Introduction to Epidemiology PDF

INTRODUCTION BY AHMED GHANDOUR  Definition of community medicine It is the branch of medicine that gets use of all scientific health information gathered from: 1. Epidemiology 2. Biostatistics 3. Preventive medicine and public health 4. Demography 5. Health manag...

INTRODUCTION BY AHMED GHANDOUR  Definition of community medicine It is the branch of medicine that gets use of all scientific health information gathered from: 1. Epidemiology 2. Biostatistics 3. Preventive medicine and public health 4. Demography 5. Health management 6. Environmental sanitation 7. Occupational health 8. Other related science such as behavioral and social sciences. For meeting the health needs of the community as a whole.  Preventive Medicine: It is the science of application of the different levels of prevention at the population, community and individuals. Public health Public Health defined as 'the science and art of preventing disease, prolonging life and promoting health and efficiency through organized community measures such as control of infection, sanitation, health education, health services and legislation, etc.  Social Medicine: It is defined as the study of the man as a social being in his total environment. It stands on two pillars- medicine and sociology. It is concerned with the health of groups of individuals as w II as individuals within groups.  Goals of community medicine I. Promotion of health II. Preservation of health III. Correcting of any departure from health that interfere with the wellbeing of the community.  Community Medicine Main items which is concerned by community medicine: 1.Disease or health problem: – Natural history – Distribution – Why arise – Methods of prevention – Health services and programs provided to prevent it. 2.Measuring and evaluation of health status of population 3.Raising the level of health of the population.  Health and Disease Definition: (WHO) It is a state of compete physical, mental & social wellbeing and not merely the absence of disease or infirmity.  Dimensions of health: Physical Health: The state of physical health implies the notion of "perfect functioning" of the body. It is a state in which every cell and every organ is functioning at optimum capacity and in perfect harmony with the rest of the body. Mental Health: A mentally healthy person is free from internal conflicts, He is able to get on well with others, He is well adjusted, He has good self-control and He faces problems and tries to solve them intelligently.  Dimensions of health: Social Health: It takes into account that every individual is part of a family and of wider community. The social, cultural and economic conditions in which we live have an impact on the health and disease of individuals and communities.  Levels of Health Ideal Health: It confirms the WHO definition of health. Positive Health: In which there is a reserve of health which enables the individual or the community to face the physical, mental and social problems without the appearance of any symptoms or signs of diseases. Average Health: The individual is healthy but when faces any physical, mental or social problem he become diseased.  Levels of Health In-apparent disease: A diseased person showing no signs or symptoms. But the disease can be discovered by investigations. Apparent disease: A diseased person showing symptoms & signs of the disease. Death: The end of the health spectrum.  Factors affecting health [Determinants of health] 1. The environment 2. Genetics 3. Nutrition 4. Behaviour 5. Level of immunity(herd immunity) 6. Health care system and programs  Disease It is deviation from normal health status with characteristic symptoms and signs. (May be communicable or non communicable) Communicable disease : It is characterized by: 1. Caused by a biological agent as bacteria , virus…etc 2. Transmitted from a source of infection to susceptible host through channels of transmission (one or more) Non communicable disease: It is non transmissible disease such as CHD, DM, Hypertension…. etc..  Important Definitions Infection: It is invasion of human body with a pathogenic agent. Infectious disease: It a clinically manifest disease resulting from infection N.B. Infection ≠ infectious disease. Non infectious disease: It a disease is not due to infectious agent as DM. Contagious disease: Disease transmitted from person to another by direct contact as scabies, leprosy…etc. Iatrogenic disease: It is a physician induced disease e.g., prenatal x-ray → childhood leukemia, infected blood transfusion → HBV – AIDS ….etc. Opportunistic infection: It is infection by an organism that takes the opportunity provided by a defect in the host defense mechanism e.g., AIDS. Ecology of the disease: It is the interaction between the host, agent and environment that affect this disease. Infestation: Invasion of the host by ectoparasite e.g., worm. Contamination: The presence of living infectious agents on the exterior surface of the body or on the clothes or articles of the person or on any inanimate object in the environment including water and food. Decontamination: It is removing of contaminants such as microorganisms, radioactive substances, hazardous chemical material,..etc Disinfection: A process of killing pathogenic microorganisms (doesn’t include spores). Disinfectant is a chemical agent used for the process of disinfection. Sterilization: A process that kills all viable microorganisms. i.e. absolute germ free state. Infectivity: It refers to the proportion of exposed persons who become infected. Pathogenicity: It refers to the proportion of infected persons who develop clinical disease. Virulence: It refers to the proportion of persons with clinical disease who become severely ill or die.  