Download Risk assessment of events involving infectious diseases

Risk assessment of events
involving infectious diseases
Preben Aavitsland
Department of Infectious Disease Epidemiology
Norwegian Institute of Public Health
at
EpiTrain V, Vilnius, October 24 2007
Contents
• Background
• Risk assessment
– what, why and when
• Risk assessment tool
– EpiRisk
• Example
What is risk assessment of events?
• Pragmatic: The determination of the
potential impact of an event by assessing
the likelihood that the event will worsen
and the impact if it does
• Risk = likelihood * impact
• Risk analysis = risk assessment + risk
management + risk communication
Why do risk assessment of events?
• Basis for risk communication
• Basis for risk management
– Appropriate use of resources
– Level of countermeasures (cost vs potential
impact averted)
• Basis for decision to notify
• Guides information gathering
When do risk assessment of events?
• Whenever there is a communicable
disease ”event” (outbreak, threat, etc)
• As early as possible
– Gather information
• Update the assessment
– Whenever new important information becomes
available
– Anyway after some time
How to do risk assessment?
• We already do it automatically and
unsystematically
• Use a systematic approach
– EpiNorth Risk Assessment of Events Tool (”EpiRisk”)
– Pilot version for testing by EpiTrain-participants
– Qualitative assessment
• Quantitative assessments usually look falsely
precise
• Document the findings
1. Event description
• Disease / syndrome
– Outbreak? Threat?
Disease?
• Agent / cause
– What is the agent or
cause?
• Time
– When did it happen?
• Place
– Where dit it happen?
• Person
– Who were involved
(gender, age,
profession, other
characteristics…)
2. Rapid disease overview
• Chain of transmission
• Time periods
– Incubation period
– Period of infectiousness
– Natural history
• Diagnosis and treatment
• General epidemiological situation
The chain of transmission
Agent
Source
Susceptible
host
Portal
of exit
Portal of
entry
Route of
transmission
Six links of the chain
Agent: virus, bacteria, fungi, protozoa, helminths, ectoparasites
Source (reservoir): Humans and aminals (symptomatic,
incubating, convalescent, asymptomatic carrier) insects,
environment (water, soil)
Portal of exit: Respiratory tract (nose, mouth), gastrointestinal
tract (anus), genitourinary tract (urethra and cervix), skin,
mucosa, placenta.
Route of transmission: Direct (contact or droplet), indirect
(vehicle, vector), airborne
Portal of entry: Respiratory tract (nose, mouth), gastrointestinal
tract (anus), genitourinary tract (urethra and cervix), skin,
mucosa.
Susceptible host: anyone who is not immune
3. Impact of event
• Assess the current and future (or as yet
undetected) impact in terms of
– Severity
– Cost
– Public interest
• Give a summary measure
Severity of event
Now
• Number of cases
(incidence rate)
• Severity of disease;
case fatality
• Age of patients
• (DALYs lost)
Future
• Assess the as yet
undetected part of the
event and the
development of the
event or the (with the
same indicators) in
the abscence of
preventive measures
 0 – 3 points
 0 – 3 points
Cost of event
Now
• Cost incurred for
treatment
• Cost incurred for sick
leave
• Cost incurred for
sequelae
 0 – 3 points
Future
• Assess the as yet
undetected part of the
event and the
development of the
event or the (with the
same indicators) in
the abscence of
preventive measures
 0 – 3 points
Public interest in event
Now
• Media interest
• Public interest,
especially parents,
children
• Politicians’ interest
• Historical context
Future
• Assess the as yet
undetected part of the
event and the
development of the
event or the (with the
same indicators) in
the abscence of
preventive measures
•  0 – 3 points
 0 – 3 points
Sum of impact
Now
Future
Severity
Cost
Interest
0 – 3 points
0 – 3 points
0 – 3 points
Severity
Cost
Interest
0 – 3 points
0 – 3 points
0 – 3 points
Sum
0 – 9 points
Sum
0 – 9 points
4. Potential for spread
• Assess the potential using
– Experience from previous events
– Expert judgement
– Analysis of the chain of transmission for this
event
– Other information
• Avoid assessing impact now
– You have already assessed impact
The chain of transmission
Agent
Source
Susceptible
host
Portal
of exit
Portal of
entry
Route of
transmission
Analyse the chain
• Every disease has its chain of
transmission
• The disease can spread only if all six
links are present
• Analyse the chain for this event (disease +
circumstances)
– Who are the sources? Infectious periods?
– How is it spread?
– Are there susceptible hosts?
• Is further spread likely?
Likelihood of spread
Conclude: What is the likelihood that the
event will spread in the abscence of
preventive measures?
•
•
•
•
Very low likelihood (It will not happen)
Low likelihood (It will probably not happen)
High likelihood (It may happen)
Very high likelihood (It will happen)
5. Preventability
• Assess using
–
–
–
–
Experience from previous events
Expert judgement
Analysis of the chain of transmission for this event
Other information
• Primary prevention
– Stop event from happening
– Reduces likelihood
• Secondary prevention
– Stop event from having consequences
– Reduces impact
The chain of transmission
Agent
Source
Susceptible
host
Portal
of exit
Portal of
entry
Route of
transmission
Possible interventions
Agent: antimicrobial treatment, disinfection
Source (reservoir): behavioural change, isolation
Portal of exit: mask, condom, bandage
Route of transmission: hand hygiene,
environmental hygiene, vector control, food and
water control, sanitation
Portal of entry: mask, gloves, gown, glasses,
condom
Susceptible host: vaccination, passive
immunisation, chemoprophylaxis, nutrition,
behavioural change
Analyse the chain
• Which link(s) can be cut to stop
transmission?
