Surveillance involves the ongoing systematic collection and analysis of health data that is essential for public health planning and evaluation. There are different types of surveillance including active, passive, and sentinel surveillance. Disease occurrence can be endemic, epidemic, or pandemic depending on the usual levels and trends in a population. The demographic transition theory describes the stages a population goes through as it shifts from high birth and death rates to low birth and death rates as a country develops economically. This includes an early expanding phase with decreasing death rates, a late expanding phase as birth rates start to decline, and eventually a low stationary stage with balanced low birth and death rates.

1. SURVEILLANCE AND
LEVELS OF DISEASE OCCURRENCE,
DEMOGRAPHIC TRANSITION THEORY
Presented by: Sahar Soomro

2. SURVEILLANCE
• According the Centers for Disease Control and Prevention (CDC),
Epidemiological surveillance is “the ongoing systematic collection, analysis,
and interpretation of health data essential to the planning, implementation,
and evaluation of public health practice, closely integrated with the timely
dissemination of these data to those who need to know.”
• Mortality and Transmission Rates of Disease must be known in a population for
surveillance to Occur.

3. SURVEILLANCE
• Surveillance in general means to watch over carefully or to
observe any event.
• Surveillance in public health is the continuous, watching of
the incidence and distribution of health-related events
through systematic collection, analysis and interpretation of
data needed for the planning, implementation, and
evaluation of public health practice.
• It can be carried out to monitor changes in disease frequency
or to monitor changes in the levels of risk factors.
• Surveillance is systematic and ongoing process

4. CHARACTERISTICS OF IDEAL SURVEILLANCE
• An ideal surveillance should be:
• Simple
• Timely
• Representative
• Flexible
• Sensitive
• Strong predictive value
• Acceptable to
• The public
• Health care providers
• Cost-effective

5. IMPORTANCE OF SURVEILLANCE
• To assess the health status
• All the data collected are the reflection of health of people
• Keeps the record of existing health problems
• Helps in the interpretation of mortality and morbidity status
• To detect the change in the disease trend and health practices
• Continue recording of data notifies about the disease trend
• Keeps the track of disease
• Surveillance is also helpful for finding the natural history of disease.
• Collection of data for Planning, Monitoring and Evaluation
• The data required for PME is provided by surveillance
• It is the base for evidence-based policy formation
• Helps the program developer in priority setting
• Also helps in assessing the effectiveness of the interventions

6. IMPORTANCE OF SURVEILLANCE
• Early warning and detection of outbreaks
• Surveillance notifies about the disease
• All the data too helps in detecting the outbreaks
• Hence helps in preparedness
• To estimate the size of a health problem
• To detect epidemics or define a problem
• To facilitate emergency planning

7. TYPES OF SURVEILLANCE
1.) Active Surveillance
• Refers to active finding of the cases.
• Designated staffs review the records physically, visits the health facility, and confirms with
the health practitioner to find the particular cases.
• Often used for the disease which is at the verge of elimination and eradication and also in the
time of outbreak investigation.
• Requires more resources; as requires staff- healthcare professionals to visit hospitals
• Active Surveillance can be also used to check the validity of passive surveillance
• Reporting is usually more accurate here as it is performed by those specially assigned to
conduct this activity

8. TYPES OF SURVEILLANCE
• 2.) Passive Surveillance
• Surveillance in which the available data on diseases or conditions are used
• It refers to regular monitoring or reporting of the cases without active involvement in
identification/reporting by the health personnel
• Simple and very easy to carry out
• All institutions that provide health services to general people are the part of
this surveillance.
• They forward their records to the designated departments where all the reports are compiled
• Uniform format of reporting is followed
• Health management information system of government is an example of passive surveillance
• Inconsistency of recording can cause problem as things may not be taken seriously all the time

9. TYPES OF SURVEILLANCE
• 3.) Sentinel Surveillance
• It is a surveillance system which is used when the need of high quality data cannot be met
through passive surveillance
• It is a system where specific catchment area is selected for surveillance.
• Selection of sentinel surveillance site depends on possibility of high probability of cases/disease
• It deliberately involves limited network of carefully selected reporting sites.
Example: a network of large hospitals might be used to collect high-quality data on various
diseases
• Sites are selected on the basis of population flow, previous outbreak of disease, high presence of
risk group, etc.
• Sentinel Surveillance is not suitable for detecting rare disease
• This type of surveillance helps identify rapidly changing health condition of a specified disease
at a particularly specified time

