Lecture 27 - Epidemiology and Surveillance of Viral Infections

Question 1

Definition of sporadic outbreaks

Answer 1

Occasional cases of a viral infection

Question 2

Definition of endemic

Answer 2

Present in the community at all times, but at a relatively low frequency

Question 3

Definition of an epidemic

Answer 3

A sudden, severe outbreak in a region or group

Question 4

Stage 1 crossover event

Answer 4

Only transmitted between animals

Question 5

Stage 2 crossover event

Answer 5

Only transferred from infected animal to a human (EG: rabies)

Question 6

Stage 3 crossover event

Answer 6

Limited outbreak. From animal reservoir to humans, with some low-level human-human transmission (EG: ebola)

Question 7

Stage 4 crossover event

Answer 7

Long outbreak. From animals to humans, with many cycles of human-human infection (EG: Dengue)

Question 8

Stage 5 crossover event

Answer 8

Only human-human transmission

Question 9

Example of an endemic virus

Answer 9

HSV

Question 10

Difference in epidemiology of diseases that affect different age groups

Answer 10

Diseases that give lifelong immunity often are diseases of the young

Diseases that only give partial immunity often have a more even age distribution

Question 11

Factors leading to a pandemic
1)
2)
3)

Answer 11

1) Novelty
2) Susceptibility (if healthy adults are over-represented among the sick or dead)
3) Transmissibility

Question 12

Factors involved in epidemiological modelling
1)
2)
3)

Answer 12

1) Explicitly considers the causal processes involved in infection and transmission
2) Recognises interdependence of factors
3) Means of synthesising data from basic science and population studies

Question 13

SIR paradigm

Answer 13

Susceptible->infectious->recovered

Infectious infects susceptible based on ‘beta’ coefficient (measure of innate infectiousness of virus)

Question 14

Example of a population at particular risk of viral infection

Answer 14

Indigenous Australians have a restricted T cell repertoire against influenza

Question 15

Host determinants of susceptibility 
1)
2)
3)
4)
5)

Answer 15

1) Age
2) Underlying conditions
3) Immune status
4) Pregnancy
5) Race

Question 16

Virus determinants of natural history
1)
2)
3)

Answer 16

1) Latency
2) Infectiousness (pre/asymptomatic, duration of infectiousness, mode of transmission)
3) Induction of immune response (temporary, strain specific or not)

Question 17

Population determinants of spread
1)
2)
3)
4)
5)

Answer 17

1) Birth rate
2) Household size
3) Social and employment networks
4) Population density and connectedness
5) Population mobility

Question 18

Environmental determinants of spread
1)
2)
3)
4)
5)

Answer 18

1) Seasonality
2) Sanitation
3) Proximity to vector populations
4) Proximity to reservoir animal populations
5) Natural disasters

Question 19

New method of disease surveillance

Answer 19

Symptom surveillance

Question 20

Symptom surveillance

Answer 20

Identify specific sets of symptoms, rather than particular diseases.
Reliant on clinicians reporting out-of-the-ordinary symptoms

Question 21

Advantages of symptom surveillance
1)
2)
3)

Answer 21

1) Not restricted by individual disease diagnosis
2) Year-on-year disease burden measured, out of the ordinary disease activity is detected.
3) Uses threshold detection algorithms to detect such spikes in incidence.

Question 22

Method of disease surveillance that can detect symptomatic and asymptomatic infection

Answer 22

Serosurveillance

Question 23

Social impact assessment example

Answer 23

See if number of days of work missed increases over a certain period, and if this correlates with what might be an epidemic

Question 24

Type of study that can identify less-serious infections

Answer 24

Household studies. Hospitalisations only represent the most-severe cases

Question 25

Intervention endgames
1)
2)
3)

Answer 25

1) Containment
2) Transmission reduction
3) Mitigation

Question 26

Importance of infection mitigation

Answer 26

Reduce burden on public health system

Question 27

Why is it hard to identify initial infection source of ebola?

Answer 27

Incubation period is 2-21 days.

Question 28

Ebola patient zero

Answer 28

Thought to be a 2 year old boy, infected mother, sister, grandmother.

Question 29

When is containment of a virus feasible?

Answer 29

When virus has low transmissibility, high visibility.

When labour is available (very labour-intensive)

Question 30

Effect of transmission reduction
1)
2)
3)

Answer 30

1) Slows down epidemic
2) Can buy time for effective intervention
3) Reduces peak burden on healthcare system, but can prolong time of burden