Epidemiology Public Health Dentistry Question And Answers

General Epidemiology

Question 1. What is epidemiology? Describe objectives and different types of epidemiological investigations.
Or
Define epidemiology. What are the aims and types of dental epidemiology?
Answer. Epidemiology is derived from Greek word epidemic. Epi means upon, Demos means people and Logos means science.

Definition of Epidemiology

Epidemiology is defined as “the study of the distribution and determinants of health-related status for events in specified populations, and the application of this study to the control of health problems.” John M Last (1988)

Aims or Objectives of Epidemiology

Three main aims of epidemiology were given by the International Epidemiological Association by Lowe & Kostrzewski (1973)

• To describe the size and distribution of disease problem in humans.
• To provide data essential for planning, implementation and evaluation of health services for the prevention, control and treatment of diseases and for setting up of priorities among those services.
• To identify etiological factors in pathogenesis of the disease.

Read And Learn More: Public Health Dentistry Question And Answers

Types of Epidemiological Investigations or Epidemiology

The science of epidemiology has three types or methods of study:

• Descriptive epidemiology
• Analytical epidemiology
  • Ecological study
  • Cross-sectional study
  • Case-control study
  • Cohort study.
• Experimental epidemiology
  • Randomized controlled trials
  • Field trials
  • Community trials.

Analytical Epidemiology

• Analytical studies are the second major type of epidemiological studies.
• The object is not to formulate but to test hypothesis.
• Analytical studies are of 2 types:
  • Case-control study
  • Cohort study

Case-Control Study

• Also called as retrospective study.
• A case control study involves two populations-one is case and another is control.
• In case-control study, the unit is the individual rather than the group.
• A case control study is basically a comparison study
• A case and control study has three distinct features:
  • Both exposure and outcome have occurred before the start of the study.
  • The study proceeds backward from effect to cause.
  • It uses a control or comparison group to support or refuse an inference.

Basic steps in controlling case-control study

• Selection of cases and control
  Selection of case can be done from:
  • Hospital
  • General population.
    Selection of control
  • Hospital control
  • Relatives
  • Neighbours control
  • General population.
• Matching: Matching is defined as a process by which you select control in such a way that they are similar to case with regard to certain selected variables, e.g. sex, age, etc.
• Measurement of exposure.
• Analysis and interpretation.

Analysis is done to find out

• Exposure rate among cases and control to suspected factors
• Estimation of disease risk associated with exposure.

Advantages of case-control study

• Relatively easy to carry-out
• Rapid and inexpensive
• Requires comparatively few subjects
• No risk to subject.
• No attrition problem
• Ethical problem is minimal.

Disadvantages of case-control study

• Problem of bias.
• Selection of appropriate control group may be difficult.
• We cannot measure incidence rate.

Experimental Epidemiology

• Experimental epidemiology is done under the direct control of investigator
• This is done to determine the effectiveness of a program of prevention or therapy.
• Experimental studies are of two types, i.e. randomized controlled trials and non-randomized or non-experimental trials.
• Randomized controlled trials are divided into clinical trials, preventive trials, risk factor trials, cessation experiments, trial of etiological agents and evaluation of health services.
• Examples of non-randomized controlled trials areuncontrolled trials, natural experiments and before and after comparison studies.

Experimental Epidemiology Advantages

• It provides scientific proof of etiological and predisposing factors so that prevention control and treatment can be made reliable and effective.
• It provides a method of measuring success and efficacy of health services.

Question 2. Write short note on incidence and prevalence.
Or
Write short note on prevalence.
Or
Write short answer on incidence and prevalence.
Answer. Disease frequency is measured by prevalence and incidence.

Prevalence

• Prevalence means the total number of cases (new and old) of a specific disease in existence in a given population at a certain period of time or at a point of time.
• “The total number of all individuals who have and attribute or disease at a particular time (or during a particular time period) divided by the population at risk of having the attribute or disease at this point in time or midway throughout the period” Last
• It is expressed as percentage of population and rangesfrom 0 to 100%.
• Therefore, it is of two types:
  • Point prevalence.
  • Period prevalence.

Point Prevalence

It is defined as total number of existing cases (new or old) of a specific disease during a defined period of time and is expressed in relation to defined population.Calculated as:

= \(\frac{\text { Total number of current cases at a given point of time }}{\text { Estimated population at the same point of time }} \times 100\)

Period Prevalence

It is defined as total number of existing cases (new and old) of a specific disease during a defined period of time and is expressed in relation to defined population.Calculated as:

= \(\frac{\begin{array}{c}
\text { Total number of existing case of a specific } \\
\text { disease during given period of time }
\end{array}}{\text { Estimated mid interval population at risk }} \times 100\)

Uses of Prevalence

• To estimate the magnitude and health/disease problem in the community.
• For planning and administration purposes.
• They identify the potential high-risk population

Incidence

Incidence rate is defined as the number of new cases occurring in a defined population during a specified period of time.

