Defining Disaster-Related Health Risk: A Primer for Prevention

Abstract

Effective disaster risk management requires not only management of the immediate problem (disaster-related injuries and disease), but also of the patient’s risk factors and of the underlying health determinants. This requires an accurate and well-validated process for assessment of the determinants of disease.
Ideally, disaster risk management is based on a prioritization process. Once hazards have been identified, they are assessed in terms of the probability and impact in terms of losses. The hazards associated with the greatest probability and impact loss are prioritized. In addition to prioritization, risk assessment also offers a process for ongoing research involving the interaction of health determinants, risk, and protective factors that may contribute to future adverse health outcomes.
Recently, assessments of health risk have become an integral part of local, state, and national emergency preparedness programs. One of the strengths of these assessments is the convening of multi-sectoral input for public health decision making and plans. However, this diversity of input also creates challenges in development of a common nomenclature for assessing and communicating the characteristics of this risk. Definitions remain ambiguous for many of the key indicators of disaster risk, especially those applied to health risk.
This report is intended as a primer for defining disaster-related health risk. This framework is discussed within a nomenclature that is consistent with international standards for risk management and public health prevention.
KeimM . Defining disaster-related health risk: a primer for prevention . Prehosp Disaster Med . 2018 ; 33 ( 3 ): 308 - 316 .

Full text

Defining Disaster-Related Health Risk: A Primer
for Prevention
Mark Keim, MD, MBA
1,2,3,4
1. Disaster Doc, LLC, Atlanta, GA USA
2. National Center for Disaster Medicine and
Public Health, Bethesda, MD USA
3. Beth Israel Deaconess Medical Center,
Disaster Medicine Fellowship, Harvard
University Medical School, Boston MA
USA
4. Rollins School of Public Health, Emory
University Atlanta, GA USA
Correspondence:
Mark Keim, MD, MBA
DisasterDoc LLC
Atlanta, Georgia USA
E-mail: mark@disasterdoc.org
Abstract
Effective disaster risk management requires not only management of the immediate
problem (disaster-related injuries and disease), but also of the patient’s risk factors and of
the underlying health determinants. This requires an accurate and well-validated process
for assessment of the determinants of disease.
Ideally, disaster risk management is based on a prioritization process. Once hazards have
been identified, they are assessed in terms of the probability and impact in terms of losses.
The hazards associated with the greatest probability and impact loss are prioritized. In
addition to prioritization, risk assessment also offers a process for ongoing research
involving the interaction of health determinants, risk, and protective factors that may
contribute to future adverse health outcomes.
Recently, assessments of health risk have become an integral part of local, state, and
national emergency preparedness programs. One of the strengths of these assessments is the
convening ofmulti-sectoral input for public health decision making and plans. However, this
diversity of input also creates challenges in development of a common nomenclature for
assessing and communicating the characteristics of this risk. Definitions remain ambiguous
for many of the key indicators of disaster risk, especially those applied to health risk.
This report is intended as a primer for defining disaster-related health risk. This frame-
work is discussed within a nomenclature that is consistent with international standards for
risk management and public health prevention.
Keim M. Defining disaster-related health risk: a primer for prevention.
Defining Risk
Risk
In simplest terms, risk is the probability that a specific outcome will occur (out of all
possible outcomes; Box 1 [available online only]). This outcome may be beneficial or
adverse. This relationship may be represented as:
priskðÞ=ZpðoutcomeÞ:
Risk represents the effect of uncertainty on outcomes.
1
Uncertainty is a state or condition
that involves a deficiency of information and leads to inadequate or incomplete knowledge or
understanding.
2
Uncertainty exists whenever the knowledge or understanding of an event,
consequence, or likelihood is inadequate or incomplete.
2
Statistical uncertainty is calculated
as the interval around the measurement in which repeated measurements will fall. Expres-
sions of risk therefore include estimations of uncertainty, as follows:
priskðÞ=ZpðoutcomeÞ±uncertainty:
Impact
In general terms, risk is conceptualized as the probability of events and the severity
of outcomes (eg, consequences) that would arise if the events take place. The severity of
consequences (usually conceptualized as losses or damage) is frequently described in terms of
impact. Correspondingly, the United Nations International Strategy for Disaster Reduction
(Geneva, Switzerland) defines impact as “the degree of severity associated with …con-
sequences….”
3
Thus, the term consequence is not synonymous with impact. Consequence is
a qualitative description of the loss, while impact is a quantitative measure of that loss.
Conflicts of interest/funding: This work was
sponsored by DisasterDoc, LLC (Atlanta,
Georgia USA), a private consulting firm
specializing in disaster research and education.
The author attests that there are no conflicts of
interest involved with the authorship and
publication of this work. The material in this
manuscript reflects solely the views of the
author. It does not necessarily reflect the
policies or recommendations of the National
Center for Disaster Medicine (Bethesda,
Maryland USA) or the Department of Defense
(Washington, DC USA).
Keywords: disaster; health risk; prevention; risk;
risk assessment
Received: April 8, 2017
Revised: August 29, 2017
Accepted: September 24, 2017
doi:10.1017/S1049023X18000390
SPECIAL REPORT
Prehospital and Disaster Medicine

