Concepts of Field Epidemiology in Preparation for Response to Infectious Disease Outbreak in Rural Rajasthan, India
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International Journal of Science and Healthcare Research
Vol.5; Issue: 2; April-June 2020
Website: ijshr.com
Review Article ISSN: 2455-7587
Concepts of Field Epidemiology in Preparation for
Response to Infectious Disease Outbreak in Rural
Rajasthan, India
GV Fant
Visiting Professor, Public Health (Epidemiology & Biostatistics), Jodhpur School of Public Health (JSPH);
Executive Director, Society for Epidemiology at JSPH;
Practicing Public Health Epidemiologist in Northern Virginia, USA
ABSTRACT Family Welfare (MoHFW) continues to
work with the WHO Country Office-India
Recent World Health Organization (WHO)- “on preparedness and response measures for
India COVID-19 Situation Update Reports have COVID-19, including surveillance and
documented the status of the epidemic. COVID- contact tracing, laboratory diagnosis, risk
19 is an infectious disease outbreak of
communications and community
significant impact throughout India. There are
other infectious diseases, also circulating in engagement, hospital preparedness,
nature that may or may not become a disease infection prevention and control (IPC) and
cluster that leads to an outbreak. Given the implementation of containment strategies”.
[2]
current situation, this is an appropriate time to
review the concepts of field epidemiology to The high categorization of COVID-
assist in epidemiologic efforts in response to 19 cases and deaths in Rajasthan [1] is a
infectious disease outbreaks. The main purpose concern. Part of the response effort is likely
of this review is to succinctly describe some to include field epidemiological services.
main concepts of field epidemiology to assist COVID-19 is an infectious disease outbreak
public health professionals preparing to
of significant impact throughout India.
investigate infectious disease outbreaks in rural
Circulating in nature, there are other
Rajasthan or similar regions in India.
infectious diseases that may or may not
Key Words: Field Epidemiology, Outbreak, become a disease cluster that leads to an
Epidemic Curve, Epidemiologic Disease outbreak among humans. Given the current
Control Methods, Team-work situation, this is an appropriate time to
review the concepts of field epidemiology to
INTRODUCTION assist in epidemiologic efforts in response to
Recent World Health Organization infectious disease outbreaks. In the past five
(WHO)-India COVID-19 Situation Update years, a search of Google Scholar did not
Reports have documented the status of the reveal any prior efforts to describe the
epidemic. [1,2] In the report from April 5, concepts of field epidemiology for use in
2020, 3,577 COVID-19 cases (including Rajasthan, India.
some cases from outside of India) had been The purpose of this review is to
reported in 29 states/union territories, and succinctly describe the main concepts of
there were 83 reported deaths from the field epidemiology for public health
disease. The next report, dated April 12, emergency professionals and community
2020, showed some differences: 8,447 leaders responding to any infectious disease
confirmed COVID-19 cases in 31 outbreak in rural Rajasthan. This paper is
states/union territories and 273 reported organized using four sections: Field
deaths. The Indian Ministry of Health and Epidemiology and related concepts;
International Journal of Science and Healthcare Research (www.ijshr.com) 47
Vol.5; Issue: 2; April-June 2020
GV Fant. Concepts of field epidemiology in preparation for response to infectious disease outbreak in rural
Rajasthan, India
Outbreak Investigation, the Chain of complete a clinical picture of disease, and
Infection and the Epidemic Curve; use epidemiologic methods to search for
Overview of Epidemiologic Disease Control causes of disease.
Methods; and Team Approach to Outbreak Functionally, field epidemiology is
Investigation and Emergency Response. used in situations where a cluster of
communicable or infectious disease cases
Section 1: Field Epidemiology and have been found in a population that was
Related Concepts previously not impacted by the disease. [10]
Epidemiology is considered the Epidemiologists travel to the location of the
fundamental science of public health disease cluster, along with other public
practice and population health. [3,4] Let us health professionals and medical
define what we mean by the term: professionals, to help characterize the
Epidemiology is the study of the distribution disease, control the disease, and institute
and determinants of health-related states or public health control measures in the
events in a specified population, and the community. The medical treatment of those
application of this study to the control of the community members in need may, also, be
health problem in the population. [5] This provided by medical professionals.
highly quantitative science is known for its There are many terms used by field
methods of action-orientation epidemiologists in the course of
epidemiological intelligence and has a investigating communicable disease in a
history of significant events such as: [6-8] community. These terms are defined as
such: [11,12]
Acknowledgement of the environment
in disease (460-370 BCE) Mortality: death
Compilation of mortality statistics
(1662) Morbidity: any departure, subjective or
Publication of “Diseases of Workers” objective, for a state of physiological or
(1700) psychological well-being; in this sense,
Containment of cholera at the water- sickness and illness may be used as
pump handle at Broad Street (ca. 1850) synonyms.
