COMMUNITY MEDICINE DR. ZAKIRHUSAIN SHAIKH Concept of Health and Disease Definition of Health (WHO-1948) Health is a state of complete physical, mental and social wellbeing and not merely an absence of disease or infirmity (which enables one to lead to socially and economically productive life)

Primary healthcare Essential healthcare based on practical, scientifically sound and socially acceptable methods and technology, made universally accessible to individuals and families in the community through their full participation and at a cost that the country and community can afford to maintain at every stage of their development in the spirit of self-determination.

Elements of primary healthcare 1. Education regarding prevailing health problems and the methods of preventing and controlling them 2. Prevention and control of locally endemic diseases 3. Provision of essential drugs 4. Maternal and child health care and family planning 5. Immunization against major infectious diseases 6. Promotion of food supply and proper nutrition 7. Appropriate treatment of common diseases and injuries 8. An adequate supply of safe water and basic sanitation

Principles of primary healthcare • Equitable distribution • Community participation • Appropriate technology • Inter-sectorial coordination

Indicators of Health

• Mortality Indicators • Morbidity Indicators • Disability Indicators • Quality of Life Indicators Mortality Indicators

Crude death Rate: It is defined as the number of deaths from all causes per 1000 estimated mid-year population in one year in a given population

India- 6.4 Case fatality rate

• It is total number of deaths due to a particular disease per 100 cases of the same disease. • It represents the killing power of the disease • The time interval is not specified • It is used in acute infectious diseases • It is expressed in percentage Proportional mortality rate

• Proportion of all the deaths attributed to a particular disease of all the deaths by all the causes. • It helps in estimating the burden of a disease in the community International Death certificate

• Part Ia- disease or condition directly leading to death • Part Ib and Ic- morbid condition, if any giving rise to the above cause, stating the underlying condition last • Part-II-other significant conditions, contributing to the death, but not related to the disease or condition causing it

• In case of both births and deaths, registration has to be done within 21 days Incidence & Prevalence Incidence: Number of new cases occurring in a defined population during specified period of time usually expressed per 1000 population Prevalence: All the cases, current and old existing at a given point in time or over a period of time in a given population.

Secondary Attack rate

• It is the number of exposed persons developing a disease during the incubation period following exposure to a primary case

Physical Quality of Life Index

• Infant mortality rate • Life expectancy at age 1 • Adult literacy • Score from 0-100

Sullivan’s index

• Expectation of life free of disability, computed by subtracting from the life expectancy the probable duration of bed disability and inability to perform major activities. • Sullivan’s Index = Life expectancy – YLD (years lived with disability)

Disability Adjusted Life Years

• Expresses years lost to premature death and years lived with disability adjusted for the severity of the disability. • One DALY is one lost year of healthy life • DALY= YLD + YLL

Human development index

• India’s HDI score- 0.624 • India’s Rank -131 • Medium development category Human poverty index • HPI-1 (for developing countries) • Long and healthy life- • Vulnerability to death at early age- probability at birth of not surviving to age 40 years Knowledge- • Illiteracy- adult literacy rate Standard of living- • % of population not using an improved water source • % of children underweight for age

Levels of prevention

Impairment – Disability - Handicap

• Impairment: Any loss or abnormality of psychological, physiological or anatomical structure or function. • Disability: Any restriction or lack of ability to perform an activity in the manner or within the range considered normal for the human being. • Handicap: Any restriction or lack of ability to perform an activity in the manner or within the range considered normal for the human being.

Standardized rates

• Due to differences in age composition, crude rates are not comparable among populations. To make them comparable, age standardization is done. • It is done by two methods- direct and indirect standardization. • Direct Standardization - This can be used only when actual specific rates in subgroups of the observed population are available, along with the number of individuals in each subgroup

MCQ The following is true about prevalence and incidence (AIIMS 2003, 2005) a)Both are rates b)Prevalence is a rate but incidence is not c)Incidence is a rate but prevalence is not d)Both are not rates Rate- it measures the occurrence of a particular event in a specified population during a given period of time. • The numerator is a component of the denominator • Rate measures the incidence Ratio- it expresses the relation in size between two random quantities • The numerator is not a component of the denominator Proportion- it expresses the relation in size of a part of the whole. • The numerator is always included in the denominator • Proportion measures the prevalence