Risk Assessment
Risk assessment is the process of estimating the probability of an
outcome. Risk is assessed as a function of the probability that an
adverse event (referred to as a hazard) and its resultant impact will
occur during a given timeframe. This relationship is described as
follows in what is commonly referred to as the “risk equation:”
4
pRðÞ=ZpH´IðÞ±uncertainty
where, R =risk; H =hazard incidence; and I =degree of impact.
Hazards are defined as “an agent or a situation…with the
inherent capability to have an adverse effect.”
5
Examples of health
hazards include: viruses, chemicals, tobacco, and even direct
sunlight. Risk is the joint probability that (in the future): (1) one of
these hazards will occur; and (2) that there will be a resultant
impact.
Risk Management
According to ISO 31000 (International Organization for
Standardization; Geneva, Switzerland), a set of international
standards relating to risk management, risk management is the
activity directed toward assessing, communicating, and treating
risks.
1
It is the systematic approach and practice of managing
uncertainty to minimize potential harm and loss. This involves
a process of evaluating alternative actions, selecting options, and
implementation guided by risk assessment. The decision making
will incorporate scientific information, but also requires value
judgements (eg, on the tolerability and reasonableness of costs;
Figure 1).
Risk Assessment
Risk assessment is the process of the probability an outcome,
under a specific set of conditions, and for a certain timeframe.
Thus, risk assessments are intended to express risk in terms of
forecasting the statistical probability for a specific, measurable, and
time-based outcome.
Risk Communication
Risk communication is an interactive process involving the
exchange among individuals, groups, and institutions of infor-
mation and expert opinion about the nature, severity, and
acceptability of risks and the decisions taken to combat them.
6
Risk Treatment
Risk treatment measures are put in place to control risk, whenever
possible. These, in turn, include:
6
∙Risk Avoidance - avoiding the risk altogether;
∙Risk Reduction - reducing the negative effect of the risk;
∙Risk Transfer - transferring the risk to another party; and
∙Risk Acceptance - accepting some or all of the consequences
of a risk.
Defining Health Risk
Health, Disease, and Illness
According to the World Health Organization (Geneva,
Switzerland), “Health is a state of complete physical, mental, and
social well-being and not merely the absence of disease or infir-
mity.”
7
Disease is defined as “a deviation from normal health that
derives from an identifiable pathological process and which the
patient experiences as an illness.”
5
In comparison, illness is the
“subjective sense of feeling unwell that often motivates a patient to
consult a physician.”
5
Casual Factors for Disease
Disease does not occur randomly. It is caused when vulnerable
hosts are exposed to an environment containing agents that are
hazardous to health. It is therefore possible to study the causal
pathways involving the agent, host, and environment, including
both risk and protective factors. Causal factors are any behavior,
omission, or deficiency that if corrected, eliminated, or avoided
probably would have prevented the disease. Figure 2 illustrates
how disease is caused by a complex interaction between the
person (host), the disease agent (hazard), and the environment
(exposure).
8
Health Hazards
Health hazards are defined as an agent or a situation that, when
exposed to a human, has the inherent capability to cause an adverse
health outcome (disease), resulting in morbidity (illness and/or
injury) and mortality (death).
Biological hazards which transfer infection are those micro-
biological organisms (bacteria, viruses, parasites, or fungi) that
cause infectious disease.
9
Hazards which transfer energy (mechanical, chemical, thermal,
or radiological) are usually associated with injury.
9
In some cases, environmental hazards cause injuries such as
dehydration, malnutrition, drowning, and hypothermia (through
the absence of essential requirements for life such as water, food,
oxygen, or heat, respectively).
9
Categories of Disease
Three major categories of disease include: communicable disease,
non-communicable disease, and injury.
Communicable disease is an infectious disease that can be
passed (transmitted) from person to person. Infectious disease is
“caused by pathogenic microorganisms, such as bacteria, viruses,
parasites, or fungi; the diseases can be spread, directly or indirectly,
from one person to another.”
10
Non-communicable diseases, also known as chronic diseases,
are not passed from person to person. They are commonly
associated with exposures related to lifestyle (eg, diet, exercise,
smoking, or a workplace) and are typically of long duration and
generally slow progression. Four main types of non-communicable
diseases include cardiovascular diseases (like heart attacks and
stroke), cancers, chronic respiratory diseases (such as chronic
obstructive pulmonary disease and asthma), and diabetes.
Exacerbations of endemic, non-communicable diseases are com-
mon among all disasters.
Injury is a category of disease “caused by acute exposure to
physical agents such as mechanical energy, heat, electricity,
chemicals, and ionizing radiation interacting with the body in
amounts or at rates that exceed the threshold of human
tolerance.”
11,12
Keim © 2018 Prehospital and Disaster Medicine
Figure 1. Components of Risk Management.
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2 Defining Disaster-Related Health Risk