• Incidence rate is this number per specified unit of population.
• Incidence is expressed as the rate i.e. cases per population per time.
• Incidence ranges from zero to infinity.Calculated as:

Incidence = \(\frac{\begin{array}{c}
\text { Number of new cases of specific disease } \\
\text { during a given period of time }
\end{array}}{\text { Population at risk }} \times 1000\)

Uses of Incidence Rate

• To prevent and control disease
• It provides clue to research in etiology and pathogenesis
• To determine efficacy of preventive and therapeutic measures.
• It helps with study of distribution of disease.

Relationship Between Incidence and Prevalence

Prevalence depends upon two factors—the incidence and the duration of disease.

By assuming that if the population is stable and incidence and duration remain unchanged a relationship can be made out, which is:

Prevalence = Incidence × Mean Duration

Incidence = \(\frac{\text { Prevalence }}{\text { Duration }}\)

From the above relationship, the converse relationship is:

Incidence = \(\frac{\text { Prevalence }}{\text { Duration }}\)

Duration = \(\frac{\text { Prevalence }}{\text { Incidence }}\)

• So, from above equation it is clear that as the duration of disease increases greater is the prevalence.
• Changes in the prevalence from one time period to another time period, can result from changes in the incidence as well as changes in the duration of disease or both.

Question 3. Write short note on incidence.
Answer. Incidence is defined as the number of new casesoccurring in a defined population at a specified period of time.

Incidence can be calculated as:

Incidence = Number of new cases of a specific disease during a given time period/Population x 1000

• Incidence is expressed as the rate, i.e. cases per populationper time.
• It can range from zero to infinity.
• Incidence rate is the rate of occurrence of new casesarising in population conveniently expressed per unit time interval.

Types

There are two types of incidences:

• Episode incidence
• Cumulative incidence

Episode Incidence

It is the rate of occurrence of new episodes of the disease arising in population. This can be usually applied to conditions where previous reports may only be weakly reported.

Cumulative Incidence

It is similar to incidence but the time interval is expressed as the fixed period and result is expressed as proportion.

Uses of Incidence Rate

• To prevent and control disease
• It provides clue to research in etiology and pathogenesis
• To determine efficacy of preventive and therapeutic measures.
• It helps with study of distribution of disease.
  An increase in incidence rate of a disease is indicative of failure or ineffectiveness of the preventive or control program for that particular disease.

Question 4. Write note on descriptive epidemiology.
Or
Write in brief on descriptive epidemiology.
Or
Define epidemiology. Describe in detail descriptive epidemiology.
Or
Define epidemiology. Write in detail the steps of descriptive epidemiology.
Or
Define epidemiology. Explain in detail the descriptive epidemiology.
Answer.

Definition of Epidemiology

Epidemiology is defined as “the study of the distribution and determinants of health-related status for events in specified populations, and the application of this study to the control of health problems”. —John M Last (1988)

Descriptive Epidemiology

Descriptive epidemiology is usually the first phase of any epidemiological investigation.

• Descriptive epidemiology is concerned with observation of distribution of a disease or any health-related event in human population and identification of characteristics with which disease or condition is associated.
• It quantifies the disease status of the community.
• The various steps involved in descriptive study are as follows:
  • Defining the population to be studied
  • Defining the disease under study
  • Describing the disease by time, person and place
  • Measurement of disease
  • Comparing with known indices
  • Formation of an etiological hypothesis.

Defining the Population to be Studied

• First step in descriptive epidemiology study.
• The defined population can be the whole population in a geographic area or a representative sample taken from it.
• Defined population can also be a specially selected group such as age, sex group, school children, factory workers, hospital patients, etc.
• Defined population has to be stable without any migration.
• Most essential part of descriptive study is participation of people of community who are chosen for study.
• Other part is presence of healthy facility in close proximity to community which can serve the patients who require medical facilities.

Defining the Disease Under the Study

• Disease should be defined with operational definition in such a way so that it helps in identifying and measuring the disease in the defined population with accuracy.
• Type of definition is precise and valid for epidemiologist and helps to identify the people with disease from normal persons.
• Diagnostic methods used for the study should be applicable and acceptable by the population which it has to be studied.
• Operational definition gives the criteria by which the disease can be measured.
• While studying the diseases which do not show any sign or symptoms the epidemiologist should frame its own definition keeping in mind the objectives and accuracy of the study.