10. STEPS OF SURVEILLANCE
• Reporting:
• Data has to be reported by the health worker, staffs , etc
• Data needs to be reported in pre-specified format
• Accumulation
• The reported data needs to be collected and compiled
• The data are collected in a designated departments
• Data collection follows the certain chain
• Data Analysis
• All the collected are then analyzed
• The data are converted in terms of rates, ratios, proportion, figures etc
• Interpretation and action
• Surveillance doesn’t stops in data collection
• Wise judgement needs to be made
• The information needs to be disseminated so that the further action are taken

11. LIMITATIONS OF SURVEILLANCE
• Surveillance depends upon the reporting so under-reporting
could be a problem.
• Inconsistency in reporting
• Reporting may not be representative
• Takes time for data collection, analysis and interpretation
• Surveillance is on the tool of epidemiology it is not the solution to
health problem.

13. SCREENING SURVEILLANCE
Gives a better idea of progress of disease from
sub clinical or covered to clinical or overt.
Gives a better idea for the prevention and control
of diseases
It is a part of secondary prevention It is a part of primary and tertiary prevention.
Has mass screening that indicates large-
screening of whole population groups.
Active surveillance has special searches for cases
limited to specific disease in intervals of time.
Selective screening refers to selected high risk
groups in a population.
Passive surveillance is for mainly long term
secular trends at one time.

14. SCREENING SURVEILLANCE
Multiple screening refers to combination of the
mass and selective screening.
Sentinel surveillance helps identify rapidly
changing health condition of a specified disease
at a certain time.
Used for Case detection, control of disease,
research, etc.
Used for mainly prevention and control.
Examples of screening tests include
mammography for breast cancer, pre-natal
amniocentesis for detecting congenital
malformations, or psychological tests to identify
early signs of cognitive decline.
Examples of surveillance includes Surveillance of
communicable disease, Non communicable
disease, Influenza, HIV/AIDS in Thailand, etc.

15. LEVEL OF DISEASE OCCURENCE
• ENDEMIC
The amount of a particular disease that is usually present in a community is referred to
as the baseline or endemic level of the disease.
• This level is not necessarily the desired level, which may in fact be zero, but rather is
the observed level.
• In the absence of intervention and assuming that the level is not high enough to
deplete the pool of susceptible persons, the disease may continue to occur at this level
indefinitely.
• Thus, the baseline level is often regarded as the expected level of the disease.

16. LEVEL OF DISEASE OCCURENCE
• Sporadic refers to a disease that occurs infrequently and irregularly.
• Endemic refers to the constant presence and/or usual prevalence of a
disease or infectious agent in a population within a geographic area.
• Hyperendemic refers to persistent, high levels of disease occurrence.
• Occasionally, the amount of disease in a community rises above the expected level.
• Epidemic refers to an increase, often sudden, in the number of cases of a disease above
what is normally expected in that population in that area.
• Outbreak carries the same definition of epidemic, but is often used for a more limited
geographic area.

17. LEVEL OF DISEASE OCCURENCE
• Cluster refers to an aggregation of cases grouped in place and time that are suspected to
be greater than the number expected, even though the expected number may not be known
• Pandemic refers to an epidemic that has spread over several countries or continents,
usually affecting a large number of people.
Epidemics occur when an agent and susceptible hosts are present in adequate numbers, and
the agent can be effectively conveyed from a source to the susceptible hosts. More specifically,
an epidemic may result from:
• A recent increase in amount or virulence of the agent,
• The recent introduction of the agent into a setting where it has not been before,
• An enhanced mode of transmission so that more susceptible persons are exposed,

