Epidemiology by prof. dr. rs mehta for msn students

Dr. RS Mehta, MSND, BPKIHS 1

Epidemiology

Introduction

Contents of the course:1. Definition2. Epidemiological Studies3. Uses of Epidemiology4. Epidemiology of infectious Diseases5. Control of epidemics6. Epidemiology of NCD


Definition of Epidemiology

It is the study of distribution, determinants and frequencies of diseases


Distribution of Disease

• Diseases are distributed according to:– Place– Person– Time

• Study of distribution of diseases is essential in descriptive studies


Place Distribution(Geographical distribution)

• Geography of diseases can identify the role of the following factors in disease causation:– Genes,– Environment,– Culture,– Nutrition,– Socio-economic and– Cultural factors


Person Distribution

• In descriptive studies persons should be defined by:– Age– Ethnicity– Sex– Occupation – Marital status– Behaviour


Distribution of diseases according to age

• Age is strongly related to disease:– Certain diseases are frequent in specific age

(measles in childhood, cancer in middle age, atherosclerosis in old age)

– Bimodality: some diseases affect 2 age groups (Hodgkin's disease) – 20 and 80 years

– Some diseases are more serious and progressive in specific age groups


Distribution of diseases according to sex

• Biological differences (e.g. Hormonal disorders)

• Cultural behavior (e.g. 4:1 male to female lung cancers due to smoking, and so alcohol car accidents . .)

• Some diseases are more frequent in male: duodenal ulcer, CHD ..

• Some diseases are more severe in females (CVA)


Distribution of diseases according to ethnicity

• Some diseases are more frequent among specific racial groups:

– Essential hypertension– CHD– Cancers– Sickle cell anaemia


Distribution of diseases according to marital status

• Mortality rates is lower for married males may be due to:– Healthy persons are more likely to get married

• Married persons had healthy lifestyle • STDs are more frequent among unmarried• Ca cervix is more common among married

women


Distribution of diseases according to occupation

• Occupation may alter the habit pattern of employees e.g. (night shifts may alter sleep ..)

• Occupational hazards may affect health (biological, chemical, physical, psychosocial, mechanical)


Distribution of disease according to behaviour

• Behaviour factors (smoking, alcohol, sedentary life, overeating, drug abuse, stress ..)

• Behaviour is a strong risk factor in modern-day diseases:– CHD– Cancers– CHD– Accidents


Time distribution

1. Short-term fluctuations (epidemics)2. Periodic fluctuations (seasonal trend)3. Long term fluctuations (e.g. diabetes show a

consistent upward trend in the developed countries during the last 50 years


Determinants of Diseases

• Biological factors (Bacteria, viruses etc)

• Chemical factors (pesticides, lead etc)

• Physical factors (radiation, heat ..)

• Mechanical factors (accidents)

• Psychosocial factors (stress, alcohol etc)


Frequencies of Diseases

• Fertility Rates

• Morbidity Rates

• Mortality Rates


Fertility Rates

Crude Birth Rate (1000):Number of live births during the year

Population

General fertility Rate (1000):No of live births in an area during a year

Female 15 -49


Morbidity Rates

• Incidence (1000):Number of new cases of a specific disease

during a given periodPopulation at risk

• Prevalence (100):Number of new and old cases of a specific

disease during a given periodPopulation at risk


Mortality Rates

• Crude death rate (1000)No of deaths during a year

Population• Specific death rate• Case fatality rate (100):

Deaths due to a particular diseaseTotal no of cases due to the same diseae


Survival Rate

Survival rate (100)Total patients alive after 5 years

Total patients diagnosed or treated


Standardize Mortality Rate

SMR (100)Observed deaths

Expected deaths


Years of potential life lost (YPLL)

• Is an estimate of the average years a person would have lived if he or she had not died prematurely

• The reference age should correspond roughly to the life expectancy of the population under study


Person-years of potential life lost in the United States in 2006

• Cancer 8,628,000

• Heart disease and strokes 8,760,000

• Accidents and other injuries 5,873,000

• All other causes 13,649,000 person-years


The disability-adjusted life year (DALY)

1. It is a measure of overall disease burden2. Expressed as the number of years lost due to ill-

health, disability or early death. 3. Originally developed by Harvard University for the

World Bank in 1990, 4. The WHO adopted the method in 20005. The DALY is becoming increasingly common in the

field of public health and health impact assessment


DALYs in Millions• HIV/AIDS 46.7• Lower respiratory infections 42.2 • Diarrhoeal diseases 32.2 • Malaria 30.9 8.2 4 • Neonatal infections and others - 13.4 3.• Prematurity and low birth weight 11.3 • Tuberculosis 10.8 • Road traffic accidents • COPD 3.1 • Protein-energy malnutrition 7.1


Epidemiological studies

Main Types of epidemiological Studies:1. Descriptive Studies

2. Analytical (Comparative Studies

3. Interventional studies (experimental)


Nomination

• Case control study (retrospective) e.g. Ca lung --- smoking

• Cohort study (prospective) e.g. smoking -- Ca lung• Cross-sectional Study: a study in a known short

period of time (Picture)• Longitudinal Study: observation is repeated in the

same population over a long period of time (film)• Facility-Based Study• Community-Based study


Uses of Epidemiological Studies

• Descriptive studies: To develop hypothesizes• Analytical Studies: To test hypothesis• Experimental studies: To confirm hypotheisi