Epidemiology Definition: * It is the study of the distribution and determinants of health related states or events in specified populations and the application of this study to the control of the health problems. [Epi = upon Demos = people Ology = science] Distribution: related to person / place/ time = Descriptive epidemiology. Determinants: include both causes and factors that influence the risk of diseases = Analytic epidemiology.  Uses of epidemiology 1. Searching for causes of disease 2. Community assessment 3. Evaluating community health programs and intervention 4. Identification of syndromes (Lumping and splitting) 5. Completing the clinical picture 6. Improving the diagnosis and treatment and prognosis of diseases. 7. Investigating the mode of transmission of new disease. 8. Clinical decision analysis: 9. By studying time trends → predict some future development and devise means of control. Epidemiological triad (triangle) * Theory of disease causation: 1. Single disease theory: [old theory] any disease has one single cause e.g., typhoid bacilli cause typhoid fever. 2. Multiple causation theory: health and disease are affected by 3 groups of factors → agent - host - environment Epidemiological triad or triangle Definition: It is the 3 groups of factors operating in the prepathogenesis period of natural history of disease 1. Agent Agent 2. Host 3. Environment Host Environment  I- Agent factors: Definition of causative agent of a disease: is a factor that influences the occurrence of a disease → ↑ factor → ↑ disease occurrence ↓ factor → ↓ disease occurrence 1. Biological agents: bacteria – virus- parasite … etc. 2. Chemical agents: organic or inorganic chemicals 3. Physical agents: heat – cold – light – noise … etc. 4. Psychological agents: worries –internal conflicts..etc. 5. Traumatic agents: accidents - floods … etc.  II- Host factors: Host factors → intrinsic factors that influence an individual's exposure, susceptibility or response to causative agent. Age, sex, race, socioeconomic status and behaviors (e.g., smoking, eating habits…etc.) genetic composition – nutritional status – immunological status – anatomic structure – presence of disease or medications and psychological makeup  Environmental factors: A. Physical factors: 1. Geologic factors: as type of soil (which determine type of agriculture), food and water supply. 2. Geographical factors: as location of the city. 3. Climatic factors: as temperature – humidity – winds. B- Biological factors: as insects. C. Sociocultural factors: as population density – Sanitation - Educational status - Economic level - Medical health facilities - Means of transportation [providing medical care & rapid spread of infection from one locality to another]  Natural history of disease Definition: It refers to the progress of a disease in an individual over time, in the absence of intervention. It begins with exposure to or accumulation of factors capable of causing disease (e.g., microorganisms for infectious disease or cancer initiators as asbestos or tobacco → lung cancer or cancer promoters as estrogens → endometrial cancer) without medical intervention, the process ends with → recovery, disability or death.  Usual time of Pathologic changes diagnosis Stage Stage of symptoms symptoms Exposure Stage of sub clinical Stage of clinical disease Stage of recovery, Stage of susceptibility disease disability or death (stage of pre symptomatic) [Pre pathogenic period] [Pathogenic period]  The usual course of a disease may be halted at any point in the progression by → Preventive measure → therapeutic measures → host factors → other influences. Stage of subclinical disease called: → incubation period [infectious diseases] → latency period [chronic diseases] The subclincial period varies form seconds as in hypersensitivity to decades as in AIDS & hepatitis. In subclincial period → no symptoms but there are pathologic changes → may be detected by screening tests (laboratory, radiographic … etc.)]  Pattern of occurrence of infectious diseases * 1. Endemic pattern: – It is persistent occurrence of disease in a certain community (low or moderate level)? – Another definition: it is usual prevalence of a given disease within a given geographic area. 2. Sporadic: – Scattered occurrence of cases of disease in very small number and over wide area. – Under optimal conditions may start an outbreak or even epidemic. 