28. Infectious disease epidemiology Flashcards
what are infectious diseases?
a disease caused by an infectious agent and are transmitted through populations
how can infectious diseases be transmitted?
directly or indirectly via a vector
what can cause an infectious disease?
bacteria
viruses
fungi
protozoa
parasites
define endemic
a disease that is present permanently in a region or population
define epidemic
an outbreak of a disease that affects many people at one time and can spread through one or several communities
define pandemic
an epidemic that has become global
100 years ago what was the biggest cause of death?
infectious diseases
why has the infectious disease burden decreased?
vaccination
better nutrition
access to clean water
improved housing
what is the burden of disease?
the mortality plus the morbidity caused by the disease
how do we measure the burden of disease?
DALYs - disability adjusted life years
what is a DALY?
disability adjusted life year
1 DALY = one lost year of healthy life due to premature death or disease/disability
what proportion of DALYs are caused by infectious diseases?
17%
what does the UK health security agency do in terms of infectious diseases?
allocates the biggest proportion of its budget and staff to treat and prevent infectious diseases
what percentage of new infectious agents have originated from animals?
60-80%
what are the 2 steps in establishing an emerging infection in a new population?
- introduce the agent into the new host population
- establish and further dissemination of the agent within the new host population (called adoption)
what increases the risk of new emerging infections?
microbial adaptation
ecological changes
human factors
what microbial changes increase the risk of new emerging infections?
virus adapting to a new host /new species
antimicrobial resistance so not being able to treat infections
what ecological changes increase the risk of new emerging infections?
host environment in closer contact with humans
urbanisation
deforestation
climate change
globalisation
super commuters
what human factors increase the risk of new emerging infections?
changing demographics and behaviours
poverty
healthcare
global food industry
breakdown of public health measures
Susceptibility to infection
what are some major concerns with modern infectious diseases?
- Anti microbial resistance
- new highly pathogenic/virulent strains
- resurgence of disease due to lowered vaccination rates
- outbreaks threatening health, trade, security and economically important industries
- synergistic effects on the burden of non communicable diseases
why are infectious disease outbreaks also bad for non communicable diseases?
healthcare resources like doctors and medications are often taken away from their normal use or position to help deal with the outbreak leaving other patients not getting the care they need
define epidemiology
the study of distribution and causes of behaviours, health and disease in the population
what is the goal of epidemiology?
to understand that causes the disease and how we can control, prevent or treat them
about general health also like obesity
what is the descriptive mantra for epidemiology?
person, time, place
what are the 5 main questions epidemiologists are looking to answer?
- what disease or condition is present?
- who is ill?
- where do they live?
- when did they become ill?
- why did they become ill?
how do epidemiologists answer their questions?
with lots and lots of data
what does the data collected help epidemiologists identify?
- the health status of the population
- causation of the health problem
- evaluations of the interventions of the health problem
what are some questions we might ask when looking at causation?
is there an effect?
is this exposure protective?
does the exposure increase the risk of disease?
what is the magnitude of the effect?
what limitations do we need to consider when looking at causation?
- confounding causation - lots of effects that changes the relationship between the cause and the response
- reverse causation - does the outcome cause the exposure?
- measurement error
what is the hierarchy of evidence in epidemiology?
the higher up the list the more causation shown:
- randomised control trial
- cohort study
- case control study
- cross sectional study
what are cross sectional studies?
looking at a population at a set point in time
looking at the prevalence of disease not the causation
cases and controls
representative of the entire population
what are case control studies?
comparisons
take a history to retrospectively measure and compare the prevalence of exposure
not looking at causation
good for looking at rare outcomes
used to help identify risk factors and protective factors
what are cohort studies?
they follow a group of individuals for years eg children of the 90s or twin study
30 years + of data over different generations
can see the cause in the data and then see the outcome = causation
what are randomised control trials?
the gold standard of studies
2 randomised groups
the only difference between the groups is the intervention you are doing
observed the difference to see the effect
what is infectious disease epidemiology?
understanding how an infectious agent is transmitted and how it causes disease
what needs to happen in a time sensitive manner in infectious disease epidemiology?
- identifying infected individuals
- identifying exposed individuals
- control of the outbreak
in epidemiology what is measured using lab testing?
the infectious agent
what do epidemiologists look for in infectious agents?