Uses of Epidemiology

1. Community diagnosis2. Control of epidemics 3. Prevention and control of diseases4. Evaluation of curative and preventive measures5. Study of natural history of diseases6. Planning for Health Services7. Implementation of H. Services


Epidemiology of Infectious disease

• Definitions• Agent• Concepts of causation• Disease Transmission• Susceptible Host• Prevention


Definitions

• Infectious disease = Clinically manifested disease resulting from an infection

• Contagious disease = diseases transmitted through contact (scabies, trachoma, leprosy)

• Communicable disease = infectious illness transmitted directly or indirectly


cont. definitions

• Endemic = constant presence of a disease in an area

• Nosocomial = hospital acquired infection• Iatrogenic = physician induced disease• Exotic = disease transported in a country


Concepts of causation

• Supernatural theory• Germ theory• Multifactorial Theory• Web causation Theory


Epidemiological Triangle


Agent

HostEnvironment

Agent of infectious disease

It is a biological agent:• Viruses (HIV ,,)• Ricketsiae (Typhus ..)• Fungi (Candida ..)• Bacteria (Streptococcus)• Protozoa (Plasmodium ..)• Metazoa (tapeworms)


Nominations`

• Infectivity: ability of infectious agent to invade and multiply in human being

• Pathogenicity: ability to induce clinical disease• Virulence: Power of killing


Susceptible Host

Host factors:1. Demographic (age, sex, ethnicity ..)2. Genetics3. Immunity4. Social and economical5. Life style


Environmental Factor

Environmental factors related to the:

1. Host

2. Agent

3. Vector


Infectious Agent

• Bacteria• Virus• Fungi• Protozoa• …………


Chain of infection

• Infectious agent• Reservoir• Portal of Exit• Means of transmission• Portal of entry• Susceptible Host


Reservoir

• People• Equipment• Water• ……………….


Portal of Exit

• Excretions

• Droplet

• Skin

• ……………


1. Droplet contact

• coughs or sneezes coughing or sneezing include (at least):– Bacterial Meningitis– Common cold– Influenza– Streptococcal throat– Tuberculosis


2. Fecal-Oral Transmission

• Direct contact is rare in this route• Indirect through water, food is common• Examples:

– Cholera

– Hepatitis A


3. Sexual Transmission

• Direct Transmission (contact during intercourse)

• Indirect from secretions (semen or fluid secreted by female) examples:– HIV– Gonorrhea– Hepatitis B


4. Oral Transmission

• direct oral contact such as Kissing

• indirect by sharing a drinking glass or a cigarette.

• Most of diseases that transmitted by oral contact are forms of herpes


5. Transmission by direct contact

• They are called contagious • Examples:

– Impetigo– Syphilis– Leprosy


6. Vertical Transmission

• From mother to child (in-utero or during childbirth),

• Examples:– HIV – Hepatitis B– Syphilis


7. Iatrogenic Transmission

Transmission due to medical procedures


8. Vector borne transmission

• A vector is an organism that transmits infection

• Examples:– Flies – Gastroenteritis– Mosquitoes: Malaria, Trypansomiasis,


Portal of Entry

• Broken skin

• Mucus membranes

• Gastrointestinal/respiratory/urinary tract


Susceptible Host

• Neonates

• Diabetes

• Immunosuppressant

• Cardiopulmonary disease


Definition of an epidemic

• Abnormal increase of incidence of a disease (≥ 2 SD) or

• Doubling of cases during a week

• Appearance of unknown disease in an area


Investigation of an epidemic1. Verification of diagnosis2. Confirmation of an epidemic3. Defining population at risk4. Search for other cases5. Data analysis6. Formulation of hypothesis7. Testing hypothesis8. Evaluation of ecological factors9. Further investigation of population at risk10. Writing report


Control of epidemic

• Treatment

• Control

• Notification


Definition

Chronic diseases which have one or more of the following characteristics:

• permanent• have residual disability• non-reversible• require special training of the patient for

rehabilitation• require a long period of supervision,

observation or care


Examples of Non-communicable Diseases

• Cardiovascular diseases• CHD• Ca• Hypertension• diabetes• Accident• Blindness• Obesity


The Problem

• 32 million people die due to non-communicable diseases every year

• Affects adults• Affects the quality of life• It is increasing, mainly in developing countries– Life expectancy is increasing– Change of life style


Impact of Non-communicable diseases on the lives of people

• Disabilities

• Family hardship


Risk factors of Non-communicable diseases

• Smoking, Alcohol• Inability to obtain preventive health services• Life style changes• Stress • Environmental risk factors: (Occupational hazards,

Pollution (air, water)


Definition of Disease Prevention

Any activity which reduces morbidity and mortality of diseases


Primordial Level(Health Promotion)

• Definition: Helping people to improve Health• Interventions of Health Promotion:– Health Education promoting healthy lifestyle– Environmental modification– Nutritional Interventions


Levels of Prevention

• Primary Level

• Secondary Level

• Tertiary Level


Primary Level of Prevention

• Actions taken before the onset of a specific disease

• Examples:– Bed nets– Vaccines– ….


Secondary Level of Prevention

Early diagnosis and adequate treatment


Tertiary Level of Prevention

• Tertiary level of Prevention (Rehabilitation)– Medical rehabilitation

– Occupational rehabilitation

– Social rehabilitation

– Psychological rehabilitation


Disease Control

• An ongoing operations aimed at reducing:– The incidence of disease– The duration of disease– Complication of the disease– The financial burden to the community

• It concentrates on primary and secondary prevention


Thank You


Epidemiology by prof. dr. rs mehta for msn students

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