3. Epidemic: Sudden occurrence of large number of cases in excess of normal expectancy in a community in a short time. Endemo –epidemic: under optimal conditions, the endemic disease may flare up and cases clearly exceed seasonal endemic pattern. Exotic- epidemic: these are imported communicable disease 4. Pandemic: – It is an epidemic involving more than one country e.g., AIDS, cholera. 5. Outbreak: – It an epidemic on a small scale, among a confined group in a closed community as prison, school. Chain (cycle) of infection * Reservoir of infection Susceptible host Portal of entry Portal of exit Agent Mode of transmission  Ι - Reservoir of infection Definition: it is a man, animal, soil or organic matter in which infectious agent can live and multiply. So, reservoir of infection may be: Human Animal Inanimate Man and animal →most important source of infection.  Human reservoirs A - Case 1. Frank case [Mild, moderate, severe] 2. Abortive case (missed case) B - Carrier [Sub-clinical infection] [in-apparent infection] NB: severe cases are not necessarily more infectious than mild or sub-clinical cases.  Carrier Definition: is a person who harbors the infective agents, acting as a source of infection without showing any symptoms or signs of the disease. Classification: 1. According to spectrum of disease 2. According to the duration. 3. According to habitat of the organism.  According to spectrum of disease A. Incubatory carrier: discharging the organism during the IP e.g., measles, mumps. B. Healthy carrier: discharging the organism during sub-clinical period e.g., menigeococcla meningitis. C. Contact carrier: as healthy carrier but gives a history of being in contact with infected person e.g. diphtheria. D. Convalescent carrier: discharging the organism during convalescence period e.g., typhoid fever.  According to the duration A. Transient carrier: few days to few weeks e.g., cholera B. Temporary carrier: few weeks to some months e.g., hepatitis. C. Chronic carrier: ↑ 1 year e.g., AIDS. D. Permanent carrier: throughout life e.g., typhoid (rare case).  According to habitat of the organism A. Nasal carrier: as diphtheria B. Throat carrier: as cerebrospinal meningitis C. Intestinal carrier: as typhoid, cholera. D. Urinary carrier: as typhoid.  Importance of carrier as source of infection Because of: 1. They move freely in the community 2. They are greater number than cases 3. They are difficult to diagnose 4. They persist for long time Dangerous group of carriers: [Food handlers, Servants, Baby sitters, Housekeepers, School and hospital personnel, Coiffeurs and ticket conductors] B. Animal reservoirs: Animals may be cases or carriers for many diseases. e.g., rabies & bovine TB [Zoonosis: disease that are transmitted from animal to human] C. Inanimate reservoirs: Including soil – plant and organic matter e.g. tetanus – anthrax.  II. Portal of exit 1. Respiratory tract → e.g. diphtheria 2. Intestinal tract → e.g. typhoid (feces), cholera (vomitus). 3. Urinary tract → e.g. typhoid 4. Trans-plancental →e.g. syphilis – AIDS. 5. Mechanical → e.g. insect bite – syringes blood. 6. Open lesion → e.g. skin infection – STDs  III. Mode of transmission A - Direct transmission: – Direct contact – Droplets – Transplancental B - Indirect transmission: – Vector transmission (vector – borne infection) – Vehicles transmission (vehicle borne infection) – Air borne – Soil borne  Direct transmission It means close association between the infected man or animal and the new host without a 3rd object. 1. Direct contact: By touch, kissing, sexual intercourse with infected person Also, by contact with animal e.g., biting (rabies) 2. Droplet transmission: Droplets are particles of moisture including the infecting organisms expelled from respiratory tract by coughing, sneezing, laughing or even talking (limited distance 1-2 meter) e.g., measles , diphtheria, influenza. NB: droplets → may fall in ground → contaminating soil, food or article (indirect). 3. Transplacental transmission: from Mother through placenta to fetus, e.g., syphilis – AIDS  Indirect transmission A. Vector transmission (vector – born infection) Most vectors → arthropods as mosquitoes, fleas, ticks. Their role is either mechanical or biological B. Vehicles transmission (vehicle borne infection) Water Milk & its products: Food Fomites C. Air borne Droplet nuclei Dust nuclei D. Soil borne  Vector transmission 1. Mechanical transmission: A - Direct : e.g., house flies become contaminated from discharges of infected eye then → transmit it to a healthy eye as in purulent conjunctivitis B - Indirect : e.g., house flies carry pathogenic organisms (on feet – mouth part or ingested and pass in insect feces or vomitus) → then will contaminate food as in typhoid & cholera. 2. Biological transmission: The agent has to pass through some biological activity inside the vector which requires a certain period of time (extrinsic IP). After this period, the insect is then able to transmit infection to the new host. The biological transmission can be: 1. Preparative biological transmission: simple multiplication of the causative agent in the vector e.g., pasturella pestis (flea) 2. Cyclopropagative: organisms multiply and undergo changes within the vector e.g., malaria. 