The document outlines the key principles and steps of conducting an outbreak investigation. It defines what constitutes an outbreak and explains that the purpose is to control the current outbreak, prevent future occurrences, and evaluate existing surveillance and prevention programs. The main steps described are confirming the outbreak, defining cases, collecting descriptive data, developing hypotheses, testing hypotheses through analytical studies, communicating conclusions, and recommending control measures.

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.

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

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

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

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

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

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

74. Place data Mapping Locations Distribution Spreading of the disease

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

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