Some experts consider that the interval between exposure
and the appearance of injury can be relatively long, such as in
poisoning from carbon monoxide, alcohol abuse, or heavy
metals. Acuteness is certainly a factor: the shorter the time from
exposure to a hazard to its physical effects, the more likely
the resulting condition will be called “injury”rather than
“disease.”This distinction is somewhat arbitrary, but it is
conceptually useful for classification, research, and policy, as well
as this discussion.
Natural History of Disease
The fundamental principle upon which disease management is
based is a recognition of distinct stages in the development of
disaster-related disease. If left untreated, a disease will evolve
through a series of stages that characterize its natural history. But
if an intervention is applied, the natural history is modified,
producing a typical clinical course for the condition.
Figure 3 represents the “natural history of disease,”the concept
of disease as a process that unfolds over time in a series of steps.
5
Effective disease management requires not only management of
the immediate problem, but also management of the patient’s risk
factors, and finally of the underlying determinants.
Figure 3 depicts the relationship between health determinants,
risk factors, and disease. After exposure to a hazard (noted by the
dark arrow), there is a theoretical point at which the disease
process may begin. Symptoms may appear after a delay that can
vary from seconds (as with injury) to days (as with infections) to
years (as with cancer). The patient may interpret their symptoms
as indicating an illness and may seek professional care. Shortly
after a medical diagnosis, therapy is normally begun and
short- and longer-term outcomes can be recorded.
Risk Factors for Disease
The definition of a risk factor is “any attribute, characteristic, or
exposure of an individual that increases the likelihood of an out-
come, in this case developing a disease.”
13
Risk factors associated
with vulnerability are those characteristics inherent to the person
that increase the statistical probability that a person will develop
disease. The term risk factor is also used to describe an exposure
variable such as the amount of a factor to which a group or indi-
vidual was exposed; in contrast to the dosage, the amount that
enters or interacts with the organism.
Some health-related risk factors have a direct and probabilistic
effect on the likelihood of an adverse outcome. Others form part of
Keim © 2018 Prehospital and Disaster Medicine
Figure 2. Causal Factors for Disease.
8,17
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Keim 3

a complex causal pattern, as with the effect of age, in which health
status, disability, and education interact with numerous other
factors. But, these risk factors themselves also have causes, called
health determinants.
Health Determinants
Health determinants refer to underlying characteristics of society
that ultimately shape the health of individuals and communities.
These can be thought of as the “causes of the causes”of disease,
or as the origin of the causal chain. But the term should not be
misconstrued to imply inevitability. Determinants include non-
specific factors (eg, poverty or lack of educational opportunities)
and policies aimed at improving health, in general, rather than
particular diseases.
Health Risk (R
H
)
The epidemiological definition of health risk is “the probability
that an adverse health event (disease) will occur”(eg, that an
individual will become ill or die within a stated period of time or
age). It is formally defined as the proportion of initially disease-
free individuals who develop disease over a defined period of
observation. This risk is described in terms of disease incidence
rate (eg, the measure of the number of new cases per unit of time):
thus;RH=ZpDðÞ
where, R
H
=health risk, and D =disease incidence (cases
over time).
When applied to public health, health risk is the probability
that, in a certain timeframe, an adverse outcome will occur among
a population that is exposed to a hazardous agent. Placed in terms
of health risk, disease is caused by the complex interaction of risk
and protective factors associated with:
∙Agent (hazards);
∙Host (vulnerabilities); and
∙Environment (exposure).
Health Impact
The impacts of health hazards are customarily assessed
according to factors associated with the interaction between
the environment and the host population (respectively) as
follows:
8,14
∙Exposure dose:
○magnitude of the hazard itself (eg toxicity, virulence,
or potential energy); and
○amount of hazard contacted over time (dose rate).
∙Vulnerability of the host population to that specific hazard:
○susceptibility to disease onset; and
○severity of disease after onset.
Impact is a measure of disaster outcome.
3
The incidence of
disease is one example of a measure of health outcome and thus
a measure of impact. Health impact (I
H
) is expressed as a rate and
measured in terms of disease incidence p(D) resulting from
exposure and vulnerability to a particular hazard:
thus;pðIHÞ=ZpE´VðÞ
where, p(I
H
)=health impact; E =exposure dose; and
V=vulnerability of population.
Assessing Health Risk
Risk assessment is the process of estimating the probability an
outcome (in this case, impact of a chemical, physical, micro-
biological, or psychosocial hazard on a specified human popu-
lation) under a specific set of conditions and for a certain
timeframe. Thus, health risk assessments are expected to express risk
in terms of the probability of a specific health outcome (bad or good).
However, it is important to recognize that health risk is not
synonymous with disaster risk.
Defining Disaster Risk
Disasters
A disaster is “a serious disruption of the functioning of a
community or a society causing widespread human, material,
economic, or environmental losses that exceed the ability
(or capacity) of the affected community or society to cope using its
own resources.”
3
These losses result in human needs. Thus, per
this model, disasters are a mismatch of needs and resources.
Keim © 2018 Prehospital and Disaster Medicine
Figure 3. Natural History of Disease.
5
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4 Defining Disaster-Related Health Risk