Characterization of the influenza
pandemic (1918) Prevalence: the number or proportion of
Elimination of smallpox (1977) cases or events or attributes among a given
population; describes the number of existing
Recognition of “Ebola Fighters” as the
cases in population at a given time-period;
“Persons of the Year” by Time
prevalence rate.
Magazine (2014)
Incidence: measure of the frequency with
The scientific, action-oriented focus
which new cases of illness, injury, or other
of epidemiology has been recognized to
health condition occurs among a population
have seven uses in the broad public health
during a specific time period; describes the
field. [6,9] To understand the health status of
number of new cases in a population at a
a population and its utilization of health
given time-period; incidence rate.
services, epidemiology is used to study the
history of health in a population, diagnose
Attack Rate: form of incidence that
the health of a community, and examine the
measures the proportion of persons in a
workings of health services by the
population who experience an acute health
population. To understand the causes of
event during a limited period.
disease, epidemiology is used to estimate
disease risk in the population, identify
syndromes, provide scientific evidence to
International Journal of Science and Healthcare Research (www.ijshr.com) 48
Vol.5; Issue: 2; April-June 2020GV Fant. Concepts of field epidemiology in preparation for response to infectious disease outbreak in rural
Rajasthan, India
Virulence: the ability of an infectious agent categorical, discrete, or continuous, and it is
to cause severe disease, measured as the from these public health variables that
proportion of persons with the disease who calculations are performed.
become severely ill or die.
Section 2: Outbreak Investigation, the
Infectivity: the ability of an infectious agent Chain of Infection, and the Epidemic
to cause infection, measured as the Curve
proportion of persons exposed to an During an outbreak investigation,
infectious agent who become infected. the central aims of epidemiologic activities
are to find the cause of the disease outbreak
Herd Immunity: the resistance to an and to stop the transmission of the
infectious agent of an entire group or infectious disease in the community. There
community (and, in particular protection of are two, basic types of infectious disease
susceptible persons) as a result of a transmission: direct transmission and
substantial proportion of the population indirect transmission. Direct transmission
being immune to the agent. includes the immediate transfer of the
infectious pathogen to a susceptible host via
Outbreak: the occurrence of more cases of direct contact (e.g., touching someone) or
disease, injury, or other health condition spread by droplets (e.g., sneezing). Indirect
than expected in a given area or among a transmission includes the transfer of the
specific group of persons during a specific infectious pathogen to a susceptible host via
time-period. a vector (e.g., think a Desert Sand-fly
transmitting leishmaniasis to a susceptible
Epidemic: the occurrence of more cases of host) or an inanimate object (e.g., think of
disease, injury, or other health condition contaminated water coming in contact with
than expected in a given area or among a human skin and transmitting leptospirosis).
specific group of persons during a specific
time-period; the cases are presumed to have In order to stop the transmission of the
a common cause or to be related to one infectious disease in a community, the
another in some way. WHO has identified the systematic
approach used by field epidemiologists: [5]
Pandemic: an epidemic occurring over a
widespread area (multiple countries or Undertaking preliminary investigation
continents) and usually affecting a Identifying and notifying cases
substantial proportion of the population. Collecting data and analyzing data
Managing and controlling (including
Public health practice: refers to the community health education)
essential public health services of a public Disseminating findings and follow-up
health system.
