Lecture #31 - Outbreaks, Epidemics and Clusters

Question 1

1. Changing pattern of disease: epidemiological transition - what is it and how does it show the changing pattern of disease?
2. What is the change in burden of disease?

Answer 1

1. There are five stages - it follows the development of countries overtime and developed countries at approaching stage 5 when death > birth. Low income countries are at stage 3 or 4. Basically, stage 1 - pre transitional diseases because they’re infectious or have inadequate care. Once you start to get improved health, that death rate drop and population explosion. And then birth rates drop because contraceptives etc and population growth slows etc. Stage five, death > birth and natural decrease in pop
2. High income countries like NZ have most of their burden of disease being non-communicable diseases like CVD or diabetes or cancers. Middle income countries are still not as much and the low income countries have more than half their burden being communicable diseases (pre transitional) so it reflects the Epi transition. By 2030, expect even low income countries to have majority of their burden being from communicable diseases

Question 2

What is the One Health approach?

Answer 2

You consider the interaction of human health, animal health and environment. Since most are vector-borne diseases, this approach will become increasingly important.

Basically, Emerging and Reemerging infections - 70% of them are vector-born (mosquitos) or zoo tonic (come through animals)

Question 3

What 6 things influence the spread of disease

Answer 3

1. Properties of the agent (how virulent it is, how it’s transmitted, and ability for it to mutate). Age is the bacteria/virus that causes illness
2. Source of infection (where it comes from - soil, humans etc)
3. Biological reservoirs (some are found in animals that don’t harm the animal but the animals are reservoirs for the virus to spread to humans)
4. Host factors (are you immunosuppressed, malnourished etc)
5. Exposure variation (whether in closed e.g. plane or well-ventilated environment)
6. Environment - changing e.g. global warming - places that were too cold arena warm enough to keep vectors

Question 4

Epidemiological triangle:

1. What five 5 W’s do we look at when we do epidemiology stuff (outbreak investigation)?
2. What three things so we think about when we do epidemiolgy stuff in this field?
3. What three things are you generally looking at with the disease?

Answer 4

1. What (agent)
   - Who (person/pop)
   - Where (place)
   - When (time)
   - Why/how (causes, risk factors and models of transmission)
2. Host, Agent and Environment. So you do descriptive epi for host, lab investigation for agent (what bug is causing it?) and environmental investigation for environment (what are the conditions that lead to the disease e.g. water contamination)
3. Transmission (between host and agent) - how it spreads
   Survival (between agent and environment) - who survives
   -Immunity (between environment and host) - who becomes immune

Question 5

Infectious agents:

1. What are the 5 main ones?
2. What is the definition of infection and how is it different to infestation
3. What is the definition of infectivity?
4. Pathogenicity?
5. Virulence?

Answer 5

1. Bacteria, virus, fungi, protozoa, helminths (parasitic worms)
2. Infection = entry of a microbiological agent into a higher-order host and its multiplication within the host
   - Infestation is when the thing stays on the external surface like lice or scabies
3. Infectivity: ability of an organism to invade and multiply in a host (secondary attack rate) - if doesn’t invade and multiply, not gonna cause infection
4. Pathogenicity = ability of an organism to produce clinical symptoms and illness (proportion of those exposed who get ill)
5. Virulence = ability of an organism to produce serious disease (case-fatality rate)

Question 6

Transmission

1. What are the three ways agent can be transmitted?
2. What are the definitions of each?
3. Two terms under ‘indirect’ - what are they?

Answer 6

1. Direct, Indirect and Airborne
2. Direct = touching or inhaling infectious secretions (saliva, resp droplets, urine, faeces, other bodily builds)

Indirect = always involve a vehicle between host and agent

• inanimate = fomites (bedding, clothes, utensils); food or water; soil
• Live = vector (mosquitos, ticks)

Airborne = droplet nuclei - small particles less than 5 micrometers e.g. TB. So someone coughs, the droplets travel with the infectious agent and spread

Question 7

The infectious process

1. What needs to happen first?
2. What happens during incubation period?
3. What happens during clinical disease part?
4. What happens after recovery?
5. Where does the latent period start and go till?
6. What about incubation period?

Answer 7

1. You get exposed
2. Agent multiplies inside body
3. Get symptoms
4. You immune
5. Starts after exposure and lasts till just before symptoms appear (so you are infected but not yet able to spread disease).
6. The infectious period is like part way through incubation period (after latent ends) and you are able to spread the disease and this usually starts before you have full-blown symptoms (and symptoms can last beyond infectious period). So like, with cold - usually infectious before you get full symptoms but most infectious when fully ill with symptoms

Question 8

Do outbreak and epidemic mean the same thing?

Answer 8

Yes

Question 9

Outbreak/epidemic:

1. What is an outbreak/epidemic?
2. In other words, what is it?
3. How does that relate to epidemics?

4 & 5 - what really make it an outbreak?

Answer 9

1. Unexpected increase in the incidence of a disease
2. Occurrence of cases in excess of those expected
   - epidemic limited to a localised increase in incidence of disease
   - epidemic arising in an area that has no cases for a long time (or never had disease)
3. Two or more cases identified from a common course
4. Cases in excess of the expected number in a given time or place

Question 10

Endemic:

1. What is it?
2. Holoendemic = meaning?
3. Hyperendemic = meaning?

Answer 10

1. Constant presence of a disease or infectious agent within a geographical area or population group
   e. g. malaria is endemic to parts of Africa and Asia
2. Holoendemic = intense disease all year round children mainly infected, most adult immune
   - so ppl who have had the disease e.g. adult are gon’ be immune so burden of disease largely falls on children
3. Hyperendemic = intense disease with time periods of no transmission e.g. during some season - persistent disease with all ages infected (no one gets immune to it)

Question 11

What is pandemic?