Disasters are defined as a fundamental mismatch of needs
and resources resulting in losses. Disaster risk is defined as the
probability of this mismatch of needs and resources. Disasters
are considered as part of a continuum of societal effects that
result from this mismatch.
Disaster risk is a measure of not only the probability of disaster
impact, but also includes the capacity of the population to avoid
a mismatch of needs (caused by losses) and resources (capacity
for resilience).
Emergencies, Disasters, and Catastrophes
Emergencies are defined as a mismatch of societal needs and resources
that may be effectively resolved using its own resources. Along that
same continuum, disasters are described as a mismatch of needs and
resources that may be effectively resolved, only with external assistance
to the affected population. Accordingly, catastrophes have been
further described as a mismatch of needs and resources that are not
effectively resolved, even with external assistance to the affected
population.
15
The goal of reducing disaster risk is to lessen the
likelihood of occurrence for this entire continuum of events.
Categories of Disasters
The Sendai Framework recognizes two groups of disasters: natural
and human-induced. There are five sub-types of disasters: three
induced by natural hazards (biological, hydro-meteorological, and
geological) and two induced by human activity (technological
and societal).
16
Disaster Risk
Disaster risk is widely assessed by national emergency manage-
ment agencies and expressed in terms of societal outcomes that
relate to social, health, economic, political, and national security
concerns. Disaster risk is based upon the general risk equation:
4
RD
ðÞ=ZpHðÞ´pIðÞ
where, R
D
=risk of disaster; H =hazard; and I =impact of that
hazard.
However, per the definition of disaster, risk is based upon the
probability of a mismatch between needs (caused by impact), as
compared to resources (eg, capacity) available to meet those needs
(without additional losses). To summarize:
∙Hazards create losses:
○The severity of losses is expressed in terms of impact;
∙Impacts create needs:
○Abilities required to meet the needs are expressed in
terms of capabilities; and
∙Capabilities meet needs:
○The measure of a capability that is available over time is
expressed in terms of capacity.
Disaster risk (R
D
) is therefore expressed as:
RD=pDisaster hazardðÞ´pDisaster impactðÞ;or
RD
ðÞ=ZpHðÞ´pIðÞ:
Disaster losses create needs. Capacity is used to meet these
needs. Disaster risk is defined as the probability that a hazard will
occur resulting in needs that will exceed resources. Thus, disaster
impact is the net risk that results when needs exceed resources.
In other words;pðDisaster impactÞ
=ZpðDisaster needs -Disaster resourcesÞ;
thus;RD=Zp½ðDisaster hazardÞ
´pðDisaster needs -Disaster resources
Effective disaster risk management requires not only manage-
ment of the immediate problem (disaster-related injuries and dis-
ease), but also of the patient’s risk factors and of the underlying
health determinants. This requires an accurate and well-validated
process for assessment of the determinants of disease. Disaster risk
management is the systematic process of using capacities in order to
lessen the adverse impacts of hazards and the possibility of disaster.
Table 1,
17-19
depicts the functional relationship between the
various components of disaster risk.
Hazards (H)
Disaster hazards are defined as “a dangerous phenomenon,
substance, human activity, or condition that may cause loss of life,
injury, or other negative health impacts; property damage; loss of
livelihoods and services; social and economic disruption; and/or
environmental damage.”
3
The Sendai Framework recognizes two groups of hazards:
natural and human-induced. There are five sub-types of hazards:
three induced by natural hazards (biological, hydro-meteor-
ological, and geological) and two induced by human activity
(technological and societal).
16
A disaster might involve a
IMPACT
Needs Resources
Exposure Vulnerability Capacity (for resilience)
HAZARD Concentration
or Magnitude
Time Susceptibility Severity Avoidance Reduction Transfer Retention
Absorption Adaptation Transformation
Dose Response Treatment
Increases
Risk
Increases risk Increases risk Decreases risk
Keim © 2018 Prehospital and Disaster Medicine
Table 1. Relationship between the Components of Disaster Risk
17-19
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Keim 5

