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OUTBREAK INVESTIGATION PowerPoint Presentation

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Description : This medical presentation has definition of Epidemic, Pandemic, Sporadic, Cluster, Endemic, Outbreak, and Types of outbreaks. The presentation also provides objectives of outbreak investigation and why outbreaks need to be investigated. Detail steps for investigation and control of outbreak (case definition and categories of cases found in outbreak investigation) and line listing method for cases and uses of line listing, and prevention and control of an outbreak.

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Published on : Mar 24, 2021 | Views : 2355 | Downloads : 6

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OUTBREAK INVESTIGATION
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Learning Outcomes At the end of this lecture students should be able to understand the followings: 1. Definition of Epidemic , Pandemic , Sporadic , Cluster, Endemic, Outbreak and Types of outbreaks. 2. Objectives of outbreak investigation & why outbreaks need to be investigated? 3. Detail steps for investigation and control of outbreak - Case definition and categories of cases found in outbreak investigation - Line listing method for cases and uses of line listing - Prevention and control of outbreak 4. Notifiable diseases and diseases under national surveillance in Malaysia
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Objectives of outbreak investigations To control continuing outbreaks To prevent future outbreaks To provide statutorily mandated services To strengthen surveillance at local level To advance knowledge about a disease To provide training opportunities
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Definition of Outbreak An outbreak or an epidemic exists when there are more cases of a particular disease than expected in a given area, or among a specific group of people, over a particular period of time. (Centers for Disease Control (CDC) and Prevention) An epidemic or a disease outbreak is the occurrence of the disease at an unusual (unexpected) frequency. (Malaysia Ministry of Health) (or)
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Differences between an Outbreak, Epidemic & Pandemic An “outbreak” and an “epidemic” essentially mean the same thing to an epidemiologist But the term “epidemic” has a more serious connotation than “outbreak” and is used less frequently to avoid the perception of a crisis situation A “pandemic” refers to a disease epidemic that is widespread and often global.
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Endemic: Constant presence of an infectious agents / disease at a low level in a delineated territory and population Epidemic/Outbreak: occurrence of specific disease at a frequency that is clearly in excess of normal expectations for a given population, time and place Pandemic: simultaneous occurrence or speedy propagation of epidemic over the wide geographic areas involving a large section of community and often global
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HOW OUTBREAKS ARE RECOGNIZED Outbreaks of disease come to the attention of public health officials in various ways: Clinical/Laboratory (astute clinician, infection control nurse, or clinical laboratory worker) Routine surveillance (analysis from Public Health Department) General public (from patient or someone close to the patient) Media (local newspaper or television news)
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Determinants of Disease Outbreaks Amount of disease in a population depends on: no. of people in population that are susceptible (at risk) no. of people immune (not at risk) If all immune  no epidemic
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Why Outbreak occurs? When susceptible person travel to an endemic area. E.g. Travel to area where Malaria is endemic. When a new infectious disease is introduce by human or animals travelling from endemic area into a susceptible human population in whom the disease is not endemic. E.g. Ebola ,travel from Africa to somewhere else When food, water or vehicles is contaminated by agent not normally present. E.g. Anthrax spore in mail as a terrorist act.
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When a preexisting infection occurs in an area of low endemic and reaches susceptible persons as a result of new or unusual social, behavioral, sexual or cultural practices. e.g. Refugees migration bringing infectious disease to their new places. When host susceptibility and response are modified by natural or drug-induced immunosuppressant (cancer treatment), malnutrition or diseases such as AIDS.
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Why is it important to investigate outbreaks? Identify the source of infections To prevent, control and contain infectious disease outbreaks To reduce morbidity and mortality due to infectious disease outbreaks To strengthen public health infectious disease surveillance To provide general guidelines and develop a mechanism for effective implementation of outbreak management To describe new diseases and learn more about known diseases To evaluate existing prevention strategies, e.g. vaccines To teach (and learn) epidemiology To address public concern about the outbreak Political and legal concerns
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Sequence of Events in outbreak detection and confirmation (I) Primary Case 1st case at HC Report to DMO Lab result Samples taken Response begins DAY CASES Opportunity for control
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Sequence of events in outbreak detection and confirmation (II) PRIM HC REP RES SAM Response begins DAY CASES Potential Cases Prevented
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Steps in Outbreak Investigation
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STEPS IN OUTBREAK INVESTIGATION Prepare for field work Establish the existence of an outbreak Verify the diagnosis Define and identify cases Line listing method for cases Describe Outbreak/ Descriptive Epidemiology Develop hypotheses Evaluate hypotheses Refine hypotheses and carry out additional studies Implement control and prevention measures Communicate findings
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Specific demands when investigating outbreaks Unexpected event Need to act quickly Need for rapid control Work carried out in the field Systematic approach
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Is this an outbreak? Detection Routine surveillance Clinical / Laboratory General public Media
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Outbreak confirmed Further investigation? Immediate control measures?