Describing the Disease by Time, Person and Place

The occurrence and distribution of a disease is described with well-accepted indices.

Time Distribution

There are three types of time fluctuations observed in occurrence of disease:

• Short-term fluctuation
  • Best example for short-term fluctuation is epidemics.
  • Three types of epidemics are:
    • Common source
      • Single exposure or point exposure: It is the response of group of persons to source of infection to which they are exposed, e.g. Food poisoning
      • Continuous or multiple exposure: In this, the exposure can be prolonged or continuous or repeated and need not to occur at same place or same time, e.g. well of contaminated water.
    • Propagated epidemics
      • Person to person: Transmission of infectious agent occurs from person to person, e.g. Hepatitis A. Speed of spread depends on herd immunity, opportunity for contact and secondary attack rate.
      • Arthropod vector:
      • Animal reservoir
    • Slow or modern epidemics

In modern epidemics, importance is given to excessive prevalence as the basic method of implication in epidemics.

• Periodic fluctuation
  • It is divided into seasonal trend and cyclic trend.
  • Seasonal trend: It is the important feature in infectious disease occurrence. e.g. GIT infections are seen in all summer while the upper respiratory tract infections are seen in winters.
  • Cyclic trend: Various diseases occur in cycles, i.e. they occur in short duration of time. e.g. measles occur in cycles in every 2 to 3 years.
• Long-term trends.
  • It means the change in disease which occurs in long duration of time.
  • Best example is oral cancer which increases during the duration of past 50 years, while diseases like typhoid and polio show downward trend.

Place Distribution

• By studying the distribution of the disease in different or same population in different or same country, we gain perspective on the variation in disease patterns.
• These variations may be classified as:
  • International variation: As per the descriptive studies pattern of occurrence of disease varies from country to country, e.g incidence of cancer varies from country to country
  • National variation: Variations among diseases are observed in the same country, e.g. Levels of fluoride are high in some regions and low in some regions in various parts of a country.
  • Rural-urban variation: Diseases varies in rural and urban populations, e.g. Cardiovascular diseases, drug addictions etc. seen in urban population while skin infections are more common in rural population.
  • Local distribution: Disease variation is also seen in cities or towns. They are best studied with the aid of ‘spot maps’ and ‘shaded maps’.

Person Distribution

• The disease is further characterized by defining the person who develops the disease by age, sex, occupation, habit, social class and other host factors.
• Various factors which are described in detail are:
  • Age: Age is more strongly related to the disease than any other single host factor. Various diseases are more frequent in certain age groups than in others, e.g. measles in childhood, cancer in middle age and atherosclerosis in old age.
  • Sex: Sex is another host characteristic. It has been found that various chronic diseases such as diabetes, hyperthyroidism and obesity are more common in women as compared to men while diseases such as coronary heart disease and lung cancer are prominent in men.
  • Ethnicity: Differences in disease occurrence are noted between population subgroups and different racial and ethnic origin. The diseases are tuberculosis, essential hypertension, coronary heart disease, cancer and sickle cell anemia.
  • Occupation: Persons working in particular occupations are exposed to various types of risks, i.e. workers in coal mines suffer from silicosis, sedentary workers face the risk of heart disease.
  • Marital status: Married persons have lower mortality rates as compared to unmarried. This is because married persons are more healthier, secure and protected. Marital status can be a risk factor for certain diseases such as cancer of cervix which is rare among the nuns which remain unmarried.

Measurement of Disease

• Measurement of disease shows the amount of disease or disease load present in the community.
• Disease is measured in terms of mortality, morbidity, disability, etc.
• Measurement of mortality is straight forward
• Morbidity has two aspects, i.e. incidence and prevalence.
• Incidence is obtained from longitudinal studies and prevalence from cross-sectional studies.
• Descriptive epidemiology uses a cross-sectional or longitudinal design to obtain estimates of magnitude of health and disease problem in human population.
• Cross-sectional study or prevalence study is a simple form of observational study.
• Cross-sectional study is based on single examination of a cross-section of population in one point of time.
• Longitudinal studies are the cross-sectional studies which are carried out for a longer duration by repeating periodically.
• In longitudinal studies, same individuals are examined on repeated periods.

Comparison with Known Indices

• By comparing the results with the similar studies on different groups of the population and subgroups of same population, it is possible to arrive at a clue to disease etiology.
• Identification of groups can be done which are at increased risk for various diseases.