• Analyse the chain for this event (disease +
circumstances), taking each link in turn
• Conclude: Is it possible to reduce the risk?
– Primary: Reduce likelihood of spread
– Secondary: Reduce impact if it spread
6. Conclude: Current and future risk
EpiNorth Risk
Assessment of Events
Tool (EpiRisk)
Situation now
Very low
Likelihood Low
of future
spread
High
Very high
Impact
Very low
(0-2 p)
Low
(3-4 p)
High
(5-6 p)
Very high
(7-9 p)
Example
• The infectious disease doctor at the local
hospital calls you and reports that she over
the last couple of weeks have seen three
students with acute hepatitis B. They had
the same address and they seemed to
know each other. She had noted injection
scars in one of them.
1. Event description
• Event: Outbreak of hepatitis B
• Cause: Unknown, maybe shared injection
equipment or sex
• Time: November 2007
• Place: Latgale University Students’
Dormitory
• Person: Five students in the dormitory,
both genders
2. Rapid disease overview
HBV
Carriers
(asymptomatic)
Almost all (no
vaccination)
Genitourinary
tract, blood
Genitourinary
tract, through
skin
Direct contact
(sex, injection)
2. Rapid disease overview
• Time periods
– Incubation period: 45 – 180 days
– Period of communicability: Weeks before symptom
onset and for life (for carriers)
– Natural history: Mostly asymptomatic, less than 10% of
adults become carriers, then increased lifetime risk of
liver disease
• Diagnosis and treatment:
– Blood test for antigen and antibodies
• General epidemiological situation:
– Few domestic cases, many immigrant carriers
3. Impact of event
Now
Future
Severity
Cost
Interest
1 point
1 point
2 points
Severity
Cost
Interest
2 points
1 point
3 points
Sum
4 points
Sum
6 points
4. Potential for spread
High likelihood
HBV
Carriers and
newly infected
(asymptomatic)
Almost all (no
vaccination)
Genitourinary
tract, blood
Genitourinary
tract, through
skin
Direct contact
(sex, injection)
5. Preventability
Find the infected
and carriers and
stimulate to
behavioural change
Vaccinate all
students in
dormitory
HBV
Carriers
(asymptomatic)
Almost all (no
vaccination)
Genitourinary
tract, blood
Genitourinary
tract, through
skin
Direct contact
(sex, injection)
Provide condoms
and
needles/syringes
6. Conclude: Current and future risk
EpiNorth Risk
Assessment of Events
Tool (EpiRisk)
Situation now
Very low
Likelihood Low
of future
spread
High
Very high
Impact
Very low
(0-2 p)
Low
(3-4 p)
High
(5-6 p)
X
X
X
Very high
(7-9 p)
Conclusion
• Risk assessment is important in our work
• We should do it more systematically and
documented
• The EpiRisk tool has six steps and may be useful
–
–
–
–
–
–
Event description
Rapid disease overview
Impact of event
Potential for spread
Preventability
Conclusion
• Try it!
Exercise
• The groups do the story that corresponds
to their number
• Prepare a presentation in template
• If time, do the other stories also on paper
(follow the sequence 1-2-3-4-5-1-2…)
Event number 1
• The school health nurse calls you. She
has just received information that the new
cook in the school kitchen is a former
intravenous drug user with hepatitis C.
She has heard rumours that a student who
is now away from school, got hepatitis C
last month. She wants you to remove the
new cook.
Event number 2
• The local medical doctor in a small farming
community calls you. He tells you that the
local newspaper has reported rumours that
two young African asylum seekers in the
refugee’s shelter in the area are HIV
positive and have been observed dancing
in the pub with local girls. The mayor
wants the Africans removed from the
community. He fears an HIV epidemic.
Event number 3
• At the national surveillance centre you
receive reports of around 100 shigellosis
cases from several cities in one region of
the country during just one week. Usually
there are only 100 cases a year. You
believe that there may be a foodborne
outbreak related to a dairy product.
Journalists have started calling you to get
comments.
Event number 4
• Five hundred teenaged folk singers are
gathered in a village outside Vilnius for the
annual song festival. They live in tents. On
Friday evening, a young girl is admitted to
hospital with meningitis symptoms. The
next morning the hospital calls you to
inform that it is meningococcal disease,
group C. They also tells you that another,
possible case from the festival has been
admitted the same morning.
Event number 5
• The local doctor tells you that he has
detected an outbreak of measles involving
five children age 1-6 years in a group of
traveller families (Rom) that has just
arrived in their vans and settled in his city
(10 000 inhabitants). They are some 75
people. He fears further spread, and
informs you that the vaccination coverage
in the local population is around 80%.