18. EXAM QUESTION SAMPLE
1. _________22 cases of legionellosis occurred within 3 weeks
among residents of a particular neighborhood (usually 0 or 1
per year)
2. _____________Average annual incidence was 364 cases of
pulmonary tuberculosis per 100,000 population in one area,
compared with national average of 134 cases per 100,000
population
3. ________________Over 20 million people worldwide died from
influenza in 1918–1919
4. ________________Single case of histoplasmosis was diagnosed
in a community
5. ________________About 60 cases of gonorrhea are usually
reported in this region per week, slightly less than the
national average
A.Sporadic disease
B.Endemic disease
C.Hyper-endemic dx
D.Pandemic disease
E.Epidemic disease

19. ANSWERS TO SAMPLE EXAM QUESTIONS
1. E
2. C
3. D
4. A
5. B

20. DEMOGRAPHY TRANSITION THEORY

21. DEMOGRAPHIC TRANSITION THEORY
• The word ‘Demography’ came from the prefix ‘demo’ meaning people and ‘graphy’ meaning
description or measurement. Similarly, ‘transition’ means process of changing from one state
to another
• So, the phrase ‘Demographic Transition Theory’ clearly reflects from the name itself that it is
a theory/model which describes the population change that occurs over a period of time
• Demographic Transition is a gradual process in which a society moves from high birth rate
and death rate to low birth rate and death rate
• It deals with population change occurring from the past to the change that may occur in
future
• Furthermore, the theory shows the transition of population from high birth and death rate to
low birth and death rate as the country (or any region) moves from pre-industrial era to an
industrialized era. Thus the major emphasis of the theory is given to the economic
development which results in change in population
• The theory was 1st propounded and interpreted by an American demographer Warren
Thompson who saw changes in the population pattern all over the world in due course of

22. • It looks at three major indicators for assessing and predicting population change:
fertility, mortality and growth rate
• There are usually 4-5 stages for categorizing demographic transition. This is because
earlier categorization was done in 4 stages. However, with the change in population
pattern which could not be addressed by 4 stages, a new 5th stage has been added to it.
• This theory considering all 5 stages.
DEMOGRAPHIC TRANSITION THEORY

23. • The stage before industrial revolution. Also known as Pre-transition phase
• The country or region in this stage are characterized by high fertility (birth rate) and
high mortality (death rate)
• This stage has low or stable growth rate i.e. population remains constant due to high
birth and death rate
• Reasons for high birth rate were: lack of family planning methods, high infant
mortality rate convincing couples to have more babies, more family members = more
source of economic assets
• Reasons for high mortality rate were: poor health and health services, famine, lack of
proper education and unavailability of clean water and sanitation
• Relatively low people in older age
1. HIGH STATIONARY STAGE

25. 2. EARLY EXPANDING PHASE
• In this stage, birth rate keeps on increasing while death rates
begin to fall rapidly/sharply. This results in high/rapid population
growth
• It is also known as population explosion stage
• Reasons for decline in death rates were: increase in food supply
due to agricultural revolution and improvement in health and
sanitation causing reduction in child mortality
• High birth rate results in larger cohort of younger population
• Most of the least developed countries are in this stage

27. 3. LATE EXPANDING PHASE
• In this stage the birth rate also starts to fall/decrease
• However, the major point is that, while birth rate starts to decrease slowly
and gradually, death rate also keeps on falling slowly. This leads to the
narrowed gap between birth and death rate compared to early expanding
stage
• Result of this stage is low population growth or natural increase in
population
• Reasons for gradual decrease in birth rates were: the introduction of
contraceptive devices, increase in women’s status and rise in economic
conditions and education level of the people
• Most of the developing countries are in this stage

29. 4. LOW STATIONARY/ LOW FLUCTUATING STAGE
• It is known as the stage of stationary population
• In this stage, birth rates and death rates both are low. Also both of them
are approximately equal to each other
• This results in stability/slow rise in population--- STATIC population
• Most of the developed countries are in this stage

31. 5. DECLINING PHASE
• This stage is characterized by low death rate, lower birth rate and excess deaths over births
• In this stage birth rates are below death rates i.e. fertility rate is below the replacement
level (2 children). This leads to increase in elderly population compared to the younger
populations
• This stage is resulted due to continuous desire of the families to have a smaller family
• Some parts of Europe like Russia, Sweden and Germany and Japan are reaching towards
this stage