Formulation of Hypothesis

• It is the final step of descriptive epidemiology.
• A hypothesis is a supposition, arrived at from observation or reflection.
• An epidemiological hypothesis should specify the following:
  • The population: Characteristics of persons to whom hypothesis is applied.
  • The specific cause being considered
  • Expected outcome-the disease
  • Dose-response relationship: Amount of cause needed to lead to a stated incidence of effect.
  • Time-response relationship: Time period that will elapse between exposure to cause and observation of effect.

Question 5. Write short note on case-control and cohort studies.
Answer. Analytical epidemiology comprises two types of observational studies, i.e. case-control study and cohort study.

Case-Control Study

• It is also known as retrospective study.
• It is the first approach to test casual hypothesis
• A case control study consists of two populations, i.e. cases and controls.
• In case control study the unit is an individual.
• These studies are the comparison studies.
• A case and control study has three distinct features:
  • Both exposure and outcome have occurred before the start of the study.
  • The study proceeds backward from effect to cause.
  • It uses a control or comparison group to support or refuse an inference.
• There are four basic steps required for conducting a case control study, i.e.
  • Selection of cases and controls
  • Matching
  • Measurement of exposure
  • Analysis and interpretation

Cohort Study

Cohort study is an observational study.

• It attempts to study the relationship between a purported cause and the subsequent risk of developing disease.
• It is known by a variety of names, prospective study, longitudinal study, incidence study and forward-looking study.
• Cohort: Defined as the group of population who share a common characteristics or experiences within as defined time period, e.g. age, occupation, exposure to the drug or vaccine.

Types of Cohort Study

• Prospective cohort study: It is a longitudinal follow-up of cases or population over a period of time.
• Retrospective cohort study: It is a longitudinal study in profile of a sample of population.
• Combination of retrospective and prospective studies.

Elements in Cohort Study

• Selection of study subjects:
  • They are usually assembled either from general population or select group of the population.
• Obtaining data on exposure:
  • Information about exposure may be obtaining directly from cohort members, review of records, medical examination or special tests.
• Selection of comparison group:
  • Internal comparison: No out side group is required.
  • External comparison.
  • Comparison with general population rate.
• Follow-up:
  • At the start of study, method should be devised depending upon the outcome to obtain data assessing the outcome.
• Analysis:
  • The data is analysed in term of:
    • Incidence rate of outcome.
    • Estimation of risk.

Case-Control Study Advantages

• It is analytical (Observational) study.
• It allows an investigator to examine a large number of hypotheses at one time.
• The temporal sequence of cause and effect may be clearly seen.

Case-Control Study Disadvantages

• Time required is long for data to generate.
• Very expensive.
• Sample has to be large to ensure adequate sample size after attrition.

Question 6. Write in brief differences between case control and cohort studies.
Or
Define epidemiology. Discuss difference between case control and cohort studies.
Answer.

Question 7. Write short note on experimental epidemiology.
Or
Define epidemiology and discuss in detail about experimental Epidemiology.
Answer.

Experimental Epidemiology

Experimental epidemiology means the study of epidemics among colonies of experimental animals such as rats.

• These studies are under the direct control of investigator.
• Experimental studies involve some action, intervention, manipulation such as deliberate application or withdrawal of suspected cause or changing one variable in causative chain in experimental group while making no change in control group and observing as well as comparing outcome of experiment in both groups.

Aims of Experimental Epidemiology

• To provide “scientific proof” of risk factors which may permits the modification or control of those diseases.
• To provide a method of measuring effectiveness and efficacy of health services for prevention, control and treatment of disease and improve health of community.

Types of Experimental Studies

Experimental studies are of two types, i.e.

• Randomized controlled trials
• Nonrandomized or nonexperimental trials.

Nonrandomized Trials

• Although the experimental method is always preferred, it is not always possible for ethical, administrative and other reasons to resort a randomized control trial in human beings.
• Some preventive measures are applied only to groups on a community wide basis.
• When disease frequency is low and natural history is long randomized control trials require follow-up of thousands of people for a decade or more.
• In such situation one has to depend on other study designs which are known as nonrandomized trials.
• Examples of nonrandomized controlled trials are uncontrolled trials, natural experiments and before and after comparison studies.

Question 8. Write short note on Randomized Controlled Trial(RCT).
Or
Write short note on RCT Trial.
Answer. Randomized Controlled Trials (RCT) are the experimental studies which involves the process of random allocation.