3. Cyclodevelopmental: organism have a cycle of developmental changes inside the vector e.g., filaria in mosquito  Vehicle transmission 1. Water: it can be contaminated from excreta as feces and urine → e.g., cholera – typhoid – dysentery (bacillary – amoebic) 2. Milk & its products: It can be contaminated by Man or Animal: Animal → pathogens excreted in milk of infected animal e.g., bovine TB. → pathogens coming from infected udder e.g. streptococcal infection. → milk contaminated with excreta of animal e.g., anthrax. Man → droplets e.g. diphtheria, scarlet fever → discharges from skin lesions or nasal discharges e.g., staph food poisoning. → using contaminated water in washing utensils used for milk or for milk adulteration. 3. Food: May be due to: a. The animal used as food may be already infected e.g., cattle with salmonellosis or pigs with trichniasis. b. Contamination of food or drink from: insects – food handlers - soiled utensils – tables – knives… etc. c. Improper (defective) storage of food d. Contaminated food items (vegetable – fruits … etc.) → eaten raw without proper washing. 4. Fomites: Fomites → are different objects (e.g., clothes, toys, utensils, linens… etc) which being contaminated from the reservoirs.  Air borne transmission A - Droplet nuclei: It is the small particles result from evaporation of the fluids from the droplets of infected person. They contain pathogens and remains suspended in air for a long time in a sort of unseen smoke, which is dispersed here and there by the air current → inhaled by susceptible host → infection. e.g. spread of measles may occur from room to room or from word to word in hospital. B - Dust nuclei: It is the large particles → fall on the ground → mix with dust → become part of dust. The organisms resist drying for a long time as TB – haemolytic streptococci. Dust may be contaminated by → droplet – spitting on ground – excreta. Contaminated dust may: → Dispersed in air → e.g., TB, respiratory infection. → soils articles (utensils – bedding – clothes …. etc.) → fall on skin → skin infection or tetanus. → fall on syringes, instruments or dressings → wound infection.  Soil-borne transmission: as in ancylostomiasis - ascariasis.  IV – Portal of entry Respiratory tract → by inhalation GIT → by ingestion Skin and MM→ by direct invasion – vector Blood → by inoculation  V – The susceptible host It is a person or animal (including birds and arthropod) who get infected by infectious agent under natural conditions. Factors affecting the susceptibility: – Genetic factors – General factors: Natural resistance (skin- m.m. – cilia or resp. tract. – cough reflex…etc.) Malnutrition, alcoholism, presence of diseases or therapy which impairs immune system →↑ susceptibility. – Immunity – Behavior  Immunity Passive : It is the type of immunity in which ready made antibodies are gained. It is 2 types: 1. Natural 2. Artificial Active : It is the type of immunity in which the person makes or develops his own antibodies. It is 2 types: 1. Natural 2. Artificial  Passive immunity 1. Natural passive immunity (infant immunity): It is resistance of infant through: a. Maternal antibodies b. Maternal milk (esp. colostrums) → 95% of its protein is immunoglobulins. These antibodies are at their highest level → at birth then → gradual decline till become insignificant → at 6 months. Natural passive immunity in the infant could be induced artificially by immunizing the mother during pregnancy e.g., immunization of tetanus toxoid to protect the newly born infant against tetanus neonatorum. 2. Artificial passive immunity: (passive immunization) It is the immunity induced by injecting immune serum or gammaglobulin. It is of short period → about 3 weeks e.g. a. Sera of artificially immunized animals as antitetanic & antidiphtheritic sera → used in prophylaxis or treatment. b. Gamma globulin: it is a plasma protein fraction that carries most of antibodies present in the body as measles and hepatitis A. [Gamma globulin → used in prophylaxis only]  Active immunity 1. Natural actively acquired immunity: (Post-infection immunity) – It may by solid or for a long time as in case of mump – measles. – It may be moderate duration (years) as in case of meningitis – It may be short period as in case of common cold 2. Artificial actively acquired immunity: (vaccination) It is produced artificially by active immunization → using an immunizing agent which is a specific antigens when introduced in the body → provoke antibodies formation. The ideal immunizing agent: 1. Stable antigenically 2. Reasonable cost 3. Give potent immunity 4. Keeping quality is good 5. Minimal side effects 6. Easy in administration  Types of immunizing agents (vaccines) A. Live attenuated vaccines: 1. Attenuated vaccine: micro-organisms lose their pathogenicity but retain their antigenicity as MMR vaccine 2. Variant forms of living organisms vaccine: In these vaccines a milder species of the organisms closely related antigenically to the human disease agents are used as BCG vaccine using bovine tubercle bacilli - small pox vaccine using cow pox virus. [Attenuation can be done by repeated sub-cultures or cultivation under un-favorable conditions ] B. Non-living vaccines: 1. Killed or inactivated vaccines: Killed bacterial organism using heat or chemicals [as ether and Formalin]. As TAB vaccine - whooping cough vaccine. Inactivated virus as Salk vaccine. 