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Outbreak Investigation

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  • 1.  
  • 2.
  • 3. Outbreak Investigation COL.POTE AIMPUN, MD., Dr.PH Medical Specialist Office for Medical Services Office of Permanent Secretary of Defense
  • 4. Contents
    • Definition of outbreak
    • Purpose of outbreak investigation
    • Principles and steps of an outbreak investigation
  • 5. Definition of outbreak
    • The occurrence of cases of an illness, specific health-related behavior, or other health-related events clearly in excess of normal expectancy. ( >Mean +2SD) The area and the period in which the cases occur are specified precisely
    • Adapted from WHO recommended surveillance standards, 2 nd edition, 1999
  • 6. Outbreak Investigation
    • Processes of finding cause(s) of an epidemic by collecting, analyzing the data to propose the control program(s) of this outbreak and to prevent the future one.
    • The prevention and control program is the outcome of the finding about time place and person of what when where why and how.
  • 7.
  • 8. Judged to be an outbreak A greater number of cases than normally occur in the same place compare to the same period of time
  • 9. Meningococcal Epidemic Curve July '96 - June '98, Ireland
  • 10. Judged to be an outbreak A cluster of cases which can be linked to the same exposure. The number of meningococcal cases associated with pilgrims who have traveled for the Haj has increased, and the total number of cases to date is 14 including 4 death Judged to be an outbreak A single case of disease that has never been occurred . A 3 year old boy, case of Avian flu (HSN1), alerted the public health people around the world to start a full scale investigation
  • 11.
  • 12.
  • 13. Routine Surveillance Health personnel Laboratory General public Media Detection of Outbreak
  • 14. Purpose of outbreak investigation
    • To control current outbreak
    • To prevent occurrence of future outbreak
    • Research for more knowledge of the disease
    • To evaluate the effectiveness of prevention program
    • To evaluate the effectiveness of the existing surveillance
    • To train health professional
  • 15.
  • 16.
  • 17. Special circumstance for outbreak
    • Unexpected event
    • Emergency situation
    • Urgency for control
    • Field work
    • Systematic approach
  • 18. Types of outbreak
    • Individual case investigation
    • Outbreak investigation
  • 19. Individual case investigation
    • Objectives
      • Confirm an outbreak
      • Prevent spreading of disease
      • Natural history of the disease in individual
  • 20. Individual case investigation
    • Steps in invest igation
      • Patient data collection
      • Determine the spreading of the disease
      • Specimen collection
      • Disease control
      • Writing a report
  • 21. Patient data collection
    • History taking
    • Diagnosis
    • Laboratory
    • Environmental survey
    • Other epidemiological factors
    Environment Host Agent
  • 22. Determine the spreading of the disease
    • Contact
      • Family
      • Villagers
      • Work place
    • Other patients
  • 23. Specimen collection
    • Contacts
    • Environment
    • Index case
      • What specimen?
      • Where to collect?
      • How to send the specimen?
  • 24. Specimen collection
    • What to collect
    • Where to collect
    • When to collect
    • What kind of container
    • Media
    • Transportation
    • Patient data detail
  • 25. Disease control
    • Area of contamination
    • Contactors
    • Pathogen destruction
    • Control of spreading
  • 26. Writing report(s)
    • Introduction
    • Investigation report
    • Control activities that have been done
    • Tendency of epidemics
    • Important and emergency to Public health
    • Recommendations
  • 27. Diseases
    • Cholera
    • Severe acute diarrhea
    • Polio, Diphtheria , Whooping cough , Tetanus
    • Rabies
    • Measles in IPD
    • Other interesting disease
  • 28.