The basic steps in conducting a RCT include:

• Drawing up a protocol
• Selecting reference and experimental populations
• Randomization
• Manipulation or intervention
• Follow-up
• Assessment of outcome

Drawing up a Protocol

Protocol specifies the aims and objectives of study, criteria to select the study and control groups, size of the sample, procedures for allocation of subjects in the study and control groups, treatments to be done, standardization of working procedures and schedules, up to the stage of evaluation of outcome of the study.

As protocol has been established, it should be strictly adhered throughout the study.

Selecting Reference and Experimental Populations

• Reference or target population: It is the population in which findings of the trial, if found successful, is expected to be applicable. A reference population may be as broad as mankind or it may be geographically limited or limited to persons in specific age, sex or social groups.
• Experimental or study population: It is derived from the reference population. It is the actual population which participates in the experimental study. Ideally, it should be randomly chosen from the reference population, so that it has the same characteristics as the reference population. When an experimental population has been defined, its members are invited to participate in the study.
  The participants or volunteers must fulfill the following three criteria:
  • They must give “informed consent”, i.e. participants must agree to participate in the trial after having been fully informed about the purpose, procedures and possible dangers of the trial.
  • They should be representative of the population to which they belong.
  • They should be qualified or eligible for the trial.

Randomization

In randomization participants are allocated into the study groups and control groups at random. Randomization eliminates the “bias” and form groups which allows for comparability. Random allocation provides every individual gets an equal chance of being allocated into either group. Randomization is best done using a table of random numbers.

Manipulation

In this step, the investigator intervenes or manipulates the study group by deliberate application or withdrawal or reduction of the suspected control factor. The control group may have a standard intervention, a placebo or no intervention at all.

Follow-up

In follow-up examination of the experimental and control group subjects is done at defined intervals of time, in a standard manner under the same given circumstances till final assessment of outcome. Some losses to follow-up are inevitable due to factors such as death, migration and loss of interest. This is known as attrition.

Assessment

The final step in assessing the outcome of the trial is in terms of:

• Positive results: It represents benefits of experimental measure such as reduced incidence or severity of the disease.
• Negative results: It represents severity and frequency of side-effects and complications including death.

Question 9. Write short note on blinding.
Answer. Randomization cannot guard against the bias nor the size of sample. To reduce these problems blinding is carried out. Blinding ensures that the outcome is assessed objectively.

Blinding is done in three ways, i.e.

• Single blind trial
• Double blind trial
• Triple blind trial

Single Blind Trial

It is so planned that the participant is not aware whether he belongs to the study group or control group.

Double Blind Trial

It is so planned that neither the doctor nor the participant is aware of the group allocation and the treatment received.

Triple Blind Trial

In this the participant, the investigator and the person analyzing the data are all “blind”.

Ideally triple blinding should be used but double blinding is most frequently used method when as blind trial is carried out.

Question 10. Write short note on clinical trials.
Answer. Clinical trials are concerned with evaluating therapeutic agents mainly drugs.

• All the clinical trials are not susceptible for blinding. For example, there is no way to perform clinical trial of disimpaction without being obvious who receive surgery and who had not received the surgery.
• Various ethical, administrative and technical problems are involved in conduct of clinical trial.

Phases of Clinical Trial

Following are the phases of clinical trials:

Phase 0

• It is also known as human microdosing studies.
• It is a recent design for exploratory, first in human trial.
• The phase was designed for speeding up the development of promising drugs by establishing that the drug behave on human subjects.
• This phase does not provide any data on safety or efficacy.
• Drug manufacturing companies carries out phase 0 studies for ranking drugs in order to decide which drug has best pharmacokinetic parameter in human to take forward its further development.

Phase 1

• It is the first stage of testing in humans.
• For this, a group of 20 to 100 healthy persons are selected.
• Phase 1 assesses the safety, tolerability, pharmacokinetics and pharmacodynamics of a drug.
• Such trial is conducted in a clinical trial clinic wheresubject occupy research bed and is under observation of full time staff.
• This phase is of short duration.
• Volunteer involved in this phase should be paid an inconvenient fee for the time spent in volunteer center depending on time of participation.

Phase 2

• This phase assess the effectiveness of the drug or device to determine its appropriate dosage and for investigation of its safety.
• It is performed on larger groups, i.e. 100 to 300 persons.
• This phase is used to continue Phase I safety assessment in large groups.
• It is subdivided into two groups, i.e.
  • Phase 2A: It is design to assess dosage requirements
  • Phase 2B: It is design to assess efficacy of drug.