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Unknown aetiology (pathogen/source/transmission) Cases serious Cases still occurring Public pressure Training opportunity Scientific interest Outbreak confirmed Further investigation? Prophylaxis Exclusion / isolation Public warning Hygienic measures Immediate control measures?
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Outbreak Investigation Team?
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Coordination Epidemiology Education Clinicians Laboratory Media Authorities Diagnostic Clinical Specimen transfer Dead Sick Exposed Surveillance Investigation Prediction Health personnel Special groups General population Decisions Infrastructure Regulations Vaccinations etc Vector Reservoir
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PREPARE FOR FIELD WORK Research the disease and gather the supplies and equipment needed. Get local contacts. Make a necessary administrative and personal arrangement.
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Establish the existence of an outbreak Determine the expected number of cases for the area in the given time frame. Then observed number of cases which exceeds the expected number The sources of the data vary: Health department surveillance records. Data from local sources such as hospital discharge Records, death (mortality) records, and cancer or birth defect registries. Even if the current number of reported cases exceeds the expected number, the excess may not necessarily indicate an outbreak. Changes in local reporting procedures, Changes in the case definition Increased interest because of local or national awareness Improvements in diagnostic procedures
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VERIFY THE DIAGNOSIS Confirm the diagnosis. Signs Symptoms Test results Stool examination eg: infection with E. coli O157:H7 Lab: Culture, PCR, Serology eg: shigella Radiology/Sputum eg: TB Make sure a +ve test was truly +ve test
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DEFINE AND IDENTIFY CASES Case Definition A definition of a disease that allows a simple, uniform way to identify cases Distinguishes cases from unaffected members of population Develop a SPECIFIC CASE DEFINITION using: Symptoms, signs and lab results Time period Location – need to be specific enough not to include endemic disease
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E.g. Infection with E. coli: Incubation period for E. coli O157:H7 ranges from 3-8 days with a median of 3-4 days. Symptoms are severe bloody diarrhea and abdominal cramps. Positive stool test
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Categories of Cases: Possible/Suspected: Symptoms reported but not confirmed No lab or epidemiological link Probable: Symptoms confirmed No lab or epidemiological link Confirmed: Symptoms characteristic of the agent Lab test confirmed Epidemiological link present
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LINE LISTING Traditionally data are collected on a standard case report form, questionnaire or data abstraction form. Then the critical items are selected on a form called a line listing for analysis, manipulation or cross -tabulation and further use in the investigation.
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Line listing includes important variables, such as name or identification number ID, age, sex, case classification etc. New cases are added to a line listing as they are identified. Thus; a line listing contains key information on every case, and can be scanned and updated as necessary.
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UPDATE THE LINE LIST GIVEN BELOW TO BE CURRENT UP UNTIL THE AFTERNOON OF JULY 18 F: Fever; C: Cough; D: Diarrhea; S: Shortness of breath; M: Myalgia; URI – upper respiratory infection DG: Dava Ghar PJ: Pelu Jaghai JULY 16th, PM
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Line List: July 20th F: Fever; C: Cough; D: Diarrhea; S: Shortness of breath; M: Myalgias; URI – upper respiratory syx DG: Dava Ghar PJ: Pelu Jaghai
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Reminder of the Line list F: Fever; C: Cough; D: Diarrhea; S: Shortness of breath; M: Myalgia; URI – upper respiratory syx DG: Dava Ghar PJ: Pelu Jaghai JULY 20th, PM
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Human-to-Human Transmission Criteria Well documented exposure to a confirmed, probable, or suspect human case AND The time interval between contact with a human case and illness onset is 7 days or less AND Absence of an alternative source of exposure such as exposures to birds, animals, feathers, droppings, fertilizers made of fresh bird droppings, contaminated environments, or laboratory specimens OR Several generations of transmission linked to a primary case 33
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DESCRIBE OUTBREAK DESCRIPTIVE EPIDEMIOLOGY 3 aspects to consider when describing an outbreak: Person: Define by personal characteristics: age, sex, ethnicity etc Define by exposure to risk factors: occupation, diet Place: Where were they infected? Create topographic map with case distribution Time: When were they infected? Create an epidemic curve using various time intervals based on incubation period. Determine type of outbreak (point source, propagated)
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DISTRIBUTION OF CASES OF CHOLERA, LONDON 1854
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DEVELOP HYPOTHESES Using data from the epidemic curve, literature, etc. Form a hypothesis regarding: Type of epidemic: point source or propagated Source of the epidemic: common source, multiple exposure etc. Reservoir Mode of spread and risk factors Details of the illness with date of onset, duration, time of exposure, incubation period and severity of symptoms.