  • 29. Types of outbreak
    • Individual case investigation
    • Outbreak investigation
  • 30. Outbreak investigation
    • More than mean (>2 SD)
    • Common exposure
    • Never occur in the area before
  • 31. Types of epidemics
    • Common source epidemics
    • Propagated source epidemics
  • 32. Common source epidemics
    • Group of people
    • Common exposure of pathogen
    • Short incubation period
    • Etc. food poisoning, hepatitis for common needle user
  • 33. Common source outbreak
  • 34. Epidemic curve Sick date Exposure date Number of patients
  • 35. Propagated source epidemics
    • Person
    • Individual contact
    • Spreading in community
    • Etc. influenza in household, tuberculosis in factory
  • 36. Propagated source epidemics
  • 37. Epidemic Curve Propagated source epidemics Sick date Number of patients
  • 38. Epidemic curve Sick date Exposure date Number of patients
    • Axis X: Times
    • Axis Y: Patients
  • 39. Epidemic curve
    • Type of epidemics
    • Estimate exposure period to calculate incubation period
    No. Pt. Sick date (Point source outbreak) Min. IP Max. IP Median. IP 0 1 2 3 4 5 6 7 8 9 10
  • 40. Compare Common Source Propagated source 1.Curve Bell curve Scatter bell 2.First and last pt. < 1 IP > 1 IP 3.Transmission One source From person to person 4.Duration Short Long 5. control Eradicate source Health education
  • 41. Steps of an outbreak investigation
    • Field work preparation
    • Confirm outbreak and diagnosis
    • Define case and start case-finding
    • Descriptive data collection and analysis
    • Develop hypothesis
    • Analytic study to test hypotheses
    • Special study (environmental study)
    • Communicate the conclusion and recommend control measures
    • Follow-up the control implementations
    • Outbreak investigation Report
  • 42. Field work preparation
    • Knowledge of the disease
    • Team
      • Epidemiologist
      • Health educator
      • Laboratory technician
      • Specialist
    • Coordinate with local authorities
  • 43. Confirm outbreak and diagnosis
    • Signs, symptoms and laboratory
    • In undiagnosed disease
      • Definite diagnosis must be done
    • Confirm that this is a real outbreak
    • Must gather information from local authorities to conclude that this is an outbreak and must start an investigation
  • 44. Define case and start case-finding
    • Must comply to clinical
    • Easy to diagnose
    • Sense and Specificity
    • Finding cases
      • Passive case detection:
        • From hospital or clinic
        • Seriously ill
      • Active case detection
        • From community
        • Subclinical
  • 45. Iceberg Phenomenon Hosp. visit w symptoms No symptoms Infected Risk Diagnosed
  • 46. Case definition
    • Standard set of criteria to identify cases
    • Clinical criteria restriction of time, place, person
    • Simple, practical, objective
    • Sensitivity vs. specificity
    • Example
      • Patient older than 5 years with severe dehydration or dying of acute watery diarrhea in town “A” between 1 January and 1 June 2002
  • 47. Case definiteion
    • Possible/Suspected
      • Symptoms/signs not clear
    • Probable
      • Dx from Hx and PE
    • Confirmed
      • Dx from Hx, PE and laboratory testing
  • 48. Case definiteion
    • Possible/Suspected
      • Severe diarrhea
    • Probable
      • 5 y/o with severe diarrhea and dehydration
    • Confirmed
      • Positive culture for Vibrio cholera 0139
      • Normally case definition will not contain risk factors
  • 49. Sensitivity and specificity Sensitivity Specificity
  • 50. Test result d c Negative b a Positive No Yes Disease
  • 51. Accuracy
    • Sensitivity
      • Ability of the test to identify correctly those who have the disease
      • Probability of a positive test in people with the disease
  • 52. Test result d c Negative b a Positive No Yes Disease Sensitivity = P(T+|D+) = a /(a+c)
  • 53. Test result d c Negative b a Positive No Yes Disease False-negative rate = P(T-|D+) = c/(a+c) TPF + FNF = 1
  • 54. Accuracy
    • Specificity
      • Ability of the test to identify correctly those who do not have the disease
      • Probability of a negative test in people without the disease
  • 55. Test result d c Negative b a Positive No Yes Disease Specificity = P(T-|D-) = d /(b+d)
  • 56. Test result d c Negative b a Positive No Yes Disease False-positive rate = P(T+|D-) = b/(b+d) TNF + FPF = 1
  • 57. Test result 900 200 Negative 100 800 Positive No Yes Disease Specificity = 800/1000 = 0.8 Specificity = 900/1000 = 0.9 Accuracy = (800+900)/2000 = 0.85 1000 1000
  • 58.
