Epidemiology & Surveillance Flashcards
What is an emerging infection?
infections that have newly appeared in a population, or have previously existed but are rapidly increasing in incidence or geographic range
Focus of a PH professional for CDC
- Contacts
- Source
- Prevention
- Control
What is an epidemiologic transition
phenomenon whereby the prevalence and type of disease experienced by a country evolves with development. Over time (development), prevalence of infectious diseases falls and that of non communicable diseases increases
What country characteristics increase infectious diseases
- low wealth
- low development
Why are IDs more common in less developed settings (5)
lack of safe drinking water
poor sanitation
overcrowded living conditions
limited access to healthcare
malnutrition
What are the negative effects of urbanization (5)
Pollution
Accidents
Heat Island effects
Climate change
High population density –> ID outbreaks (particularly in overcrowding and poor WASH)
What is the effect of globalisation & global trade?
economic linkages & dependencies between countries –> greater movement of peoples, goods & services.
Global trade –> environmental degredation & climate change
Benefits of globalization to ID
growth of communications technology
social networking
research links
spread of healthcare technology
–>enable health knowledge & expertise to be widely disseminated
Effects of technological advances & travel
air travel –> rapid ID spread.
Import of diseases from endemic countries to non endemic countries
Health tourism - spread both ways
transport of disease vectors & pathogens
food born diseases
Effect of healthcare advances
Invasive medicine - creates means for infection to be introduced - including opportunistic.
Antibiotic resistance - increasing concerns especially with spread due to travel
Effect of climate change
increased suitable breeding environments for mosquitos & accelerate their lifecycle –> increasing numbers
–> increase in infectious diseases e.g. Malaria & Dengue
Extend breeding habitat for ticks
Increase in extreme weather events –> further ID outbreaks
International initiatives for ICD control
GAVI; WHO Essential Medicines list
etc
International health regulations: notifiable diseases, health rules for trade and travel, measures for disinfecting ships etc, health documents required
What is a PHEIC (public health emergency of international concern)
an extraordinary event which is determined to constitute a public health risk to other States through the international spread of disease and potentially require a coordinated international response
Early Warning Systems
EnterNet (enteric pathogens)
EARSNet (antimicrobial resistance)
EISN (influenza)
GOARN - WHO global outbreak alert and response network
What is ‘One Health’
broader focus looking at people, animals, plants and the shared environment as they all interlink – therefore multisectoral approach to health
What is the purpose of epidemiology
to identify risk factors & trends in infection
What to look for in terms of distribution of disease
Time
Place (geographical link, setting)
Person (contacts of index case & anything specific about the people getting it)
What do communicable disease interventions target
Anything along the lifecycle of disease:
source, pathway, receptors
Reservoir –> agent –> host –> reservoir
What is a vehicle
a vector that isn’t a living thing. E.g. needle, surgical equipment
How to describe disease
Frequency (how often occuring)
distribution (time, place, person)
Determinants (are there common factors e.g. smoking, social deprivation, occupation)
Describe the chain of infection
reservoir –> portal of exit –> agent –> mode of transmission –> portal of entry –> host –> person to person spread –> reservoir
Features of Direct transmission
Direct contact with infected material or pathogens
e.g. scabies, viral gastroenteritis
Includes fomites
Can have multiple modes of transmission e.g. respiratory diseases -> airborne and direct by droplets settling onto objects
Indirect transmission
Vector borne or vehicle borne
Endemic def
Persistent level of disease occurrence
Hyper-endemic
persistently high levels of diseases occurrence
Sporadic
Irregular pattern of occurance
Epidemic
Occurrence in an area in excess of what is expected for a given time period
Pandemic
Epidemic widespread over several countries
Outbreak
2 or more cases of a disease that are linked
OR
occurrence of a disease (can be just 1 case) that is not expected in an area e.g. Ebola in UK
If cases aren’t linked (and not unexpected disease) its not an outbreak its a cluster
Common source outbreak
When a group of persons have been exposed to a common source of an infectious agent or toxin. e.g. at the same restaurant
Point source outbreak
When the exposure to an infectious agent or toxin has occurred over a brief period of time
Propagated Outbreak
When an outbreak is gradually spreading from person to person.
Epidemic curve is initially separate waves and then they start to merge together as incubation periods etc. start to overlap
How to describe an epidemic curve
describe background level of infection (what level for how long)
Describe increase at what week and to what level
Then describe if there is a decline after that
What does the incubation period encompass on natural history of an ID
Latent period = point in time where person acquires the infection until the point they become infectious.