Phase 3

• These are randomized controlled multicentric trials on large group of patients, i.e. 300 to 3000.
• The phase is aimed for definite assessment of how effective the drug is when comparison is done with current ‘gold standard’ treatment.
• This phase is most expensive and time consuming.
• As the drug is passed in this phase the results are combinedin the large document which consists of comprehensive description of methods and result of human and animal studies, manufacturing procedure and shelf life.
• Drugs which undergo this phase come under FDA norms.
• Results from this phase are used by regulatory agencies for evaluating that a new product is licensed for general public use.

Phase 4

• It is also called as postmarketing surveillance trial.
• It involves safety surveillance and ongoing technical support of a drug after it receives permission to sold.
• This phase is required by regulatory authorities or sponsoring company for competitive reasons.

Phase 5

This is used to signify integration of new clinical treatment into widespread public health practice.

Question 11. Define epidemiology and uses of epidemiology and give its practical applications in relation to dental patients.
Answer. Epidemiology is defined as “the study of distribution and determinants of health related states or events in specified populations and the applications of this study to the control of health problems”. John M Last (1988)

Uses

In Community Diagnosis

An epidemiologist makes the diagnosis of a health problem faced by the community. Community diagnosis includes identification of the problem and its description in terms of place, person and time. Community diagnosis helps the administrators and policy and makers in deciding the appropriate strategy for prevention and control of the problem.

Rise and Fall of Disease

In epidemiology, study of time distribution and trends of various diseases provides an insight into its etiology. Example is occurrence of a large number of cases over a short period of time in a limited area indicates an epidemics. Study of time trends also helps in making projections about disease and requirement of resources in future.

Planning and Evaluation

Epidemiology helps the health administrator in prioritization of various problems. The information from the community diagnosis helps in planning of the health care administration. For example, information on person distribution—helps in identifying ‘at risk groups’; information on place distribution helps in identifying the vulnerable areas; information on the time distribution—helps in deciding appropriate time for initiation of preventive and control measures. Evaluation of preventive and control measures is required to see that the measures are giving adequate returns.

Evaluation of Individuals Risk

Epidemiological studies give an estimate of individual risk of a particular disease. Many of the indices like odds ratio, relative risk, attributable risk, etc. have been described to quantify the risk of individual or group. Multivariate analysis can help in estimating the risk of an unfavorable outcome with combination of risk factors.

Syndrome Identification

Epidemiological studies help in identifying the association between two characteristics. Many genetic disorders like Down’s syndrome have been identified initially through epidemiological studies only. Epidemiological studies give a clue to the different etiological nature of apparently similarconditions viz. bimodal age distribution in case of Hodgkin’s disease and diabetes mellitus.

Search for Causes/ Risk Factors

The study of distribution of disease, association and correlation between the different characteristics and various experimental studies give clues to etiology of diseases.

Completing the Natural History of Disease

An epidemiologist can appreciate and study the entire spectrum of disease. Epidemiology can study the phenomenon like carriers, sub-clinical cases, asymptomatic cases and many important aspects of chronic diseases.

Practical Application of Epidemiology in Relation to Dental Patients

• New concepts in relation to the epidemiology and management of periodontal disease suggest that there needs to be a rethink in relation to the provision of care. The efficacy of scaling and polishing and calculus removal has been questioned. Periodontal disease does not appear to have a significant impact on oral health. There is a strong association between plaque and tobacco use in the etiology of periodontal disease.
• The incidence of dental caries is continuing to drop butthere are indications that this decline may have slowed in 5-year-olds. Epidemiological studies demonstrate a reduction in provision of restorative care for children. Adults are retaining more natural teeth into later life. This has implications for the maintenance of their dentition.
• There is evidence that new concept in diagnosis and management of dental caries has not penetrated clinical practice. However, the development of adhesive materials has the potential to stimulate a noninvasive approach to the management of early carious lesions. Epidemiological studies suggests that decline in dental caries have been attributed to widespread use of fluoridated toothpastes. There is potential for further declines by reducing sugar consumption and appropriate exposure to fluorides and appropriate use of fissure sealants.
• Malocclusion does not contribute to poor oral health; its impact lie in the social and psychological domains of health. The decision to seek orthodontic care is complex and there is evidence that dentists are often the instigators of a need not previously felt by the patient. A review of the provision of orthodontic care in the General Dental Service demonstrated that 21% of cases were unimproved or worse as a result of orthodontic treatment.
• Erosion and tooth surface loss has been linked with the consumption of demineralizing food and drinks. It appears to have low prevalence at present but will need to be monitored over the next few years.