In the terms presented above, the These main activities are designed to
reader will notice the quantitative aspect of identify the cause of a communicable
nearly all of the terms. Rates, proportions, disease and the best means to control it. A
and ratios are common types of calculations team of public health professionals (along
which applied epidemiologists or field with others) assist in an outbreak
epidemiologists encounter during their investigation.
practice. In public health practice, the public
health variables of interest are often
International Journal of Science and Healthcare Research (www.ijshr.com) 49
Vol.5; Issue: 2; April-June 2020GV Fant. Concepts of field epidemiology in preparation for response to infectious disease outbreak in rural
Rajasthan, India
Figure 1: “Chain of Infection” [13]
The “Chain of Infection” (Figure 1) over which persons are exposed, and the
is an important concept for the field minimum, average, and maximum
epidemiologist. [13] The “chain of infection” incubation periods of the disease in
is the progression of an infectious agent as it question. [13] There are four basic patterns
leaves its reservoir or host through a portal that can be seen in an “Epi Curve” (Figure
of exit, is conveyed by a mode of 2).
transmission, and then enters through an During the COVID-19 pandemic,
appropriate portal of entry to infect a the phrase “flattening the curve” has
susceptible host. An outbreak can be frequently been used. Basically, the phrase
stopped by breaking the “chain of infection” refers to how public health control methods
at any point. can be employed during an outbreak to
The incubation period and the period reduce the number of infectious cases. The
of communicability are the two “time reduction in the number of cases could
periods” often used to describe the natural occur because public health control methods
history of an infectious disease. The were, in fact, slowing the spread of the
“incubation period” is defined as the time infectious disease in a community. This
between initial contact with the infectious means that few people are developing the
agent and the development of clinical signs infection and, thereby, reducing demand on
of illness in and individual. The “period of the healthcare system for medical treatment
communicability” is defined as the time during the outbreak.
during which the infectious pathogen may Any software package can be used to
be transmitted to another susceptible host. construct an epidemic curve. For example,
The epidemic curve (or “Epi AcaStat (URL: www.acastat.com) is a low-
Curve”) is a histogram that shows the cases cost, easy-to-use statistical software
of an infectious disease during an outbreak package that can be used to construct an
in a specific area for a specific time period. “Epi Curve” (see Technical Box 1a and 1b).
The shape of the “Epi Curve” is determined Statistical software can support the
by the number of cases of the infectious quantitative efforts of epidemiologists.
disease in the community, the period of time
International Journal of Science and Healthcare Research (www.ijshr.com) 50
Vol.5; Issue: 2; April-June 2020GV Fant. Concepts of field epidemiology in preparation for response to infectious disease outbreak in rural
Rajasthan, India
Figure 2. Types of patterns found in epidemic curves (source: WHO 2008)
International Journal of Science and Healthcare Research (www.ijshr.com) 51
Vol.5; Issue: 2; April-June 2020GV Fant. Concepts of field epidemiology in preparation for response to infectious disease outbreak in rural
Rajasthan, India
The emergence of the infection in a detected regardless of the etiology, which is
community cannot be predicted, but most likely to be unknown. It requires
preparing for the possibility of an infectious skilled professionals to safely implement the
disease outbreak in a community is necessary countermeasures.
appropriate. An epidemic has phases as Phase 3-Control and Mitigation. Once the
described by the WHO: [14] infectious disease threat reaches an
Phase 1-Early Detection. Early detection epidemic or pandemic level, the goal of the
allows the rapid implementation of response is to mitigate its impact and
containment measures, which are the key to reduce its incidence, morbidity and
reducing the risk of amplification and mortality as well as disruptions to
potential international spread. Early economic, political, and social systems.
detection begins at the health care setting, Phase 4-Elimination or Eradication.
so health care workers must be trained to Elimination means that the disease is no
recognize potential epidemic disease, report longer considered as a major public health
quickly an unusual event (such as an issue. However, intervention measures
unusual cluster of cases or deaths). (surveillance and control) should continue
Phase 2-Containment. Effective and rapid to prevent its re-emergence. Eradication of
containment of emerging diseases is just as a disease – much more difficult and rarely
vital as early detection in order to avoid a achieved - involves the permanent
large scale epidemic. Rapid containment elimination of its incidence worldwide.