AND
Asymptomatic infectious period
Then when symptoms develop incubation period stops
Infectious period
Includes when asymptomatic but infectious and when symptomatic
What happens in disease
organ/tissue damage (not the same as symptoms
What is the secondary case also
a primary contact of the index case
What is infectious dose
quantity of microorganisms needed to produce infection in the host
What is infectivity
proportion of exposed persons who become infected
aka attack rate
What is pathogenicityk
proportion of infected persons that develop the disease
What is virulence
the proportion of persons who develop the disease who become severely ill or die
what is disease incidence
number of NEW cases occurring over a given time period in a defined population at risk (that are disease free initially)
What is incidence rate
the number of new cases of a disease divided by the number of persons at risk for the disease. (in a certain time period)
What is disease prevalence
Number of EXISTING cases at a given point in time in a defined population
Point prevalence (point in time) vs Period prevalence (over a time period).
If prevalence is dropping its because people are dying
What are attack rates
proportion exposed that get ill?
Case fatality rates
Proportion of cases who die from it
Odds
measure of the likelihood of one event occurring compared to another event
odds = number of event A occurring/number of event B occurring
event A normally = cases of disease. event B normally = number of those who don’t get it
Odds Ratio
Odds ratio: This is ratio of one set of odds against another. Odds ratios are frequently
calculated from case-control studies where we compare the experience of CASES (e.g.
persons with disease) against CONTROLS (persons without disease).
Vaccine efficacy
protective effect of a vaccine
reduction in disease incidence among people who have been vaccinated compared to disease incidence in those unvaccinated
What are the steps of the surveillance process (6)?
- Planning and system design
- data collection
- data analysis
- interpretation of results of analysis
- dissemination & communication of information
- application of information to public health programs and practice
Issues/barriers in surveillance
incomplete data
non standardised data
overlapping/changing categories
loss of data
duplication of data (multiple recording systems)
not incentivised
not comparable e.g. cases of covid between countries due to different testing etc
What is a case definition in surveillance
what criteria would you use to define a case
Clinical criteria vs microbiological criteria
Not the same as a diagnosis
Examples of data sources in surveillance
reports from clinicians
lab reports
screening
primary care reporting e.g. sentinel GPs
Death certification
surveillance units e.g. British paediatric surveillance unit
enhanced surveillance (e.g. TB, meningitis)
International surveillance
What is the purpose of surveillance
Detection of any changes in a disease
Track changes in disease
Detection of new diseases
monitoring and evaluation of prevention & control measures
to aid prioritisation decisions
How to explain surveillance data
need to look at trends because the actual numbers are unreliable because:
only a proxy measure - not every case detected/reported
Spurious/artificial - failing to notify, notifying wrong
changes in diagnostic methods
changes in attention of the observer
change in observer
random variation
Is it a true outbreak? Or is it seasonal variation etc.
Types of surveillance systems
Passive
Active
Enhanced
Sentinel
what is passive surveillance
most surveillance systems
e.g. routine lab/clinician notifications of disease to a surveillance center
surveillor doesnt do anything - the data comes to them
degree of incompleteness
often get very little information about the case
What is active surveillance
used in situations where complete reporting is required
requires negative reporting also
e.g. for serious/highly contagious disease; monitoring of vaccine failure etc.
Expensive & time consuming - have to contact hospitals/clinicians to ask about cases etc.
Usually only done over a short period of time
What is enhanced surveillance
Form of active surveillance (but less active)
usually limited to a specific area, time period and disease type for a specific purpose. Health units are required to report cases of diseases that would not normally be routinely monitored.
Often provide incentives
What is sentinel Surveillance
Incentivise some sentinel sites to report information – e.g. some GP practices etc. extrapolate from those clinics. Works best for common diseases - more likely to miss rarer conditions
What can surveillance be of
disease
determinants of disease
animal and bird reservoirs
What are complex adaptive systems?
System of thinking where you can’t understand the system by looking at individual actors - sees healthcare as a dynamic process
What are the 3 core characteristics of a complex adaptive system
Heterogeneity, interact —> emergence
- heterogenous agents (e.g. people, organisations, pathogens, animals etc.)
- agents interact with each other and evolve their behaviour over time
- interactions lead to a pattern called emergence - where the network of actors behave in difficult to understand ways.
Emergence disguises cause and effect in positive and negative ways.
e.g. ant colonies
Integrated Disease Surveillance and Response
aims to integrate multiple categorical surveillance and response systems - linking surveillance, laboratory & other data with public health action.