Question 12. Give step by step description of scientific pattern of an epidemiological investigation.
Answer. Following is the step by step description of scientific pattern of an epidemiological investigation:

Verification of Diagnosis

• Verification of diagnosis is the first step in an epidemiological investigation.
• It may happen sometimes that the report can arise from misinterpretation of signs and symptoms by the lay public.
• It is therefore necessary to have the verification of diagnosis on the spot, as quickly as possible.
  • A clinical examination of a sample of cases is carried out.
  • Laboratory investigations wherever applicable, are most useful to confirm the diagnosis but the epidemiological investigations should not be delayed until the laboratory results are available.

Confirmation of the Existence of an Epidemic

• Next step is to confirm if epidemic exists.
• This is done by comparing the disease frequencies during the same period of previous years.
• An epidemic is said to exist when the number of cases are in excess of the expected frequency for that population, based on past experience.
• An arbitrary limit of two standard errors from the endemic occurrence is used to define the epidemic threshold for common diseases.
• Often the existence of an epidemic is obvious needing no such comparison, as in the case of common source epidemics, e.g. cholera. These epidemics are easily recognized.
• In contrast the existence of modern epidemics is not easily recognized unless comparison is made with previous experience.

Defining the Population At-risk

Obtaining a map of the area:

• Before beginning the investigation, it is necessary to have a detailed and current map of the area.
• If map is not available, it may be necessary to prepare such a map.
• Map should contain information concerning natural landmarks, roads and the location of all houses along each road or in isolated areas.
• Area may be divided into segments, using natural landmarks as boundaries. This may again be divided into smaller sections. Within each section, the dwelling units, i.e. houses may be designated by numbers.

Counting the population:

• Denominator may be related to the entire population or sub-groups of a population.
• It may also be related to total events.
• For example, if the denominator is the entirepopulation a complete census of the population by age and sex should be carried out in the defined area by house-to-house visits.
• For these visits, health workers in sufficient numbers may be employed.
• By this technique it is possible to establish the size of the population.
• Population census will help in computing the much needed attack rates in various groups and subgroups of the population later on. Without an appropriate denominator of “population at risk” attack rates cannot be calculated.

Rapid Search for all Cases and their Characteristics

Medical survey:

• A medical survey should be done in the defined area to identify all cases including those who have not got medical care, and those possibly exposed to risk.
• Ideally, the complete survey will pick up all affected individuals with symptoms or signs of the disorder.
• Employed health workers may be trained to administer the “epidemiological case sheet” or questionnaire to collect relevant data.

Epidemiological case sheet:

• Epidemiologist should be armed with an “epidemiological case sheet” for collecting data from cases and from persons apparently exposed but unaffected.
• The epidemiological case sheet or “case interview form” should be carefully designed to collect relevant information.
• It includes name, age, sex, occupation, social class,travel, history of previous exposure, time of onset of disease, signs and symptoms of illness, personal contacts at home, work, school and other places; special events such as parties attended, foods eaten and exposure to common vehicles such as water, food and milk; visits out of the community, history of receiving injections or blood products, attendance at large gathering, etc.
• Information collected should be relevant to the disease under study. For example, if the disease is food-borne, detailed food histories are necessary.
• A case review form will ensure completeness and consistency of data collection.
• If the epidemic is large, it may not be possible to interview all the cases. In such cases, a random sample should be examined and data is collected.

Searching for more cases :

• Patient may be asked if he knew of other cases in the home, family, neighborhood, school, work place having an onset within the incubation of the index case.
• Cases admitted to the local hospitals should also be taken into consideration. This may reveal not only additional cases but also person-to-person spread.
• The search for new cases (secondary cases) should be carried out everyday, till the area is declared free of epidemic.
• This period is usually taken as twice the incubation period of the disease since the occurrence of last case.

Data Analysis

• Data collected should be analyzed on ongoing basis, using the classical epidemiological parameters, i.e. time, place and person.
• If the disease agent is known, the characteristics of time, place and person may be rearranged into Agent-Host Environment model.
  • Time: Prepare a chronological distribution of dates of onset and construct an “epidemic curve”. Look for time clustering of cases. An epidemic curve may suggest:
    • Time relationship with exposure to a suspected source
    • Whether it is a common source or propagated epidemic
    • Whether it is a seasonal or cyclic pattern suggestive of a particular infection.
  • Place: Prepare a “spot map” of cases, and if possible, their relation to possible sources of infection, e.g., water supply, air pollution, etc. Clustering of cases may indicate a common source of infection. Analysis of geographic distribution may provide evidence of the source of disease and its mode of spread.
  • Person: Analyze the data by age, sex, occupation and other possible risk factors. Determine the attack rates/case fatality rates, for those exposed and those not exposed and according to host factors. For example, in most food-borne outbreaks, food-specific attack rates must be calculated for each food eaten to determine the source of infection. Purpose of data analysis is to identify common event or experience, and to delineate the group involved in the common experience.

