1. Epidemiology is defined as the study of the distribution and determinants of health-related states or events in specified populations and the application of this study to control relevant health problems. 2. Key components of epidemiology include measuring disease frequency and distribution, and identifying determinants and risk factors of diseases. Infectious disease epidemiology studies topics such as infection, contamination, infestation, and the definitions of an infectious disease. 3. Epidemiology is useful for community diagnosis, disease surveillance, planning and evaluation of health programs, and identifying risk factors and the natural history of diseases.

1. Selected Definition in Infectious
Disease Epidemiology & Uses of
Epidemiology
Dr. Anuj Singh
MOH cum Asst. Professor
Community Medicnie
UIMS, Prayagraj

4. Epidemiology
• Epi = upon (among)
• Demos = people
• Ology = science

5. • Def:-
“The study of the occurrence and distribution
of health related events, states and process
in specified population, including the study of
the determinants influencing such process,
and the application of this knowledge to
control relevant health problems”

6. Components of Epidemiology
• Disease Frequency : The core characteristics of
epidemiology • are to measure the frequency of
diseases, disability or death
• Distribution of Diseases : Based on time, place &
person, epidemiology tenets help to identify if a
specific disease has increased or decreased in the
community
• Determinants of Diseases: To test hypothesis and
identifying the underlying causes (or risk factors) of
disease

8. Infectious Disease Epidemiology
• Selected Definition

9. INFECTION
• Entry and development or multiplication of
an infectious agent in an organism
• It implies body response to defend itself
against the invader
• An infection dose not always cause illness

10. •Several levels of infection-
1) Colonization: presence of a microorganism on/in a
host, with growth and multiplication of the
organism, but without interaction between host
and organism
Eg. S. aureus in skin and nasopharynx
2) Sub–clinical infection: Asymptomatic
3) Clinical Infection: Symptomatic
4) Latent infection: E.g. Herpes simplex virus

12. CONTAMINATION
• Presence of an infectious agent on a body
surface
• Contamination dose not implies Carrier State
• Pollution is district from contamination. It
implies presence of offensive but not
necessarily infectious content.

13. INFESTATION
• Lodgment, development and reproduction of
arthropod on the surface of body or in
clothing, e.g. lice, itch mite
• Infested articles or premises are those which
harbor or give shelter especially arthropods
and rodents

14. HOST
• Any living organism that becomes subsistence or
lodgment of an infectious agent.
I. Primary or definitive host: in which the parasite attains maturity
or passes its sexual stages
E.g. Female Anopheles mosquitoes
I. Secondary or intermediate host: in which parasite is in a larval or
asexual state
E.g. Humans (Malaria)
I. Obligate host: means the only host
E.g. Man in measles and typhoid (Viral diseases)
IV. Transport host: in which organism remains alive but dose not
undergo development

15. INFECTIOUS DISEASE
• A disease due to an infectious agent
• While some disease are contagious and others
are non contagious
E.g. COVID-19 & Food poisoning
• All infectious disease and infestation are
communicable disease

16. CONTAGIOUS DISEASE
• Diseases the is transmitted through close
contact
E.g.
STD
Scabies
Leprosy

17. COMMUNICABLE DISEASE
• An illness caused by an infectious agent or its
toxins through direct or indirect transmission
from an infected person or animal, or
reservoir to a susceptible host, either directly
or indirectly through an intermediate (host,
vector , environment)

18. EPIDEMIC
An unexpected increase in the number of
 disease cases
 specific health related event
 specific health related behavior
in a specific geographical area

19. ENDEMIC
• Constant presence of a disease or infectious agent in
specified geographic area or population
• Types-
1) Hyperendemic: disease is constantly at high incidence
and or prevalence rate and affects all age group
1) Holoendemic: High level of infection beginning early
in life and affecting most of the child population

20. PANDEMIC
• Epidemic occurring over a very wide area,
crossing international boundaries and usually
affecting large no of population

21. SPORADIC
• The cases occur irregularly, haphazardly from
time to time, and generally infrequently
• The cases are so few and separated widely
that they show little or no connection with
each other

23. EXOTIC
• Disease which are imported into a country in
which they do not otherwise occur

24. ZOONOSES
• An infection or infectious diseases transmitted
from vertebrate animal to man
A) Anthropozoonoses:
E.g. Rabieses, plague, anthrax
B) Zooanthroponoses: Infection transmitted from
man to animal E.g. Human tuberculosis in cattle
C) Amphizoonoses: Infection maintained both in
human and lower vertebrate animal. Infection in
either direction E.g. T. cruzi

