Describe the occurrence of disease in a population Discuss how an epidemic curve can help in managing an outbreak Outline the steps in outbreak investigation 2 December 1 2013 Time involved ID: 1042424
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1. Outbreak Management
2. Learning Objectives Describe the occurrence of disease in a population.Discuss how an epidemic curve can help in managing an outbreak.Outline the steps in outbreak investigation.2December 1, 2013
3. Time involved60 minutesDecember 1, 20133
4. Purposes of Outbreak InvestigationTo Identify the causal agentTo find the source of infection by studying the occurrence of the disease among persons, place, or time, as well as determining specific attack rates Formulate recommendations to prevent further transmission4December 1, 2013
5. Definitions - 1 Outbreak or epidemicAn excess over the expected (usual) level of a disease within a geographic areaHowever, one case of an unusual disease may constitute an epidemicE.g., postsurgical group A streptococcus infectionDecember 1, 20135
6. Definitions - 2 EndemicThe usual level of a disease within a geographic area E.g., a hospitalThese ‘sporadic’ infections represent most preventable healthcare-associated infectionsBaseline incidence PandemicAn epidemic that spreads in several countriesUsually affecting many peopleDecember 1, 20136
7. Endemic and Epidemic“Endemic”“Epidemic”TimeNumber of Casesof Disease7December 1, 2013
8. Healthcare-associated infectionsMajority of healthcare-associated infections are endemicOutbreak of healthcare-associated infections occur typically in a specific group of patientsDecember 1, 20138
9. Definitions - 3 Relative riskA measure of association between a disease or condition and a factor under studyCalculationDivide the incidence rate of those exposed to the factor by the incidence rate of those not exposedDecember 1, 20139
10. Interpretation of Relative RiskRR =1Incidence in the exposed group is the same as in the non-exposedThere is no association between exposure and diseaseRR >1 Denotes a larger incidence in the exposed than in the non-exposedExposure seems to increase the probability of developing the diseaseRR <1 Denotes a smaller incidence in the exposed than in the non-exposedExposure seems to decrease the probability of developing the disease10December 1, 2013
11. Types of Outbreaks Community-acquiredFood-borne infections, measlesHealthcare-associatedWhen two or more cases of infection appear to be epidemiologically related11December 1, 2013
12. Steps of Outbreak InvestigationVerify existence of the outbreakDetermine if there were changes in case finding or diagnostics Establish diagnosis of reported cases Case findingCharacterise cases Formulate hypothesisTest the hypothesis Institute control measures and follow up 12December 1, 2013
13. Verify existence of an outbreakCompare the number of current cases with the usual baseline incidence from previous months or years If local data are not available, compare to information from national surveillance systems or the literature these data may not be applicable to the local situation13December 1, 2013
14. Determine if there were changes in case finding or diagnostics New techniques or laboratory tests may increase identification when historically cases would not have been identifiedProvides a new ‘baseline’ of disease 14December 1, 2013
15. Define casesTypically involves identifying an agentDefine cases based on the following common factors:Population risk factorsAge, race, sex, socioeconomic statusClinical dataOnset of signs and symptomsFrequency and duration of clinical features associated with the outbreakLaboratory resultsDecember 1, 201315
16. Case Definition The inclusion and exclusion criteria for cases must be precisely identified The definition should differentiate between infection and colonisationIncludes a unit of time and place and specific biological and/or clinical criteria A graded definition (definite, probable, or possible) often helps16December 1, 2013
17. Case FindingCollect critical data and specimen information from: Laboratory reports Medical recordsPatient chartsPhysicians and nursing staffPublic health dataDecember 1, 201317
18. Characterise casesAssemble and organise available information for analysisFrom this information, the population at risk can be accurately describedDecember 1, 201318
19. Characterise cases - TimeThe exact period of the outbreakThe probable period of exposureDate of onset of illness for cases; draw an epidemic curveIs the outbreak common source or propagated? 19December 1, 2013
20. Characterise cases – Place/TimePlaceService, ward, operating roomClustering of casesPersonPatient characteristics (age, sex, underlying disease)Possible exposures (surgery, nursing and medical staff , infected patients)Therapy (invasive procedures, medications, antibiotics)December 1, 201320
21. Calculate ratesIncidence rateThe number of new cases occurring in the population during a specified time / number of persons exposed to the risk of developing the disease during that timeAttack rateThe cumulative incidence rate of infection in a group over a period of an epidemicNumber of people at risk who are infected / Total number of people at riskDecember 1, 201321
22. Source of Infection Common source (single-point source)Same originPropagated or continuing source (on-going transmission)Infections are transmitted from person to personBoth common and propagated sourceIntermittent exposure to a common source Produces an epidemic curve with irregularly spaced peaks22December 1, 2013
23. Epidemic curve - 1 Also called a histogramDetermines the character of an epidemic Cases are plotted by date of onset of illnessTime intervals (on the X axis) are based on the incubation or latency period of the disease and the length of the period over which cases are distributed23December 1, 2013
24. Epidemic curve - 2The reasons for constructing an epidemic curve include:To determine whether the source of infection was common, propagated, or bothTo identify the probable time of exposure of the cases to the source(s) of infectionTo identify the probable incubation periodTo determine if the problem is ongoing24December 1, 2013