Formulation of Hypothesis

On the basis of time, place and person distribution or the Agent Host-Environment model, formulate hypothesis to explain the epidemic in terms of (a) possible source (b) causative agent (c) possible modes of spread, and (d) the environmental factors which enabled it to occur. These hypothesis should be placed in order of relative likelihood. Formulation of a tentative hypothesis should guide further investigation.

Testing of Hypothesis

• All reasonable hypothesis need to be considered and weighed by comparing the attack rates in various groups for those exposed and those not exposed to each suspected factor.
• This will lead the epidemiologist to ascertain whichhypothesis is consistent with all the known facts.
• When divergent theories are presented, it is not easy to distinguish immediately between those which are sound and those which are merely plausible.
• Therefore it is instructive to turn back to arguments which have been tested by the subsequent course of events.

Evaluation of Ecological Factors

• An investigation of the circumstances involved should be carried out to undertake appropriate measures to prevent further transmission of the disease.
• Ecological factors which have made the epidemic possible should be investigated such as sanitary status of eating establishments, water and milk supply; breakdown in the water supply system; movements of the human population, atmospheric changes such as temperature, humidity and air pollution, population dynamics of insects and animal reservoirs.
• The outbreak can be studied in a case control fashion.
• One of the primary concerns of the epidemiologist is to relate the disease to environmental factors to know the source of infection, reservoirs and modes of transmission.

Further Investigation of Population at Risk

• A study of the population at risk or a sample of it may be needed to obtain additional information.
• This can involve medical examination, screening tests, examination of suspected food, feces or blood samples, biochemical studies, assessment of immunity status, etc.
• The approach may be retrospective or prospective.
• Healthy individuals from the same universe may be studied in a case control fashion.
• This will permit classification of all members as to:
  • Exposure to specific potential vehicles.
  • Whether ill or not.

Writing the Report

• The report should be complete and convincing.
• Information to be included in the final report on anepidemic is given.

Question 13. Write short note on population explosion.
Answer. Population explosion occurs if the number of people in a group exceeds the carrying capacity of a region occupied by that group.

• Population explosion can further be viewed, in a longterm perspective, as existing when a population can’t be maintained without the rapid depletion of nonrenewable resources or without degradation of the capacity of environment to give support to the population.
• Overpopulation can result from an increase in births, a decline in mortality rates, an increase in immigration, or an unsustainable biome and depletion of resources. It is possible for very sparsely populated areas to be overpopulated if the area has a meager or nonexistent capability to sustain life (e.g., a desert).
• Population explosion is due to the following major reasons:
  • Increase in birth rates due to medical improvements
  • Decrease in death rates due to better medical facilities and advancements in the field of medicine.
  • Immigration to better developed countries due to several reasons like better job opportunities, war, and natural causes like hurricanes, earthquakes, and so forth.

Question 14. Define epidemiology. Enumerate the principle of epidemiology. Differentiate case control Vs cohort studies.
Answer.

Principles of Epidemiology

Following are the principles of epidemiology:

• Exact observation (Strict, vigorous, accurate, precise)
• Correct interpretation (Free from error)
• Rational explanation (Intelligent, sensible, reasonable)
• Scientific construction (By expert knowledge and technical skill)

Question 15. Write short note on Odd’s ratio.
Answer. Odd’s ratio is also known as cross-product ratio.

• Odd’s ratio is derived from the case control study and is the key parameter in analysis of case control studies.
• Odd’s ratio is the measure of strength of association between risk factor and outcome.
• Odd’s ratio is closely related to relative risk.
• Derivation of Odd’s ratio is based on three assumptions, i.e.
  • Disease investigated should be relatively rare. Majority of chronic diseases have low incidence inside the general population
  • Cases should be representative of those with disease.
  • Controls should be representative of those without disease.

Odd’s ratio is mainly the cross-product of entries, i.e.

Odd’s ratio = ad/bc

Odd’s ratio = ad/bc = \(\frac{33 \times 27}{55 \times 2}=8.1\)

In above example, smokers of less than 5 cigarettes daily showed a risk of developing lung cancer 8.1 times than who don’t smoke tobacco.