25. EPIZOOTIC
• An outbreak of diseases in animal population
E.g. Anthrax, brucellosis, rabies, influenza
• Epizootiology: Study of epizootic disease

26. EPORNITHIC
• An outbreak of diseases in bird population

27. •ENZOOTIC
• An endemic occurring in animals
• E.g. Anthrax, rabiese, brucellosis, endemic
typhus and tick typhus

28. NOSOCOMIAL INFECTION
• Nosocomial (hospital acquired) infection is an
infection acquired by patent due to hospital
stay
• New disorder unrelated to patient primary
condition
• Infection acquired in the hospital but appear
after discharge
• E.g.UTI
HbsAg
Surgical wound infection

29. OPPORTUNISTIC INFECTION
• Infection with organism that are normally
commensals in human body but become
pathogenic when immune responses are
compromised
• E.g. AIDS
Steroid therapy

30. IATROGENIC DISEASE
• “Doctor-generated”
• Adverse effects of preventive, diagnostic,
therapeutic and other medical interventions
• E.g. Anaphylactic reaction (drug, vaccines)
HbsAg Infection
X-ray hazards

31. SURVEILLANCE
• Continuous scrutiny of the factors that
determine the occurrence and distribution of
disease and other condition of ill health
• By observing trends in time, place, person
change can be observed or anticipated for
appropriate action
• Through:
Morbidity, mortality reports,
Death certificates
Hospital records

32. ELIMINATION
• Reduction to “zero” incidence of a specified
disease in a defined geographical area
• Disease close to elimination
E.g. Polio, measles , diphtheria

33. ERADICATION
• Termination of all transmission of infection by
extermination of infectious agent
• Termination of infection from the whole world
• i.e. disease will no longer occur in the
population
• E.g. Small pox

35. Uses of epidemiology
1. To study historically the rise and fall of
disease in population
2. Community diagnosis
3. Planning and evaluation
4. Evaluation of individual’s risks and chances
5. Syndrome identification
6. Completing natural history of disease
7. Searching for causes and risks factors

36. 1. To Study Historically Rise and Fall
of Disease in the Population
• Health and disease pattern in community is
never constant. E.g. Smallpox rose, killed
millions and eradicated
• Epidemiology provides a means to study
disease profiles and time trends in human
population
• By study of these trends we can make useful
projections into the future and identify
emerging trends.

37. 1. To Study Historically Rise……Cont..
Studying ever changing disease pattern
Making future prediction
Giving early warning sign

38. 2. Community Diagnosis
 It refers to the identifications and quantification
of health problems in a community in terms of
mortality and morbidity rates and ratios
 Identification gives the purpose of defining
those individuals or groups at risk or those in need
of health care
Quantification
1) Lay down the priorities in disease control and
prevention
2) Source of new knowledge of disease
distribution, causation and prevention.

39. STEPS FOR COMMUNITY DIAGNOSIS
Step 1 - Establishing a Community Diagnosis
Step 2 - Analyzing the existing Health Data
Step 3 - Collecting Community Data
Step 4 - Combining existing Health Statistics with
community Data
Step 5 - Choosing Health Priorities
Step 6 - Developing the Community Health Action
Plan
Step 7 -Measuring Environmental and Policy
Changes
Step 8 -Creating the Community Diagnosis
Document

40. 3.Planning And Evaluation
• Planning is essential for rational allocation of
limited source
• Planning includes facilities for medical care
e.g.
1. No. of hospital beds required for specific
disease,
2. Health manpower planning for preventive
services
(e.g. Screening programmes, immunization)

41. 4. Evaluation of individual’s risks and
chances
• Epidemiologists calculate relative risk and
attributable risk for a factor related to or
believed to be a cause of disease.
• Eg. Smoking is risk factor for CHD, obesity for
diabetes

42. 5.Syndrome identification
• Till 1920 peptic ulcer was thought to be ingle
entity. Based on its large scale epidemic, data
and its analysis two entities duodenal and
peptic ulcer clearly distinguish.
• Recently obesity, dyslipidemia, HTN are risk
factor for CHD

43. 6.Completing natural history of disease
• Disease pattern in the community in relation to agent,
host, and environment.
• Eg. Natural history of atherosclerosis one third to two
third of deaths due to IHD are sudden ie. occur in less
than 1 hr.
• Hospital studies could never have come to this
conclusion, for most victims do not reach the hospital.
• Eg. The natural course of HIV and TB or any human
disease has been possible due to systematic
observations

44. 7.Searching for causes and risks factors
Eg.
• Congenital defect - Rubella
• Teratogenic effects - Thalidomide
• Smoking - Lung cancer