combination of these hazards. For example, earthquake-related
damages to natural gas infrastructure often result in an increased
human exposure to fire hazards.
Impact (I)
United Nations International Strategy for Disaster Reduction also
defines disaster impact as “the degree of severity associated with
disaster consequences, often measured in terms of number of fatalities
and injuries; functionality of critical facilities and community lifelines;
property and environmental damage; economic, social, and political
disruptions; and size of the area or number of people affected.”
3
Thus, disaster impact is a measure of the resultant net balance
of outcomes resulting from human needs (caused by exposure and
vulnerability) and human resources (capacity) that are available to
meet those needs.
Exposure (E)
Exposure is defined as “proximity or contact with a source of
a disease agent in such a manner that effective transmission of the
agent or harmful effects of the agent may occur.”
20
Exposure is a
function of the dose rate (magnitude/volume/time) of the hazard
and the duration of exposure over time.
13
For health, exposure is
calculated as a function of hazard dose.
Exposure assessment is the qualitative and/or quantitative
evaluation of the likely contact with biological, chemical, and
physical agents (hazards). This assessment involves identification
and evaluation of the human population exposed to a hazardous
agent, describing its composition and size, as well as the type,
magnitude, frequency, route, and duration of exposure.
21
Exposure science (eg, exposure and dose reconstruction) is a
well-developed field of empirical investigation in public health and
medicine. There are three commonly accepted routes of human
exposure: inhalation, ingestion, and direct contact to the body.
Dose
Dose is the amount of a substance available for interactions with
metabolic processes or biologically significant receptors after
crossing the outer boundary of an organism.
21
Hazard dose asso-
ciated with physical agents (involving a transfer of energy to the
body; ie, kinetic, nuclear, electromagnetic, chemical, and thermal
energy) is calculated as a function of the hazard magnitude and the
contact rate. Contact rates vary according to the route of exposure
(eg, respiratory rate, ingestion, or absorption.)
For example, chemical dose is calculated according to the
concentration (mass/volume) and contact rate (mass/volume/
time) multiplied by the duration of exposure (time):
thus;pEðÞ=ZpdoseðÞ

pEðÞ=pdoseðÞ=Zpdose=timeðÞ´pduration of exposureðÞ

:
In comparison, dose of microbiological hazards (pathogenic
bacteria and viruses) is expressed as an “infectious dose,”the
amount of pathogen (measured in number of micro-organisms)
required to cause an infection in the host.
14
Populations may also be exposed to a hazard, without any
adverse effect. Thus, the term “exposure”is not synonymous with
the term “affected”(as per criteria used by the Center for Research
on the Epidemiology of Disasters [Brussels, Belgium] EM-DAT
database).
22
Vulnerability (V)
Vulnerability is defined as “the characteristics and circumstances
that make a community or individual, or a system or asset,
susceptible to the damaging effects of a hazard.”
3
Given the exact
same exposure, some assets or individuals belonging to the
population are more likely than others to suffer loss (risk) than
others. This variability of risk is a function of the vulnerability
of the population.
Vulnerability is considered to be that set of risk and protective
factors inherent to the individual. It should not be confused with
capacity which represents external resources. Unlike exposure, the
vulnerability of the individual does not change according to geo-
graphical location (environment). It’s also important to recognize that
some factors recognized as vulnerability (eg, age, health status, or dis-
ability) may actually represent a collinearity for higher risk of exposure.
Vulnerability has been categorized according to four sets of
attributes:
17
∙Demographics (eg, age, gender, and family position);
∙Education and personal experience (eg, educational level and
disaster training);
∙Race, language, and ethnicity (eg, minority status in the
affected population and language barriers); and
∙Health status (eg, chronic illness, physical disability,
malnutrition, mental illness, and dependence upon life-
sustaining treatment).
Vulnerability to health hazards has been described as either
intrinsic or acquired.
23
Examples of intrinsic factors that influence
human vulnerability (V
i
) include: age, gender, genetics, and
ethnicity. Examples of acquired factors that influence human
vulnerability (V
a
) include: health status, education, disability, and
immunization status:
thus;pVðÞ=ZpXVi¼+XVa¼