The rate adjusted to allow for the age distribution of the population is (AIIMS 2003, 2005) a)Perinatal mortality rate b)Crude mortality rate c)Fertility rate d)Age-standardized mortality rate A one-day census of inpatients in a mental hospital could- (AIIMS 2005) a)Give good information about the patients in that hospital at that time b)Give reliable estimates of seasonal factors in admissions c)Enable us to draw conclusions about the mental hospitals in India d)Enable us to estimate the distribution of different diagnosis in mental illnesses in the local area If the prevalence is very low as compared to the incidence of the diseases, it implies- (AIIMS 2005) a)Disease is very fatal and and/or easily curable b)Disease is not fatal c)Calculation of prevalence and incidence is wrong d)Nothing can be said, as they are independent Vitamin A prophylaxis is (AIIMS 2010) a)Specific protection b)Health promotion c)Secondary d)Primordial HPI includes all except (AIIMS 2013) a)Probability at birth of not surviving till age 40 b)Child literacy rate c)% Of population not using an improved water source d)% Of children underweight for age

Which of the following is example of disability limitation (AIIMS 2008) a)Reducing the occurrence of polio by immunization b)Arranging for schooling of child suffering from PRPP c)Resting affected limb in neutral position d)Providing calipers for walking All the statements are true about standardization except- (AIPGME 2006) a)Standardization allows comparison to be made between two different populations b)The national population is always taken as the standard population c)For direct standardization, age specific rates of the study population are applied to that of the standard population d)For indirect standardization age specific rates of the standard population are applied to the study population The denominator for calculating proportional mortality rate from a specific disease is: (UPSC CMS 2015) a)Mid-year population during that year b)Population at risk in that particular area c)Total deaths in that year d)Attributable deaths of a particular disease What is the time limit for registration of a birth? (UPSC CMS 2014) a) 7 days b) 14 days c) 21 days d) 3 days A village has a total of 100 under-five children. The coverage with measles vaccine in these age groups is 60%. Following the occurrence of a measles case in a child after a visit outside, twenty-six children developed measles later. The secondary attack rate of measles is: (UPSC CMS 2013) a)16.6% b)26% c)65% d)66.6% Most universally accepted indicator of health status of whole population and their socio-economic status among the following is- (AIIMS 2001) a)MMR b)IMR c)Life expectancy d)Disease notification rates Which of the following is the most logical sequence? (AIIMS 2006) a)Impairment- disease – disability- handicap b)Disease- impairment – disability – handicap c)Disease – impairment – handicap- disability d)Disease- handicap – impairment – disability Regarding Human poverty Index-1 (for developing countries), the incorrect indicator is- a) Probability at birth of not surviving to age 60 years b) Adult illiteracy rate c) Proportion of population not using an improved source of water d) Proportion of children underweight for age Part I of the death certificate deals with a)Immediate cause, and the direct underlying cause which started the whole trend of events leading to death b)Any significant associated disease that contributed to the death but did not directly lead to it c)Approximate time interval between onset and cause of death d)Mode of death EPIDEMIOLOGY EPIDEMIOLOGY Epidemiology is the study of the distribution and determinants of health-related states or events (including disease), and the application of this study to the control of diseases and other health problems. Types of epidemiological studies

DESCRIPTIVE EPIDEMIOLOGY

• Usually the first phase of any epidemiological study • Observing the distribution of health-related characteristics in populations and identifying the time, place and person characteristics with which the disease seems to be associated

Time distribution

• Short-term fluctuations • Point source epidemic • Common source/ multiple/continuous exposure epidemics • Propagated epidemic • Periodic fluctuations • Long term or secular trend

Endemic Continued transmission of a disease, in a defined population or area, at a relatively low level (without any importation from an outside area or population). Based upon the proportion of population affected, endemic situations in diseases like malaria are graded as hypoendemic, mesoendemic, hyperendemic and holoendemic. Sporadic Few, scattered cases of infection, which do not have any relation temporally / spatially. Epidemic It is the unusual occurrence in a community/ region of disease / health-related event/ health -related behavior clearly in excess of expected occurrence. Pandemic An epidemic occurring worldwide, or over a very wide area, crossing international boundaries and usually affecting a large number of people Methods of measurement in descriptive studies • Cross sectional studies • Longitudinal studies

Cross sectional studies

• Prevalence study • Single examination of population at one point of time • More useful for chronic diseases • Gives information only about distribution and not etiology

Longitudinal studies

• Observations are repeated in the same population over a prolonged period of time • Useful to study natural history of a disease • Helps in identifying risk factors • Incidence rate can be obtained • Temporal association can be deduced

Ecological studies

• In ecological studies, the unit of observation is an aggregate, a town or a whole country etc. • Population as unit of study • Involves the investigation of the characteristics of a disease in a whole population • This is in contrast to studies that investigate the characteristics of a disease in an individual