2. Toxoid vaccines : (products of organisms) Toxoid is the toxins after loosing their toxicity but retaining their antigenicity as diphtheria toxoid – tetanus toxoid. 3. Part of organisms: As the subunit of hepatitis B surface antigen (HBsAg) prepared from plasma of HBsAg positive carriers or by Genetic engineering. As part of polysaccharide capsule of Nisseria meningitides used as vaccine against meningeococcal meningitis.  Herd immunity * Definition: -it is a state of immunity within the community. Herd immunity is the factor that decides the epidemiological pattern of any infectious disease among the community. The incidence of a disease raises at times when the number of susceptible in the population is highest and the herd immunity if lowest. Herd immunity is affected by: – The extent of coverage of mass vaccination – The degree of resistance afforded by vaccine – Past experience with different infection – Duration and degree of infectivity of the organisms – Environmental sanitation and overcrowding sanitation.  Incubation period * Definition: It is the interval between the entry of infective agent into a susceptible host and the appearance of symptoms and signs of the disease. It depends on: 1. Type of infective agent → organism – toxin. 2. Dosage and virulence of infective agent. 3. Host resistance. Each disease has its own IP. IP varies from few hours to few years. Types of IP: 1. Intrinsic IP : In man [as definition] 2. Extrinsic IP : In vector it is the Period between the time the vector gets infected and time the vector become infected [It is required for development or multiplication of pathogenic agent]. Importance of IP: 1. To know the probable date of exposure to source of infection → tracing the source of infection 2. To apply preventive measures in certain disease as in measles: if measles vaccine given to the contact in 1st 3 days after exposure → it will prevent the disease. 3. To evaluate the control measures: if good control measures → no 2ry cases, if not efficient control measures → 2ry cases (2ry cases = cases that appear for a period longer than IP). 4. To decide the period required for isolation – surveillance or segregation of contacts. 5. To differentiate between pattern of epidemic curve 6. Quarantinable measures of international travelers. e.g. for travelers coming from endemic area of cholera without having valid vaccination certificate → they are quarantined for 5 days (IP of cholera).  Period of communicability (infectivity) * Definition: It is the time during which the causative agent may be transferred directly or indirectly from infected individual to another or from an infected animal to man.  Epidemic curve * Definition: It is a line graph (frequency polygon) → showing the number of cases of an epidemic every defined period of time. Phases: 1. Phase of evolution: represented by → ascending limb :steep (abrupt) rise, gradual rise 2. Phase of decline: represented by → descending limb: steep (abrupt) rise, gradual rise 3. Peak : acute – broad – flat (plateau)  Phase of evolution: a. Steep or abrupt rise: b. Gradual rise Suggesting Suggesting Short impulse → short period Continuous impulse → long of contamination period of contamination Short IP Long IP Rapid rate of dissemination of Slow rate of dissemination of infection infection  Phase of decline: a. Steep or abrupt decline: b. Gradual decline Suggesting Suggesting Short impulse Continuous impulse Short IP Long IP Effective control measures Deficient control measures Rapid exhaustion of susceptible Occurrence of 2ry cases in the community Peak of the epidemic curve: a. Acute peak → steep ascending & descending limbs b. Broad peak → gradual ascending & descending limbs c. Flat (plateau) peak → rare: suggesting; 1. Sustained source of infection 2. sustained susceptible in the community 3. Ineffective control measures. 4. Continuous favorable environmental background for the spread of infection.  Types of epidemic curve * Explosive type: common source Epidemic common vehicle Epidemic e.g.: water or food contamination Progressive type: contact Epidemic e.g. : Droplet epidemic Prevention of communicable disease These are actions taken prior to the disease onset which control the causation and the risk factors → thus limit the incidence or prevent the possibility of occurrence of a disease. Measures of prevention: 1. Health education 2. Environmental sanitation – safe water supply – clear air – adequate sewage and refuse – good housing – anti flies measure 3. Adequate nutrition 4. Specific protection – immunization – chemoprophylaxis – protection from carcinogens and allergens – protection against accidents – protection against occupation hazards Control of communicable disease 1. Control of cases 2. Control of contacts 3. Control of environment 4. International measures 1. Control of cases: a. Case finding: Clinical