:
Vulnerability to adverse health effects is known to vary among
individuals according to two key factors: susceptibility and sever-
ity.
14
Given the same exposure, some individuals are more
susceptible to the onset of disease than others. And then subse-
quently, given the same disease onset, some individuals
(eg, immunocompromised, extremes of age, or co-morbidity) tend
to suffer a more severe course of illness than others, resulting in
prolonged impairment, permanent disability, or death.
Capacity (C)
Capacity is defined as “the combination of all the strengths,
attributes, and resources available in a community, society, or
organization that can be used to minimize (adverse outcomes)
following exposure to a hazard.”
3
Although this definition is here
narrowed to risk acceptance, capacity may also be used to treat risk
in other ways. In other words, capacity represents resources that
are used for risk treatment. Capacity is therefore considered as an
input to the system that influences disaster outcome.
Capacity has been described to exist at the following hier-
archical organizational levels: individual, household, community,
and society.
18
Capacity has also been described to include four major cate-
gories of resources:
18
∙Economic (eg, occupation, income, savings, and health
insurance);
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6 Defining Disaster-Related Health Risk

∙Material (eg, durable goods, equipment and supplies,
utilities, shelter, and transportation);
∙Behavioral (eg, psychological, emotional, cognitive, and
developmental); and
∙Sociopolitical (eg, social capital, status, political influence,
and ethnicity).
Populations apply individual, household, community, and
societal capacity to reduce risk at every of possible stage of inter-
vention (eg, avoidance, reduction, transfer, and acceptance).
18
This capacity includes economic, material, behavioral, and socio-
political resources for reducing disaster risk at each stage. Contrary
to misconception, capacity is applied not only during residual risk
during response and recovery, but also throughout other phases of
emergency management, including: prevention, preparedness,
mitigation, response, and recovery.
Capacity is most commonly represented as an asset inventory
(ie, number of meals, amount of water, or number of tents).
However, this application recognizes only resources. It does not
take into consideration the efficiency of operations that implement
capacity and effectively increase certainty of outcome. In other
words, mere existence of a capacity does not ensure its maximum
utilization. On the contrary, the efficient utilization of capacity is
notoriously challenging during emergency response operations.
Capacity is measured as a performance rate over time (ie,
number of meals delivered per day; liters of water delivered per
person - per day; or number of tents erected per day). Thus, the
maximum capacity (not the resources) of the population represents
a rate limiting step for reducing disaster impact.
18
Differentiating Capacity from Capability
An objective is defined as, “A purpose to be achieved, or a result to
be obtained.”
24
A capability is, “the ability to achieve a desired
operational effect”(purpose or result) “under specified standards
and conditions through combinations of means and ways to per-
form a set of tasks.”
24
Capability is considered as an output of the
system created by inputs of resources into an organizational
process.
Capability should not be confused with capacity. Objectives are
outcomes to be achieved.
Capability is the ability to accomplish an objective. Capacity is
the rate at which resources become available to accomplish
an objective. Consider this contrast of capacity and capability.
Imagine that there are two resources of water (one is a 15-liter
barrel and one is a 300 ml glass) that one may refill only once daily.
One’s objective is to stay alive. The capability of the water is to
hydrate the human body. Thus, both resources have that exact
same capability of hydration. However, in terms of volume, the
barrel is 50 times greater than that of the glass. And, in terms of its
effect as a rate limiting factor for accomplishing the objective
(ie, survival), the capacity of the barrel is 15 liters/person/day
(adequate according to international standards) as compared to
only 300ml/person/day from the glass, which cannot sustain life.
The objective was limited by the capacity of the resources, and not
necessarily its capability.
Consider a final example contrasting capacity and capability, in
which there has been a mass-casualty incident at a school resulting
in many seriously injured pediatric patients. The objective is to
provide adequate hospital care for all patients. While some area
hospitals may be able to offer care, they do not have the capability
to treat pediatric patients. In comparison, the one small pediatric
hospital in the city has the capability to treat pediatric trauma, but
does not have enough capacity (eg, care givers, equipment, and
supplies) to adequately treat all of the patients at once. Thus,
excess mortality may occur as a result of this mismatch in capability
(to accomplish the goal) and the capacity (to do so efficiently).
This also implies that “capacities as an output do not tell us any-
thing about the extent to which these capacities are actually used in
case of a disaster (or a simulation), and –even more importantly –
if they are effective.”
18
Resilience
There is currently a myriad of definitions and interpretations for
the term resilience.
18
Despite its current influence, no agreement
exists over the exact meaning of the concept. The United Nations
International Strategy for Disaster Reduction defines resilience as
the ability of a system, community, or society exposed to hazards to
resist, absorb, accommodate to, and recover from the effects
of a hazard in a timely and efficient manner, including through
the preservation and restoration of its essential basic structures
and functions.
3
A resilient control system is one that maintains: (1) state
awareness, and (2) an accepted level of operational normalcy in
response to disturbances, including threats of an unexpected
nature. This ability to recover is the one fundamental concept
shared among these various definitions of resilience. However,
characterization of this recovery varies widely among the various
sectors. Thus, resilience may reasonably be defined as recovery
of an individual, household, community, or society to a state
of accepted level of normalcy. Thus, disaster capacity may
be expectedly referenced as “capacity for resilience,”or resilience
capacity.
18
Capacity for Resilience
Resilience is the ability of a system, community, or society exposed
to hazards to resist, absorb, accommodate to, and recover from the
effects of a hazard in a timely and efficient manner, including
through the preservation and restoration of its essential basic
structures and functions.
3
Populations apply capacity to reduce
risk and improve resilience before and after the disaster event itself.
Capacity is applied not only during the post-event setting for
response and recovery, but it is also used throughout pre-event
phases of emergency management, including: prevention, pre-
paredness, and mitigation. Resilience capacity is used to minimize
losses by avoiding hazards, reducing exposures, transferring risk,
and finally accepting risk (eg, response and recovery; Table 1).
Components of “resilience capacity”applied to risk acceptance/
retention include: absorptive, adaptive, and transformative capa-
cities.
18
These three elements commonly vary along a continuum
related to the intensity of the change necessary for recovery, as well
as the transactional cost that may be associated with doing so.
On one end of the spectrum is absorptive capacity, the measure
of an ability to absorb and assimilate the effects of the hazard.
Absorptive capacity is based upon the stability of the system and its
function to buffer impact without significant change in the process
itself. Adaptive capacity requires less stability and more flexibility
as required in order to make incremental adjustments in the
process so that outcomes will improve. And finally, transformative
capacity is a measure of the ability to transform or change processes
entirely to optimize outcome. Transformative capacity requires the
highest degree of system flexibility and comes at the highest
transactional cost.
18
Prehospital and Disaster Medicine
Keim 7