  • 59.
  • 60. Sens. > Spec. Sens. < Spec.
    • Many false positive
    • Many specimens to test
    • Low % tested specimen +VE
    • Overload work
    • Few false positive
    • Fewer specimens to test
    • Higher % tested specimen +VE
    • Too small number of cases
  • 61. Confirm outbreak and diagnosis Is this an outbreak? What is the diagnosis? Link between cases? Higher than expected? Clinical manifestation Laboratory result
  • 62. Scenario
    • Many adults in a remote village were sick with fever, severe joint and muscle pain and rash over the body
    • Is this an outbreak?
    • What is likely diagnosis?
    • Which intervention should be start?
    • Shall we start the investigation?
    • Outbreak confirmed
    • Measles, rubella, dengue
    • Investigation warranted
    • Shall we start vaccine or spray mosquitoes?
  • 63. Outbreak confirmed, further investigation warranted Form outbreak Investigation & control team Epidemiologist Microbiologist Clinician Environmentalist Government Media etc. Team coordinates Field investigation
  • 64. 2. Define case and start case-finding 3. Descriptive data collection and analysis Descriptive epidemiology Person Place Time
  • 65. Identify & count cases Obtain Information Identifying information Demographic data Clinical details Risk factors
  • 66.
  • 67.
  • 68. Identify & count cases Obtain Information Orient cases in -Time -Place -Person Analysis of Descriptive data
  • 69. Demographic data
    • Stratified population data according to gender, age group, jobs
    • Calculate specific attack rate to identify population at risk
  • 70. Dz and rate of measles Age group ( year ) Number of pt. Medical personnel Attack rate (%) male female male female male female 20 - 24 0 1 0 6 0 16.67 25 - 29 0 3 8 29 0 10.34 30 - 34 2 2 8 22 25 9.09 35 - 39 0 1 1 11 0 9.09 40 – 44 0 1 4 4 0 25.00 45 – 49 0 0 3 0 0 0 50 + 0 0 3 2 0 0 Total 2 8 27 74 7.4 10.81
  • 71. Time data
    • Epidemic curve
    • Incubation period
    • Type of epidemics
  • 72.
  • 73.
  • 74. Place data
    • Mapping
    • Locations
    • Distribution
    • Spreading of the disease
  • 75.
  • 76.
  • 77. Cases Evaluate information Pathogen? Source? Transmission? Person Place Time Hypothesis setup : from all the data
  • 78. 5. Develop hypothesis
    • Who is at risk of becoming ill?
    • What is the source and the vehicle?
    • What is the mode of transmission ?
    • Example
      • Tattoo was the risk of getting hepatitis A because 13 of 15 cases had new tattoos.
      • A shallow well was he source of shigellosis because most of cases use water from there.
  • 79. 6. Analytic study to test hypotheses
    • Compare hypotheses with facts
    • Prove hypotheses from descriptive studies
    • Test specific hypotheses with analytic studies between cases and none cases
      • Case-control studies
      • Cohort studies
  • 80.
  • 81.
  • 82. 7. Special studies
    • Laboratory
    • Serology
    • Environmental studies
    • Etc.
  • 83. 8. Conclusion and recommend control measures
    • Control pathogens/agents/causes
      • Destroy sources
      • Emigrate people from sources
      • Diagnoses and identify patients then treatment
    • Stop transmission
      • Vector control
      • Sanitation improvement
      • Health education and information
    • Modified host
      • Vaccination
      • Prophylaxis drug
  • 84. 9. Follow-up the control implementations
    • Assess prevention and control programs
    • Surveillance the future outbreak
  • 85. 10. Outbreak investigation Report
    • Format
      • Introduction
      • Materials and methods
      • Results
      • Prevention and control programs that have been conducted
      • Recommendations
  • 86. 10. Outbreak investigation Report
    • Return the information back to
      • Prevention and control authorities
      • Health personnel
      • Population

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