#27 Epidemiology and Surveillance

Question 1

what is an Epidemic

What is a pandemic

what is endemic?

Answer 1

• epidemic is a sudden and severe outbreak in a group or population
• pandemic is a widespread epidemic affecting a whole region
• endemic is present in a population at all times at a low frequency

Question 2

what type of cross over does rabies have

what level is the disease at in the population?

Answer 2

rabies is only transmitted from animal to human
transmission of human to human cannot occur
therefore it is a sporadic infection of humans

Question 3

what type of cross over does Ebola have

what level is the disease at in the population?

Answer 3

ebola is transmitted from bat to monkey
monkey transmits to human
human to human transmission is possible
it is not endemic yet but may become endemic

Question 4

what type of cross over does Dengue have

what level is the disease at in the population?

Answer 4

dengue has an animal reservoir
it can be transmitted from animals to human via mosquito
effectively sustained in humans
therefore it is currently endemic in many places

Question 5

what type of cross over does HIV have

what level is the disease at in the population?

Answer 5

• cross over from primates to humans
• human to human transmission can occur and has been sustained in the populations
• is currently endemic but has been pandemic
  much easier for primates to pass a disease along because we are related

Question 6

explain endemic vs. epidemic

Answer 6

endemic is always circulating through a population - may be seasonal or affected by human activity. ongoing activity

epidemic occurs when the levels of an endemic go over a certain threshold - we get a threshold number from previous experience with the disease

Question 7

how does age incidence of disease determine how long immunity lasts?

Answer 7

• generally viruses that only infect the young will provoke lifelong immunity i.e. Measles
• viruses that can infect the old may provoke low levels of immunity - therefore you can get it multiple times throughout life i.e. Flu

Question 8

what are the key features for something to become pandemic?

Answer 8

novelty - needs to be new with little people immune to it
susceptibility - immune population is low. lots of people will be susceptible
transmissibility - needs to be transmissible between humans well

Question 9

what can we use epidemiological modelling for

Answer 9

to try predict outcomes

to understand previous infections

Question 10

what model is used for epidemiological modelling

what does it recognise

Answer 10

SIR model
considers susceptible population, infected population and recovered population

some people may become susceptible after they have recovered or immune

Question 11

what does the positive feedback loop in the SIR model recognise

Answer 11

• it recognises that there is a positive feedback loop between the infected people and incidence of disease
• the more people infected the more people they are going to infect
• if there is less people infected they are going to infected less people
  (the number of infectious people determines how may people will become infected)

Question 12

when will an epidemic start to lower

Answer 12

• when the pool of susceptible people has lowered

- when there are not many people to infect

Question 13

what are the host determinants of susceptibility?

give examples

Answer 13

age - young and old more susceptible
pregnancy - more at risk as they’re immunosuppressed
ethnicity - some genetics make people more susceptible
immune status - naive vs. vaccinated
underlying risk conditions - heart disease etc

Question 14

what are the virus determinants of natural history

Answer 14

• latency: harder to get rid of if its latent - more people you can infect the longer you are infected
• infectiousness: mode of transmission may make it easier to spread i.e. via coughing in comparison to sexual transmission. also if it can be infectious whilst asymptomatic
• immune response: may be strain specific or temporary

Question 15

what are some population determinants of viral spread

Answer 15

density of population
birth rate
household crowding
population mobility

Question 16

what are environmental risk determinants

Answer 16

sanitation
natural disasters
proximity to vector populations
proximity to animal reservoir populations

Question 17

What are surveillance approaches for pathogens?

Answer 17

disease surveillance data on government websites
syndromic surveillance 
serosurveillance 
crowd sourcing data 
social impact assessment 
household studies

Question 18

what is syndromic surveillance

Answer 18

where certain symptoms are recorded and monitored
syndromes such as diarrhoea and encephalitis
allows us to detect any unknown pathogens causing these syndromes and allows us to monitor any ‘out of the ordinary’ activity

Question 19

what information can be gathered from serosurveillance

Answer 19

• can detect how much of the population has been exposed to a certain pathogen
  including those that were asymptomatic

Question 20

what are generic interventions to any pathogen

Answer 20

environmental and personal hygeine
case contact and quarantine
personal protective equipment
social distancing

Question 21

what are specific interventions to a virus

Answer 21

pharmaceutical interventions
antiviral drugs
vaccines

Question 22

what does proportionate response mean

Answer 22

a response to a virus must be proportionate to the threat of the disease
just because something is pandemic doesnt mean its severe
you want society to go on

Question 23

how do you contain a virus

when do you do this

Answer 23

• this is a stringent measure
• extremely labor intensive
  only done when the virus has low transmissibility and high visibility - its a very severe virus
• containment as effects on the community and consequences

Question 24

how do you reduct transmission of a virus

when is this done

Answer 24

• this is done to slow down an epidemic
• reduces the height of the epidemic
• need to identify the key transmitters and target them to reduce transmission

Question 25

when do you use mitigation

Answer 25

when the virus cannot be contained
used to try reduce bad outcomes
identify the vulnerable groups to reduce their risk of bad outcomes such as death etc