Individuals, households, communities, and societies each tend
to apply these three elements of capacity in a nearly sequential
order. Initially, those systems affected respond by rapidly absorb-
ing inputs (ie, patients or displaced people) to a given threshold
(also known as “surge capacity”); then, adapting to accommodate a
larger, more efficient or more effective version of the same process
(eg, coordination with local emergency response); and then finally,
transformation of the entire process into one that is more
suitable for the expected outcome (ie, multi-national humanitarian
assistance).
Differentiating between the Risk of Hazards, Health Effects, and
Disasters
Ambiguity regarding the context of risk is a common challenge for
risk assessment. Some assessments may incorrectly equate the
incidence of the hazard with the risk of disaster. This approach
tends to neglect the role of other factors that contribute to the
hazard’s impact (eg, exposure, vulnerability, or capacity). Other
risk assessments inaccurately equate the risk of adverse health
outcome with the risk of disaster (or vice versa). It’s therefore
important to differentiate between the risks of hazards, health
effects, and disasters so that the context for the risk assessment
may be accurately established as the foundation for reproducibility
in subsequent investigations and interventions. Table 2 offers
a comparison of the descriptions for risk as applied to hazards,
health, and disasters.
Differentiating Health Risk from Disaster Risk
Disasters are defined by a characteristic mismatch of needs and
resources. Table 2 compares health risk and disaster risk as applied
to capacity. Health risk differs from disaster risk in that (by
definition) disaster risk is a measure of not only the probability of
adverse health outcomes (eg, health risk), but also the ability
of the target population to avoid a mismatch of health needs
(caused by losses) and health resources (eg, the capacity needed to
avoid disease).
Differentiating Disaster Hazards from Health Hazards
Besides health risk, it is also important to differentiate disaster
hazards from health hazards. Disaster hazards represent the dan-
gerous phenomenon (eg, wildfire, flood, pandemic, and terrorism)
responsible for causing the disaster event (ie, a mismatch of needs
and resources). In comparison, health hazards (ie, heat, water,
viruses, mechanical force, chemicals, and radiation) are created by
disaster hazards. Health hazards are then responsible for causing
disease (including injury) through a specific route of exposure and
pathological mechanism.
Health hazards are defined as “an agent or a situation…with
the inherent capability to have an adverse effect.”
5
Hazard risk,
p(H), is calculated from the annual hazard incidence and is
described in terms of number of hazard occurrences per year. In
comparison, the epidemiological definition of health risk is “the
probability that an adverse health event (disease) will occur”within
a stated period of time or age.
5
This differentiation is important during the assessment process
as the specific mechanism of injury is considered for attribution of
disaster-related morbidity and mortality and development of
effective countermeasures that specifically address disaster-related
health risk.
Differentiating Health Risk (R
H
) from Disaster-Related Health
Risk (D
H
)
Health risk is customarily reported as the proportion of initially
disease-free individuals who develop disease over a defined period
of observation. Health risk is calculated as the annual case inci-
dence rate (eg, mortality rate or morbidity rate) and described as
the proportion of individuals within a given population who
develop disease over a defined time. In other words, health risk is
equal to the likelihood of disease during a given timeframe:
thus;pRH
ðÞ=pDðÞ
where;pRH
ðÞ=health risk;pDðÞ=disease incidence:
Note that the disaster risk equation differs from the general risk
equation in that disaster risk also includes the effect of capacity in
its determination of impact, whereas the general risk equation
(and health risk assessments, in general) deal only with pre-event
probability. These calculations therefore do not take into
consideration various elements of risk treatment that may be
applied (eg, risk avoidance, reduction, transfer, and acceptance).
It is therefore important to recognize that health risk is not
synonymous with disaster-related health risk. While both
represent health-related outcomes, the outcome predicted by
disaster-related health risk is the post-event probability of disease
given a mismatch in terms of collective or societal needs and
Risk of Hazard Occurrence,
H, as an Outcome Health Risk, R
H
Disaster Risk, R
D
, Risk of Needs/
Resource Mismatch
Disaster-Related Health
Risk, D
H
Hazard Incidence
p(H)
Disease incidence,
R
H
=p(D)
Disaster incidence,
p(R
D
)
Disease incidence, p(D),
given R
D
has occurred
p(Hazard) R
H
=p(Hazard) × (Impact)
where, p(Impact) =
p(Exposure) × p(Vulnerability)
R
D
=p(Hazard) × p(Impact)
where, p(Impact) =p(Needs -
Resources)
D
H
=p(Hazard) × p(Impact)
where, p(Impact) =p(Needs -
Resources)
p(H) R
H
=p(H) × p(I
H
)
where, p(I
H
)=p(E × V)
thus, R
H
=p(H) × p(ExV)
R
D
=p(H) × p(I)
where, p(I) =p(E × V) - p(C)
thus, R
D
=p(H) × p[(E × V)-C]
D
H
=p(H) × p(I
H
)
where, p(I
H
)=p[(E × V) - C]
thus, D
H
=p(R
H)
-p(C)
Keim © 2018 Prehospital and Disaster Medicine
Table 2. A Comparison of Hazard Risk, Health Risk, and Disaster Risk
Prehospital and Disaster Medicine
8 Defining Disaster-Related Health Risk