- the natural reservoir
- the ability to survive out side the host
- ability to survive in unfavourable environments
- Adaptability
- how it is transmitted
what do epidemiologists look for in hosts?
how susceptible a person is using different markers
1. biological
2. Behavioural
3. social
4. Economic
what do epidemiologists look for in the environment ?
how much contact is occurring with the infectious agent
what kind of contact is occurring
what are the 2 horizontal modes of transmission?
direct and indirect
what is direct transmission?
touching secretions from another person
aerosol contact
skin contact
sexual contact
needle sharing
what is indirect transmission?
fomites
water
food
soil
vectors like mosquitoes and rats
what is vertical transmission?
through the placenta from the mother to child
what are the 3 main things to remember in infectious disease epidemiology?
- infectious diseases are infectious and transmit between hosts
- people can be immune
- preventive measure have scientific basis and have direct and indirect benefits
why is the incubation period important?
it can give you an idea of the type of pathogen
BUT you can be infectious before showing clinical disease
why do we use modelling of diseases?
to predict what will happen with different interventions
what used is in descriptive epidemiology?
person
time
place
how do we use person time place in infectious disease epidemiology?
who is affected by the disease?
- age, gender, behaviour, immunity
where is the disease clustered?
- workplace/country/climate
when is the disease occurring?
- seasonal or long term pattern
what is the incidence rate?
number of new cases / number of those at risk
at a set point in time
what is the attack rate?
number of new cases / number of those at risk
from the beginning to the end of the outbreak
what is the prevalence?
number of existing cases at that specified time / number of those at risk at that specified time
what is R0?
the basic reproductive rate
a measure of the intrinsic potential for an infectious agent to spread with no immunity/intervention
what is the R number ?
effective reproductive number
R = R0 x proportion susceptible
reflects real time transmissibility
varies depending on control measures
how is R0 calculated?
R = ßCD
ß = probability of transmission
C = rate partner acquisition - contact with disease
D = duration of infection
R0>1 = ?
spreading disease
R0=1?
Maintaining the disease
R0<1 =?
decline of the disease
infectious disease epidemiology:
example of ebola 2014-2016
direct transmission in bodily fluids
2-21 day incubation
fever, pain, headache, vomiting and diarrhoea
hospitalisation
R0 = 1.6-2.7
effective contact = barrier nursing and burial practises
number of contacts = isolate individuals early
duration = diagnostics and Surveillance
Intervention = isolation, safe burial, vaccine, monoclonal antibodies
what is public health Surveillance?
the systematic ongoing collection, analysis, interpretation and dissemination of health data
what does public health Surveillance do?
enables planning implementation and evaluation of public health programmes
what are notifiable infectious diseases?
a list of pathogens that must be reported if they are identified
why would a pathogen be on the notifiable infectious diseases list?
high mortality
high morbidity
pandemic potential
quick spread
not easy to contain
lack of effective intervention
what is the value of public health surveillance?
- identify outbreaks and guide disease control interventions
- inform vaccination strategies and vaccine formulation
- guide clinical management in the face of evolving anti microbial resistance
- guide allocation of resources
- detect and respond to emerging infections
when does an outbreak occur?
when there is more than the expected amount of disease in a population
what needs to be investigated in disease outbreaks?
How serious is the disease?
how infectious is the disease?
how preventable is the disease?
what are the 10 principles of infectious disease outbreaks?
- verify the accuracy of the disease reports
- Determine the existence of an outbreak
- establish a case definition
- identify additional cases
- conduct descriptive Epidemiology
- generate and test hypotheses
- monitor the course of the outbreak and reassess strategies
- carry out lab and environmental investigations
- Implement disease control measures
- communicate findings
what are some examples of immediate control measures?
Prophylaxis
isolation
public warning
hygienic measures
what are some outbreak control measures?
alert GPs and raise awareness of healthcare providers
educate the public
increase testing
control vectors (animals)
recall contaminated food measures
isolation and quarantine
Vaccination
what is active immunity?
infection
vaccination
what is passive immunity?
injections of antitoxins or Ig
maternal antibodies
what does herd immunity do?
protects the most vulnerable people and people that cannot be vaccinated
what does herd immunity refer to?
the proportion of a host population which is immune to an infection
what is disease control?
reduction of transmission risk to pre-defined levels
what is disease elimination?
reduction of transmission risk to near 0
what is disease eradication?
reduction of transmission risk to 0
(only happened with smallpox)