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EVALUATE HYPOTHESES Cohort Study Compare exposed persons with non exposed persons Calculate attack rates in exposed and compare with attack rate in unexposed (relative risk) Case-control study Cases (ill patients) are compared to controls (well patients) The proportion in each group exposed to various risk factors are compared Is the association statistically strong (Chi squared or Fishers exact)? Calculate odds of eating item X and compare odds of ill Vs well (odds ratio)
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REFINE HYPOTHESES AND CARRY OUT ADDITIONAL STUDIES Microbiological investigation Environmental investigation Veterinarian investigation Trace back investigations (origin of foods) Meteorological data Entomological investigations
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IMPLEMENT CONTROL AND PREVENTION MEASURES CONTROL MEASURES Vaccination, medication or prophylaxis PPE – respirator, glasses, mask, gown, latex gloves etc. Isolation/quarantine Educate/Communication Might also implement control measures effectively at an earlier stage of the investigation Do not delay control measures in order to investigate the cause of the outbreak Continue control measures while investigating the possible cause
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COMMUNICATE FINDINGS Identify a single member of the investigation team to interact with media and communicate progress and findings Summarize investigation, make recommendations, and disseminate report to all participants Publication
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Outbreak investigation epidemic curve & formaT of report
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CHARACTERIZE THE DISTRIBUTION OF CASES BY THE EPIDEMIOLOGICAL TRIAD OF DISRIBUTION - PERSON - PLACE AND - TIME.
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TIME VARIABLE Used to construct an epidemic curve – that is graph showing the distribution of cases by date of onset in hours, days, weeks, or months. The shape of the curve may suggest either a common-source outbreak or person-to-person transmission.
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EPIDEMIC CURVE Used to describe the distribution of cases during short periods of time Helpful in determining the source of infection and the possible mode of transmission
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If all cases occur within one incubation period of the disease, it suggests a point source of exposure. If the cases occur over several incubation periods, it suggests either person-to-person transmission or a continuing common source of exposure. If the IP of the disease is known, the curve could tell the probable time and possible source of infection. If the time of exposure can be determined, the IP of the disease can be determined.
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Types of Outbreaks Three types of outbreaks: (1) Common-source Results from exposure of a susceptible group of people to a common agent of disease (a) Point source outbreak (b) Continuing source outbreak (c) Intermittent source outbreak (2) Propagated source (3) Mixed sources
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EPICURVES hours cases cases cases days weeks Common point source Common persistent source Propagated source
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(1)COMMON SOURCE EPIDEMIC (a).Point Source Outbreak Duration of exposure to the common agent is relatively brief. Epidemic curve Rapid rise in no. of cases Hits a peak level No secondary waves Followed by a gradual decline Short-lived All cases develop disease within one IP
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(b).Continuing Source Outbreak Exposure to the common agent of disease is prolonged beyond a brief period Exposure is not simultaneous Epidemic curve Rapid rise in no. of cases Reach a plateau Followed by gradual decline Last longer than time range of incubation period
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(c)Intermittent Source Outbreak Exposure to the common source of disease is irregular Epidemic curve Small clusters or individual cases spread over a relatively protracted time period See gaps
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(2) PROPAGATED EPIDEMIC due to direct person-to-person transmission Or by indirect transmission through vector
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Epidemic curve Relatively gradual rise in no. of cases Steep decline May be more than 1 peak Additional peaks represent secondary and tertiary spread of disease longer duration than those for common-source outbreaks cases
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(3) Mixed Outbreaks Combination of common source and propagated outbreaks Often begin with common source exposure that is followed by person-to-person spread Epidemic curve Single large peak Subsequent smaller peaks
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cases exposure ESTIMATION OF TIME OR PERIOD OF EXPOSURE
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IN FOOD-BORNE OUTBREAKS The calculation of the incubation period (i.e. the time interval from exposure to onset of clinical disease) can be used to determine the etiologic agent.