diagnosis and laboratory confirmation if necessary. The earlier → the better for case, contacts and community. b. Notification: Cases (definite or suspected)→ must be notified to an appropriate authority → MOHP → WHO (in specific diseases) c. Isolation: The infectious case must be isolated → at home, hospital or special place → according to nature of disease and home condition. Period of isolation varies according to period of communicability d. Disinfection: It is the process of destroying pathogenic organisms outside the body. Concurrent disinfection: Disinfection is carried out during the course of disease → for – excreta and discharges – soiled articles and fomites – any object or material used in nursing Terminal disinfection: Disinfection for the last time → after transferring the case, cure or death → for the place and contaminated belonging of the patient.  e. Treatment: specific therapy as chemotherapy or antitoxins nursing and proper feeding symptomatic treatment prevention and control of squeal and complications f. Release : The case can leave isolation and return to school or work after: Clinical recovery Satisfactory general condition Becoming bacteriologically free → in disease with convalescent carriers. 2. Control of contacts a. Enlistment: a special contacts list is filled for names and personal data b. Search for carriers: using screening tests c. Surveillance, segregation or isolation: according to the disease. 4. Specific protection: by – Immunization → active as measles, passive as diphtheria. – Chemoprophylaxis e.g., tetracycline in cholera. a. Surveillance: It is the supervision of contacts to permit recognition of infection or illness without restricting their movements. The period of observation is equal to longest IP of the disease under observation.. b. Segregation: As in measles – diphtheria – enterica. It is an exclusion from school or work ( not isolation) → until prove not to be case or carrier. (for IP or after becoming bacteriological free in diseases with convalescent carrier as diphtheria). c. Isolation: In serious diseases only. It means separation of contacts in a specific place (quarantine) → to prevent direct or indirect contact between them and unexposed individuals. Period of isolation is for the longest IP counted from date of last exposure. It occurs only in case of contacts of → pneumonic plague – pneumonic anthrax – cholera in non-endemic area. 3. Control of environment: According to the disease as: → food sanitation → super-chlorination of water → sanitary sewage and refuse disposal → adequate ventilation → insect control → health education to at risk group or to population. → specific measures: → mass active immunization or chemoprophylaxis (if available) to at-risk group. 4. International prevention : It is some international regulations which followed by many countries → to prevent transmission of particular infectious diseases (quarantine disease) from on country to other. These measures: → international travelers → imported animals → imported goods  Investigation of outbreak or epidemic * Steps: prepare for field work ensure the existence of epidemic or outbreak confirm the diagnosis define and count the cases performing descriptive epidemiology determine the population at risk hypotheses formulation evaluation hypotheses implementing control and preventive measures communicating the findings NB: these steps are in conceptual order, in practice → several steps may done at the same time or different order may be followed according to circumstances of the outbreak. Prepare for field work: Preparation can be grouped into 3 categories: a. Investigation: 1st, for field investigation, must have appropriate scientific knowledge, supplies and equipments to carry out the investigation. Before leaving for a filed investigation, consultations with laboratory staff should be held to prepare the proper laboratory material and assure proper sample collection, storage and transportation techniques. b. Administration: Administrative procedures as traveling… etc. c. Consultation: Everyone must know the expected role in the field. Ensure the existence of an epidemic or outbreak: Requires comparison with present incidence and previous incidence → to determine the existence of the epidemic or outbreak. Difference between epidemic and outbreak → see before. Confirm the diagnosis: Reviewing clinical findings and laboratory results is essential. Visiting the several patients with the disease → to gather critical information from patients such as: 1. what were their exposures before becoming ill? 2. What do they think caused their illness? 3. Do they know anyone else with the disease? 4. Do they have anything in common with others who have the disease? 5. Conversations with patients → helpful in generating hypotheses about disease etiology and spread. Define and count the cases: A. Establishing a case definition: Case definition can classified as: 1. Confirmed → must have laboratory verification 2. Probable → has typical clinical features of the disease without laboratory confirmation. 