Design of case control study

First select Then Cases Controls measure past (Have (Do not have exposure disease) disease) Were a b Odds’ s ratio = a d exposed b c Were not c d exposed Total a + c b + d Proportions a /a + c b/b + d exposed Design - Cohort study

First Follow-up to see whether disease select develops Disease No Total Incidenc disease e rate

Exposed a b a +b a / a+ b Not c d c + d c / c + d exposed • Absolute risk: Incidence rate is a measurement of absolute risk

• Relative risk: Incidence of disease among exposed Incidence of disease among non-exposed

• Attributable risk: Incidence of disease among exposed - Incidence of disease among non-exposed Incidence of disease among exposed

• Retrospective Cohort Study • Nested Case Control Study

Advantages of nested case control study over a case control study • Can utilize the exposure and confounder data originally collected before the onset of the disease, thus reducing potential recall bias and temporal ambiguity, • Include cases and controls drawn from the same cohort, decreasing the likelihood of selection bias and need for long follow up

Blinding • Single: Subject/Patient blind • Double: Investigator + Subject/Patient blinded • Triple: Investigator + Subject/Patient + Analyst blinded

Major criteria Minor Criteria Temporal association Strength of association Cause should precede the Measured by odd’s ratio, Relative US Surgeon effect risk and correlation coefficient. The General’s stronger is the association, the more likely it is to be causative Criteria for Biological plausibility/ Dose-response relationship Causation Coherence Does the risk increase with increase Does the association fit with in exposure? other biological knowledge? Consideration of alternate Cessation of exposure hypothesis Does stopping the cause, decrease Have other possible or annul the risk? alternative causes been considered? Replication of findings / Specificity of association consistency Causality is enhanced if an exposure Is the same association is associated with a specific disease, found in many studies? and not with a whole variety of diseases Residents of three villages with three different types of water supply were asked to participate in a study to identify cholera carriers. Because several cholera deaths had occurred in the recent past, virtually everyone present at the time submitted to examination. The proportions of residents in each village who were carriers of cholera were computed and compared. This study is- (AIIMS 2003) a)Cross-sectional study b)Case-control study c)Concurrent cohort study d)Non-concurrent study

The most difficult criterion to establish causal association in etiology of a disease is- (AIPGME 2008) a)Temporality b)Strength of association c)Specificity of association d)Biological plausibility Several studies have shown that 85% of cases of lung cancer are due to cigarette smoking. It is a measure of - (AIPGME 2007, AIIMS 2005) a)Incidence rate b)Relative risk c)Attributable risk d)Absolute risk Of the different epidemiological study designs available to test the association between risk factor and disease, the best design is of- (AIIMS 2005) a)Case-control study b)Ecological study c)Cohort study d)Cross-sectional study In a study begun in 1965, a group of 3000 adults in Baltimore were asked about alcohol consumption. The occurrence of cancer was studied in the group between 1981 and 1995. This is an example of- (AIPGME 2004) a)Cross sectional study b)Concurrent cohort study c)Retrospective cohort study d)Clinical trial The systematic distortion of retrospective studies that can be eliminated by a prospective design is- (AIIMS 2004) a)Confounding factor b)Effect modification c)Recall bias d)Measurement bias Incidence of a disease can be obtained through (AIIMS 2010, 2011) a)Cross sectional study b)Case control study c)Prospective study d)Retrospective study In a study in UK, an association was found between sale of anti- arrhythmic drug and an increase in deaths due to asthma. This is an example of: (AIIMS 2006, 2008, 2011) a)Ecological study b)Cohort study c)Case reference study d)Experimental study Strength of association is given by (AIIMS 2009) a)p-value b)Coefficient of regression c)Alpha value d)Odds ratio Matching is done for removal of (AIIMS 2015) a)Bias b)Known confounding factors c)Unknown confounding factors d)Known and unknown confounding factors True about a confounding factor is (AIIMS 2009) a)It is found equally between the study and the control groups b)It is itself a risk factor for the disease c)Confounding can be eliminated by selecting a small group for study d)It is associated either with exposure or the disease True about attributable risk is all, except a) It is based on the difference in incidence rates of disease between exposed and non exposed group b) Also known as risk difference c) It indicates the strength of association between the suspected cause and effect d) It suggests the amount of disease that might be eliminated if the factor under study could be controlled or eliminated Infectious diseases Epidemiology • Source of infection- the person, animal, object or substance from which an infectious agent is disseminated to the host is called source of infection. • Reservoir- it is any person, animal, plant, arthropod or substance (or a combination of these) in which an infectious agent lives and multiplies , on which it depends primarily for its survival and where it reproduces itself in such a manner that it can be transmitted to a susceptible host. • Carrier- An infected person or animal that harbors a specific infectious agent in the absence of discernible clinical disease and serves as a potential source of infection for others • Vector- it is any living carrier that transports an infectious agent to the susceptible host. Prodromal period The time interval between the invasion of an infectious agent and the appearance of first sign of the disease. Incubation period The time interval between the invasion of an infectious agent and the appearance of first symptoms of the disease Latent period It is the time interval between the disease initiation and (Non-infectious disease detection diseases) Latent period- (in It is the time interval between the entry of the infectious infectious agent in the body and the start of the shedding of the diseases) organism Generation time It is the time interval between the receipt of infection by a host and the maximal infectivity of that host Communicable It is the time period during which an infectious agent may period/ infectious be transferred from an infected person to another living period being. • Isolation – It is the separation of infected persons or animals for the period of communicability in such places and such conditions so as to prevent or limit direct or indirect transmission of infection to those who are susceptible or those who may spread the agent to others. • Quarantine- it is the limitation of freedom of movement of such well persons/ animals/ objects exposed to communicable disease for a period up to the longest incubation period in such a manner so as to prevent effective contact with those not so exposed.

