polyclinics) to monitor trends. Assumes the sentinel sample represents the total population.

• e.g. Sentinel was defined as polyclinics in the East. So, only sample from polyclinics in the East instead of all polyclinics in SG -> results generalised to the whole population

Question 27

When is sentinel surveillance useful?

Answer 27

Effective when resources are limited + monitoring common / frequent events

Question 28

What is risk based surveillance?

Answer 28

Surveillance that is guided by exposure and risk asessement info
- Only high risk foods are sampled. For example, for Listeria Monocytogenes (contaminated raw vege, animal meat, milk products), onlt sample cold cut meat / smoked salmon, which is high-risk

Question 29

What is participatory surveillance?

Answer 29

Involves directly engaging communities to report, monitor, and respond to health threats using local knowledge and priorities.
- Digital approach whereby individuals voluntarily monitor and report on their own health status through an app etc

Question 30

What is the main benefit of participatory surveillance?

Answer 30

It offers particular value that might not be possible to gather with traditional means like product sampling

Question 31

What is integrated surveillance?

Answer 31

Surveillance that combines data from humans, animals, food, and the environment to recognise how these systems are interconnected

Question 32

Integrated surveillance is often implemented under the ____ approach?

Answer 32

One health

The one health approach isaims to reduce animal and human health risks as a whole, with comprehensive environmental, ecological, social and economic factors in mind.