Example: WHO/AFRO IDSR guidelines combine event based & indicator based framework with disease priority framework and one health approach to zoonotic/vector born disease
Event based surveillance
detect outbreaks, using official and unofficial reports, need to verify reports meet specific case definition (most credible when supported with labs).
Can be reported early, even before been to Dr (because informal); can be used anywhere; used for all PH events involving potential disease including with unknown cause
Indicator based surveillance
detects outbreaks, define disease trends, seasonality, burden, risk factors
Reports of cases from health providers (drs, labs etc.). –> usually credible as HCPs told to only report those that meet case definition (but most credible supported by lab).
Timescale: reported after patient has sought medical attention (so can be delayed); only used where there is healthcare infrastructure & willing HCPs; usually only used for known diseases
IDSR Framework categories of diseases based on priority for surveillance
- Epidemic-prone diseases/conditions/events that require immediate reporting (can be passive or active) - case-based identification using standard case definitions for high-priority diseases. e.g. acute haemorrhagic fever syndrome, anthrax, bacterial meningitis, cholera etc.
- Diseases targeted for eradication or elimination (may be part of case based strategies or may have dedicated eradication programmes) e.g. Buruli ulcer, bacterial meningitis, leprosy, malaria, measles
- Other major diseases/events/conditions of PH importance e.g. HIV, TB, Malaria, viral hepatitis, adverse events following immunisation
Why do you get significant osscilation in incidence over time
population wide immunity - after 1 wave people either die or become immune, then as a few years pass you get new population (e.g. babies, migrants) and loss of immunity - so then you get another spike (cyclical pattern of infection)
Reasons for poor vaccine uptake
Mistrust of authority (particularly within minority groups)
Misinformation
Lack of scientific literacy
What is an epidemic threshold line used for
e.g. to authorise use of antivirals for influenza - outside of flu season you can’t use antivirals (economic and clinical reasons - outside of flu season/epidemic levels it is unlikely that it actually flu over another virus)
What is cryptosporidium and what does it cause
intracellular parasite - biggest cause of non viral diarrhoea
Typical age of incidence of cyptosporidium
peak age of incidence: 1-5y
marked reduction over 35y
Transmission & Risk Groups for Cryptosporidium
Faeco-oral transmission
- Person-person spread
nurseries, food handlers, animal contact, MSM.
Occupational: vets, animal handlers, farm workers
Common in lamb & calf diarrhoea - transmitted in surface run off water - so incidence can be seasonal and related to rainfall
Waterborne transmission:
- oocysts are resistant to chlorination & many disinfectants - unboiled tapwater, swimming pools
Cryptosporidium reservoir for infection
GI tract of animals & humans
Clinical manifestation of cryptosporidium
Self limiting in most, chronic in immunodeficient & AIDS.
Low infectious dose
Symptoms: watery diarrhoea lasting 2-4 days, abdominal cramps, fever, vomiting, anorexia.
Likelihood of recurrence: autoinfection
Management of cryptosporidium cases
Enteric precautions (hand washing, don’t use alcohol hand rub, hygiene etc., gown and glove)
Safe disposal of faeces
Exclusion until 48 hours after first normal stool
Avoid using swimming pools for 2 weeks after first normal stool
Immunocompromised should boil drinking water
What to do if water standard breached (cryptosporidium)
Info: when & where was sample; no. of oocysts per 10L, results of viability testing; source of the affected water; how was water treated; distribution area of water supply; any problems with water supply; any recent changes in treatment/source of water; how fast does water travel through distribution area; history of sampling/previous outbreaks
Options for action:
1. take no action
2. Convene incident management team: give advice to special groups, enhanced surveillance for human cases, request alternative source of water, boil water notice
Examples of international surveillance
Morbidity & Mortality Report (CDC)
Global Networks e.g. GOARN
International collaborations: EISS (european influenza surveillance scheme), EU-IBIS (EU Invasive Bacterial Infections Surveillance), Enter-net, Pro-MED (programme for monitoring emerging diseases)
International Health Regulations
Updated in 2005.
WHO member states are required to notify WHO for certain diseases.
Health related rules for international trade and travel
Health organisation: measures for deratting, disinfecting, disinsecting ships etc.
What are the IHR notifiable diseases
Always notifiable: small pox; poliomyelitis due to wild type poliovirus; human influenza caused by new subtype; SARS.
PHEICs:
H1N1 Influenza (2019-2010)
Polio (2014-present)
Ebola
Zika Virus
Covid-19
MPox
What is a PHEIC?
Public Health Emergency of International Concern
extraordinary event which is a public health risk to other states AND potentially requires a coordinated international response