Iceberg phenomenon • Visible part- symptomatic, detected • Invisible part- latent, unapparent, pre-symptomatic, undiagnosed and carriers • E.g. hypertension, diabetes, anemia, malnutrition, mental diseases.

This phenomenon is not shown by- • Rabies • Tetanus • Measles • Pertussis

Importance of incubation period • Helps in tracing the source of infection; e.g. food poisoning • Helps in determining the period of surveillance, e.g. in quarantine • Helps in determining the period during which antisera must be administered for preventing clinical disease. • Identification of point source epidemics as against propagated epidemics • Helps in estimating the prognosis of disease, e.g. in tetanus/ rabies, where shorter incubation period reflects poorer prognosis.

Modes of transmission of diseases by arthropods

• Direct contact- two hosts are in direct contact with each other; vector itself gets transferred from one host to another. E.g. Pediculosis, scabies, • Mechanical transmission- the organism is transmitted on the outside or inside the bodies of arthropods with no development / propagation. E.g. diseases transmitted by houseflies. • Biological transmission- The organism undergoes some biological change.

Biological transmission

The organism undergoes some biological change. it is of following types. • Cyclodevelopmental- a part of the life cycle is completed in the vector. e.g. W. bancrofti in Culex. • Cyclo-propogative- undergoes development as well as multiplication. e.g. plasmodium in mosquitoes • Propogative- simply grows and multiplies. E.g. Yersinia pestis in Rat flea and all bacterial, viral, spirochetal or Rickettsial diseases.

Endemic disease means that a disease- (AIPGME 2005) a) Occurs clearly in excess of normal expectancy b) Is constantly present in a given population c) Exhibits seasonal pattern d) Is prevalent among animals

Application of Incubation period is all except (AIIMS 2012) a)To differentiate co-primary cases from secondary cases b)To find out time for isolation c)To find out time for Quarantine d)To prevent infection to the contacts of the infected person Carriers are important in all except- (AIPGME 2002, 2007, 2011) a)Polio b)Typhoid c)Measles d)Diphtheria Serial interval is the gap between: (UPSC CMS 2013) a)Primary and secondary case b)Index and primary case c)Introduction of infection and development of maximum infectivity d)Transmission of infection from patient to another susceptible host The situation in which, causative agent is present but there is no transmission, is known as- (AIPGME 2012) a)Elimination b)Control c)Eradication d)Holoendemic The area is declared free of epidemic, when (AIIMS 2007) a)The last secondary case recovers b)No new case reported for the incubation period of disease since the last case c)No new case reported for twice the incubation period of disease since the last case d)No new case reported for six months since the last case Which of the following mode of biological transmission is seen in Dengue fever? a) Propagative b) Cyclo-developmental c) Cyclo-propagative d) None of the above All of the following statements about quarantine are true except- a)It is synonymous with isolation b)Absolute quarantine is restriction during the incubation period c)Exclusion of children from school is an example of modified quarantine d)Quarantine should not be longer than the longest incubation period Secular trend is best demonstrated by- a)Line diagram b)Bar graph c)Stem-leaf plot d)Box and whisker plot Natural history of a disease is best studied by a)Cross sectional study b)RCT c)Case control study d)Cohort study True about point source epidemic is- a)Occurs in more than 1 incubation period b)Occurs in 1 incubation period c)The exposure is continuous d)Epidemic curve falls very slowly Time interval between receipt of infection and maximal infectivity of the host is known as- a)Generation time b)Incubation period c)Serial interval d)Secondary attack rate THE END