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TYPE I EPIDEMIC CURVES Characterized by a rapid rise and fall of cases so that all cases fall within the range of one incubation period. Caused by a common source of exposure at one point in time. If the IP of the disease is known and if all of the cases occur within one IP, the days can be counted backward and the source of infection determined.
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Example (show the epidemic curve describing an outbreak of Infectious Hepatitis in Ogemaw Country, Michigan.
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FINDINGS One of the two cases that occurred in early April was responsible for the subsequent 61 cases. The other case was unrelated to this outbreak. The curve suggests a common-source outbreak since all of the cases fall within a 30-day period, which is consistent with the known IP for hepatitis A (i.e., 15-50 days; average 25-30 days) The cases were epidemiologically linked to the index case (onset April 6) who prepared glazed doughnuts and applied icing to pastry.
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TYPE II, OR PROPAGATED EPIDEMIC CURVE Characterized by cases occurring over more than one IP of the disease. The shape of the curve suggests either person-to-person transmission or a continuing common-source outbreak.
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Example, shows the epidemic curve describing an outbreak of viral hepatitis A transmitted from person -to -person
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An outbreak report
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Writing the report The report should be complete and convincing. Information to be included in the final report on an epidemic is given as follow: 1. BACKGROUND geographical location climatic conditions Demographic status (population pyramid) socioeconomic situation organization of health services surveillance and early warning systems normal disease prevalence
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2. HISTORICAL DATA previous occurrence of epidemics *of the same disease, *locally or elsewhere occurrence of related diseases, if any *in the same area *in other area discovery of the first cases of the present outbreak
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3. Methodology of investigations Case definition Questionnaire used in epidemiological investigation Survey teams *household survey *retrospective survey *prospective surveillance *collection of laboratory specimens *laboratory techniques
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5. ANALYSIS OF DATA Clinical data *frequency of signs and symptoms *course of disease *differential diagnosis *death or sequelae rates Epidemiological data *mode of occurrence *in time *by place *by population groups
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Interpretation of data *comprehensive picture of the outbreak *hypotheses as to cause(s) *formulation and testing of hypotheses by statistical analysis
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Modes of transmission *source(s) of infection *route(s) of excretion and portal(s) of entry *factors influencing transmission Laboratory data *isolation of agent(s) *serological confirmation *significant of results
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5. CONTROL MEASURES Definition of strategies and methodology of implementation *constraints *results Evaluation *significance of results *cost/effectiveness Preventive measures
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Implement control measures May occur at any time during the outbreak!! Prevent recurrence Control the source of the pathogen Interrupt transmission Modify host response
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Control the source of pathogen Remove source of contamination Remove persons from exposure Inactivate / neutralise the pathogen Isolate and/or treat infected persons Quarantine the contacts
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INTERRUPT TRANSMISSION Interrupt environmental sources Control vector transmission Improve personal sanitation
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MODIFY HOST RESPONSE Immunise susceptible Use prophylactic chemotherapy
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FINALLY Prepare written report Communicate public health messages Influence public health policy Evaluate performance
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Notifiable diseases in Malaysia
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Disease Control Division Ministry of Health National Notification of Infectious Diseases System AIDS/STD Surveillance System Vector-borne Diseases Surveillance System HMIS Sentinel Surveillance Ad-hoc survey Laboratory network Overseas Data Special Surveillance Current Surveillance Systems Syndromic Approach Surveillance
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DEFINITION OF NOTIFIABLE DISEASE Disease that by statutory requirements must be reported to the public health authority in the pertinent jurisdiction when the diagnosis is made. - WHO-
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Characteristics of notifiable disease Potential to spread internationally (spreads rapidly ). eg. plague Seriousness of the public health impact of the event Life threatening and not easily treated/cured Used to monitor development of community outbreaks or success of immunization program Example : polio, measles
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Unusual or unexpected nature of the event. eg. Food poisoning The risk that restrictions to travel or trade may result because of the event. eg. Cholera, Plague, Yellow fever
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Source :MOH
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Source :MOH
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Source :MOH
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Source :MOH
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ASSIGNMENT Define Epidemiology , epidemic, endemic, pandemic Define Outbreak ,and explain its difference with Epidemic . Explain Case definition & Categories of cases Describe Line listing of cases & its uses Describe steps for outbreak investigation Explain epidemic investigation and descriptive epidemiology of an outbreak reporting What are Epidemic Curves? Explain with examples. Discuss prevention & control measures of outbreak in general List Notifiable Diseases and describe its purpose.
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Thank you Any questions?