3. Possible → few typical clinical features. B. Identifying and counting cases: For every case, the following information should be collected: – Identifying information → name – address – telephone no – Demographic information → age – sex – occupation. – Clinical information → date of onset – hospitalization, disease pattern … – Risk factor information – Reporter information → the person who provided the case report. Performing descriptive epidemiology: time – person – place → see descriptive study. Determine the population at risk of having the health problem: Hypotheses formulation: We can generate hypotheses in variety of ways: knowledge about the disease itself what is the agent – reservoirs – vehicle? How it is transmitted? What are the known risk factors? Talking to a few of the cases: For possible exposures – conditions related to disease occurrence. Descriptive characteristics of the disease Evaluating hypotheses: We can evaluate hypotheses in one of two ways: 1. comparing the hypotheses with the established facts 2. using analytic epidemiology → to quantify relationships and explore the role of chance. Implementing control and preventive measures: Communicating the findings: usually takes 2 forms: 1. oral briefing for local authorities 2. written report: Eradication of infectious disease * It is getting rid of the causative organisms and consequently disease → in a certain area, country or world ( no reported case nor reservoirs of infection). Examples: 1. Small pox (variola) 1978 2. Rabies : in some developed countries through - vaccination of animals - quarantine of dogs and cats coming from other countries. 3. Bovine TB: in some countries through: – tuberculin testing of cattle – slaughtering of infected cattle – proper ttt of cases 4. Brucellosis: in some countries through as in bovin TB. Elimination of infectious disease * It means that endemic disease is so controlled to reach the level of "nor reported cases" while the causative agent is not necessarily eliminated e.g., Polio in Egypt →1st eliminated → then eradicated.  Surveillance * Definition: Public health surveillance → is the ongoing systematic collection, analysis, interpretation and dissemination of health data to take a public health action. Public health action ↓ Surveillance priority setting ↓ planning , implementation & collection evaluating disease analysis investigation interpretation control dissemination prevention Purposes and uses of surveillance: Monitoring health events: – detecting sudden changes in disease occurrence and distribution e.g., malaria, bilharizia surveillance. – To follow secular (long –term) trends and patterns of disease e.g., AIDS at first → homosexual then injecting drug users and their sex partners. – To monitor (identify) changes in agents and host factors e.g., changes of antigenic pattern of agents – changes of behavior of host as smoking. – Detecting changes in health care practice e.g., precautions of dentists - ↑ number of CS in some hospital.  Purposes and uses of surveillance: Link to public health action: – Investigation and control – Planning – Evaluating prevention and control measures – Generating hypotheses and stimulating public health research e.g., toxic shock syndrome and menstruating woman → 1980. Other uses of surveillance – Testing hypotheses – Archive of disease activity  Type of surveillance 1. Passive surveillance: It refers to data generated without request, intervention or contact with health authorities carrying to surveillance. These data → provide basic information necessary for studying infectious diseases in specific areas. 2. Active surveillance: It refers to collection of data (usually on a specific disease) for a relatively period of time. This type may be undertaken when a new disease is discovered –new mode of transmission is being investigated – a high risk season or year is recognized – a disease appears in a new geographic area.  Type of surveillance 3. Sentinel surveillance: It is the surveillance of a specified health event in only sample of population at risk using a sample of possible reporting sites. The sample should be representative of the total population at risk e.g., HIV in many developing countries → not feasible for health authorities to sue national population based surveillance → sentinel surveillance → health officials → define homogenous population subgroups and regions to be sampled → then identify institutions → sero – surveys → at least annually to provide statistically valid estimates of HIV prevalence.  Notifiable disease in Egypt * I. Immediate notification: II. Notification within 1 week (weekly notification): III. Notification within 1 months (monthly notification):  Immediate notification – Bacterial meningitis – Acute flaccid paralysis – HIV/AIDS – Diphtheria – Malaria – Plague – Tetanus (neonatal tetanus) – Food born disease – Unusual health event: Rift valley fever Viral hemorrhagic fever Botulism Cholera Other  Notification within 1 week (weekly notification) Typhoid fever Brucellosis TB Measles Pertussis Bloody diarrhea  Notification within 1 months (monthly notification) Acute viral hepatitis Mumps Rubella Leprosy Schistosomiasis Fascioliasis Filariasis