25. A . Propagated source: single exposure, no secondary cases (e.g., measles).B. Propagated source: secondary and tertiary cases (e.g., hepatitis A).Common source: point exposure . Common source: Intermittent exposure.25December 1, 2013
26. Epidemic curve26Helps to develop hypothesesIncubation periodEtiological agentType of sourceMode of transmissionPropagated sourceCommon sourceTime of exposureDecember 1, 2013
27. Common Source Outbreak27December 1, 2013
28. An explosive epidemic of short duration generally indicatesA common source of infectionExposure over a short period of timeA large numbers of susceptible exposedA high attack rateAn incubation period with little variationDecember 1, 201328
29. Propagated Source OutbreakCases occur over a long periodExplosive epidemics due to person-to-person transmission may occurE.g., chickenpoxIf secondary and tertiary cases occur, intervals between peaks usually approximate to the average incubation period29December 1, 2013
30. Propagated source - 1December 1, 201330Single exposure, no secondary cases (e.g. measles)
31. Propagated source - 2December 1, 201331Secondary and tertiary cases (e.g., hepatitis A)
32. Determine Exposure PeriodUsing the mean or median incubation periodIdentify the peak of the epidemic or the date of onset of the median caseCount back into one incubation periodUsing minimum and maximum incubation periodsStart with the first case identified and count back in time the minimum incubation periodThen using the last case, count back in time the maximum incubation periodDecember 1, 201332
33. Exposure Period33December 1, 2013
34. Formulate hypothesisMake a best guess to explain the observationsThe hypothesis should explain most cases34December 1, 2013
35. Test the Hypothesis Many investigations do not reach this stageInvestigation may end with descriptive epidemiology and then the problem goes away without intervention or does not require a special study35December 1, 2013
36. Institute Control MeasuresControl measures are determined by the results of the initial analysis in consultation with appropriate professionals They will vary depending on the agent, the mode of transmission, and observations36December 1, 2013
37. Control Measures Interventions commonly used to control an outbreak are as follows:Control the source of the pathogen Remove the source of contamination, e.g., discard contaminated foodRemove persons from exposureKeep people from being exposed to mosquito bites to prevent encephalitisDecember 1, 201337
38. Healthcare-Associated Infections – Control MeasuresType of transmission suspectedSuggested actionContact- Cross-transmission (transmission between individuals)Patient isolation and barrier precautions determined by infectious agent(s)Contact- Hand transmissionImprovements in hand hygiene (e.g., washing, disinfection, glove use)Airborne agent Patient isolation with appropriate ventilation Waterborne agent Checking of water supply and all liquid containers Use of disposable devicesFoodborne agent Elimination of the at-risk food December 1, 201338
39. Evaluate Efficacy of Control Measures Cases cease to occur or return to endemic levelNo change (re-evaluate cases)39December 1, 2013
40. Communicate and Write a Final Report During the investigation, up-to-date information is communicated to administration and appropriate authorities A final report should be prepared describing the outbreak, interventions, and effectiveness, and summarising the contribution of each team member participating in the investigationIt should include recommendations to prevent any future occurrence40December 1, 2013
41. SummaryOutbreaks of infection should be clearly defined, identified, and promptly investigated because of their importance in terms of morbidity, cost, improvement of patient care, and institutional imageProper steps and effective techniques should be used to investigate a suspected outbreakClear recommendations should be formulated to prevent further transmission and/or outbreaksDecember 1, 201341
42. ReferencesFlora IH, Manuel B. Disease Outbreak Investigation. The Young Epidemiology Scholars Program (YES) supported by The Robert Wood Johnson Foundation and administered by the College Board, 2005. http://www.collegeboard.com/yes/ft/iu/home.html Reingold AL. Outbreak Investigations—A Perspective. National Center for Infectious Diseases, Centers for Disease Control and Prevention. Emerg Infect Diseases 1998; 4 (1). http://www.cdc.gov/ncidod/eid/vol4no1/reingold.htm Susan P. Outbreak Investigation. The University of Texas, Harris county psychiatric center, 2010. http://www.uth.tmc.edu/uth_orgs/hcpc/procedures/volume1/chapter6/infection_control-51.htmDecember 1, 201342
43. Web ResourceHow to Investigate an Outbreakhttp://www.cdc.gov/excite/classroom/outbreak/index.htm Communicable Disease Control: Outbreak Investigationhttp://www.healthknowledge.org.uk/public-health-textbook/disease-causation-diagnostic/2g-communicable-disease/outbreak-investigation Epidemiological Investigation of Outbreakshttp://www.gov.mb.ca/health/publichealth/cdc/protocol/investigation.pdf December 1, 201343
44. QuizOutbreak investigations are performed primarily to:Gather clinical information about a diseaseFind the source of infectionsMake sure patients are treatedAll of the aboveEpidemic curves help determine if the problem is on-going. T/FControl measures for healthcare-associated infections include all except:Patient isolationUse of disposablesHand hygieneImmunisation December 1, 201344
45. International Federation of Infection ControlIFIC’s mission is to facilitate international networking in order to improve the prevention and control of healthcare associated infections worldwide. It is an umbrella organisation of societies and associations of healthcare professionals in infection control and related fields across the globe . The goal of IFIC is to minimise the risk of infection within healthcare settings through development of a network of infection control organisations for communication, consensus building, education and sharing expertise. For more information go to http://theific.org/December 1, 201345