resources. On the contrary, in this instance, health risk is con-
sidered as the pre-event probability of disease, in absence of any
attempts at reducing or treating the risk.
Thus, per this relationship, health risk represents the prob-
ability of health needs, but it does not represent the disaster
resources (capacity) available to address those needs (treat the risk).
Disaster-related health risk is represented as the health risk
minus the risk that can be ameliorated by capacity. In other words:
DH=pRH
ðÞ-pCH
ðÞðTable 2Þ:
Accordingly, disaster-related health impact (I
D
) is a function of
exposure, vulnerability, and capacity of the population at risk:
pID
ðÞ=ZpEðÞ´pVðÞ

-pCð Þ:
This equation represents the risk of adverse outcome faced by a
vulnerable population (P) when disaster-induced needs (caused by
hazard exposure) exceed the resources (capacity) of the population.
As indicated in Table 2, health risk is dependent upon the
probability of the hazard and the resultant health impact. In
comparison, disaster-related health risk includes both the like-
lihood of a mismatch between health impact and the capacity
necessary to avoid disease. In effect, disaster-related health risk is
measured as the net health risk present when health impact
exceeds capacity. Thus, for disasters, the disaster-related health
impact must include: not only health impacts expected to occur
from being vulnerable to a hazard exposure, but also the supple-
mental risk that accrues due to a mismatch in acute health needs
and the capacity to avoid disease.
Conclusion
Assessments of health risk have become an integral part of local,
state, and national emergency preparedness programs. One of the
strengths of these assessments lies in that they typically bring
together multi-sectoral input for public health decision making
and plans. However, this diversity of input also creates challenges
in development of a common nomenclature for assessing and
communicating the characteristics of this risk.
A standard nomenclature is needed for communicating
disaster-related health risk that is consistent with international
standards for risk management and the advancement of public
health science. This report is intended as a primer for defining
disaster-related health risk. This framework is discussed within a
nomenclature that is consistent with international standards for
risk management and public health prevention.
Supplementary material
To view supplementary material for this article, please visit https://
doi.org/10.1017/S1049023X18000390
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