Answer 11

Disease affected a large number of people and crosses many international borders

e.g. 1918 Spanish flu and 2009 swine flu

Question 12

Clusters:

1. What is it?
2. They’re usually…….
3. May have a…..

Answer 12

1. Aggregation of relatively uncommon events or diseases in space and/or in time that are thought to be greater than could be expected by change
2. They’re usually rare non-infectious diseases
3. May have a suspected environmental cause
   - often emerging diseases stat off as a report of a cluster

Question 13

Okay, I think this is the process of an outbreak - how many generations and include the terms primary case, index case and secondary attack rate in your description

Answer 13

• Start off with a completely non-immune population
• Generation 1 is where you have the first person infected - they’re known as the primary case (index case is the firs person recognised by health authorities that informs them of the occurrence of outbreak). Sometimes the primary and index case are the same but don’t have to be in like the case of ebola
• Then you get transmission or spread from initial case (SECONDARY RATE) - primary infected e.g. 7 people and this attack rate depends on infectivity, host factors, pathogenicity of agent etc in that flashcard 3
• Generation 2 is about how the 7 secondary cases go on to infect others but there is variable spread (some spread a lot and some don’t)
• Generation 3 is about people spreading again
• Generation 4 is about even more spread. But, as more people become immune (i.e. they’ve already had the disease), you decrease transmission so epidemic starts waning out
• Generation 5 is like where the epidemic peters out all together

Question 14

Epidemic curves:

1. What can they do?
2. Make this for what?
3. Represents number of…..
4. Why is it important to get as many cases?

Answer 14

1. They can describe what is happening
2. Make this for outbreak investigation
3. They represent number of cases per time (cases on y axis and generation on x axis i.e. time really)
4. Imp to get as many cases so we can get an idea about what cases you’re dealing with (what kind of outbreak it is?)

Question 15

Who recognises an outbreak?

Answer 15

Anyone can but depends on who is infected and how etc

But people like members of the community, media, clinicians etc. Even social media nowadays - they scan tweets and stuff and recognise outbreaks (barfblog)

Question 16

Why do we need to investigate outbreaks (6)

1. To stop…..
2. To prevent….
3. To address….
4. To reduce….
5. To identify…..
6. To identify……

Answer 16

1. To stop (the outbreak) and prevent further illness
2. To prevent further outbreaks from other similar sources
3. To address public concerns and involve the public in disease control
4. To reduce direct and indirect costs (if have lots of sick people, hospital costs go up_
5. To identify new mechanisms of transmission of known disease
6. To identify new or merging disease agents

Question 17

Outbreak investigation - what are the steps? (8)

Answer 17

1. Preparation - teams need to be ready at all time for a possible outbreak. They need to be ready to respond to reports etc
2. Surveillance - notifiable diseases etc to monitor these reports and send alerts to DHBs if increase in certain something
3. Confirmation
4. Outbreak description
5. Outbreak investigation (analytic epi component, enviromental component and lab component)

Question 18

3. Outbreak confirmation:

1. What is this about>

Answer 18

You need to confirm it’s actually an outbreak. An increase in number of cases may just be a seasonal trend when you put it in context of wider info

Question 19

4. Describing outbreaks
5. What three things to consider?
6. What are the 3 types of outbreaks?
7. What do the graphs look like for that?

Answer 19

1. Consider person (who), place (where) and time (when)
2. Common source - point source (e.g. common event - at a function; everyone at the uncooked chicken and got exposed so same time and place) , continuous common source (same place bit prolonged overtime e.g. contaminated H2O supply) or intermittent source (e.g. water supply only infected after bad rainfall)
   - Propagated source (person to person) like HH/institutional (e.g. freshers flu at hall)
   - Mixed e.g. point source then propagated person to person (e.g. agent for diarrhoea comes from food but then spreads person to person)
3. For common source - like a bell curve

For continuous = like a rectangle (outbreak but maybe not recognised or dealt with so increase in cases and it keeps increasing until large number of people affected)

For intermittent = little blips throughout. First people infected and then it dies away and then another lot and then another lot

For propagated source (person to person) = it’s like small and then gets big. People just keep infecting each other.

Question 20

Go read the examples on your own

Answer 20

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Question 21

What is the difference between a point source outbreak and a propagated (person-to-person) outbreak?

Answer 21

A point-source/common-source outbreak occurs when many people are suddenly exposed to the same source of infection, such as a contaminated water supply or contaminated food at an event.
In contrast, a propagated outbreak occurs when an infection is introduced to a susceptible population with subsequent transmission from person to person and a progressive increase in incidence.

Question 22

Describe the steps in an outbreak investigation.

Answer 22

• Provisional case definition
• Confirm that the epidemic exists
• Assess the extent of the outbreak and its essential epidemiological features
• Define the population ‘at risk’ (the denominator)
• Formulate working hypotheses
• Test the hypothesis
• Control the outbreak
• Report and communicate the findings from the investigation

Question 23

Describe the information an epidemic curve can provide outbreak investigators.

Answer 23

Incubation period – the time from exposure to onset of symptoms
Distribution of cases over time, which will help determine whether transmission is person-to-person or point-source.