should start as soon as the first case is There is no longer a need for interventions
International Journal of Science and Healthcare Research (www.ijshr.com) 52
Vol.5; Issue: 2; April-June 2020GV Fant. Concepts of field epidemiology in preparation for response to infectious disease outbreak in rural
Rajasthan, India
measures. Three criteria need to be met in insecticide “to kill” malaria-carrying
order to eradicate a disease: there must be mosquitos; killing the eggs of the mosquito)
an available intervention to interrupt its Recall contaminated food products:
transmission; there must be available removing infected food from consumption
efficient diagnostic tools to detect cases that (e.g., food recalls)
could lead to transmission; and humans Isolate and quarantine hosts: isolation
must be the only reservoir. refers to separation of ill persons while
In the WHO document (including quarantine refers to the separation of a
the extended passage) previously cited, potentially exposed but well person (e.g.,
global public health professionals have keeping a sick child at home and not
expertly described the processes needed to permitting to go to school to infect others is
manage an epidemic. a form of isolation that prevents infecting
Section 3: Overview of Epidemiologic others)
Disease Control Methods Treatment and mass drug
Control of an infectious disease can be administration: treatment of the sick
achieved by “breaking the chain of persons to reduce period of
infection” to control the agent, to control communicability; mass drug administration
transmission, or to modify the environment. of the population with full dose of treatment
Several disease prevention and control drug against infectious disease (e.g., mass
measures are available to epidemiologists treatment of a population to control
and public health officials when confronted trachoma)
with an infectious disease in a community: Educate the public and providers:
[15-17]
teaching persons on what can be done to
Vaccinate: commonly used to refer to stop the infectious disease or prevent re-
procedures used to immunize (or vaccinate) occurrence (e.g., teaching community
against an infectious disease (e.g., MMR) members what they can do to prevent
Control environmental factors: malaria; notifying health professionals of an
environmental control measures that can be outbreak, case definition, reporting
used to disrupt the “chain of infection” (e.g., procedures, and clinical measures)
personal hygiene, use of clean water)
Control the agents or vectors of disease: These are examples of the disease control
actions taken “to kill” the agent or prevent methods that can be used to help stop an
the vector from reproducing (e.g., spraying outbreak.
Section 4: Team Approach to Outbreak Investigation and Emergency Response
Figure 3: Public Health Emergency Coordination and related activities for the successful management of an infectious disease outbreak
investigation and public health response. Adapted from: “Controlling Communicable Disease” by Norman Noah (Berkshire, England: Open
University Press, 2006)
International Journal of Science and Healthcare Research (www.ijshr.com) 53
Vol.5; Issue: 2; April-June 2020GV Fant. Concepts of field epidemiology in preparation for response to infectious disease outbreak in rural
Rajasthan, India
Finally, the field epidemiologist is ACKNOWLEDGEMENTS
part of a team of professionals working in a I appreciate the ongoing support
community to control or stop an infectious provided to me by the Jodhpur School of Public
disease outbreak. In Figure 3, we see the Health, Jodhpur, India, where I have been a pro-
basic categories of team activities necessary bono/volunteer faculty member since 2013. I am
grateful to AcaStat for allowing me to include
for organized response to a disease portions of their user manual in this manuscript
outbreak: epidemiological services; clinical to help me illustrate an epidemiologic point.
services; laboratory services; disease control
and health education; and public health Biographical Statement
emergency coordination. [18] In addition to Dr. GV Fant is a public health
highly advanced professional education, epidemiologist and visiting faculty member at
team-work, coordination, professionalism, JSPH, Rajasthan, India having taught subjects in
integrity, and collaboration are just some of epidemiology, biostatistics, field epidemiology,
the additional competencies necessary for and health database concepts to Indian MPH-
investigating an infectious disease outbreak degree students and public health professionals
in a population. since 2013. He is, also, the Executive Director
of the Society for Epidemiology at JSPH. Dr.
Fant earned his doctorate (PhD) from University
CONCLUSION of Nebraska in 1997. He earned two master’s
The study and practice of field degree- in the health sciences/public health and
epidemiology is exciting and meaningful. public administration. Dr. Fant earned
The key concepts of field epidemiology that professional recognition as an Epidemiologist
were discussed included: from the American College of Epidemiology
(MACE) in 2002, the Society for Epidemiology
Key terms at JSPH (MSEpi) in 2019, and as an
Outbreak investigation, the chain of International Practitioner of the Faculty of
infection, and related topics Public Health of the Royal Colleges of
Epidemic curve (including technical Physicians of the United Kingdom(IPFPH-UK)
in 2017. Beginning in 1997, Dr. Fant has served
details on making an “epi curve” with
as a U.S. civil servant and is an epidemiologist
software) in Northern Virginia, USA.
Epidemiologic disease control methods
Framework showing the team-work REFERENCES
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Vol.5; Issue: 2; April-June 2020GV Fant. Concepts of field epidemiology in preparation for response to infectious disease outbreak in rural
Rajasthan, India
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