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Outbreak Management

Outbreak Management. 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. Time involved. 6 0 minutes. Purposes of Outbreak Investigation.

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Outbreak Management

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  1. OutbreakManagement

  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.

  3. Time involved 60 minutes

  4. Purposes of Outbreak Investigation To Identify the causal agent To 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 transmission

  5. Definitions - 1 • Outbreak or epidemic • An excess over the expected (usual) level of a disease within a geographic area • However, one case of an unusual disease may constitute an epidemic • E.g., postsurgical group A streptococcus infection

  6. Definitions - 2 • Endemic • The usual level of a disease within a geographic area • E.g., a hospital • These ‘sporadic’ infections represent most preventable healthcare-associated infections • Baseline incidence • Pandemic • An epidemic that spreads in several countries • Usually affecting many people

  7. Endemic and Epidemic Number of Cases of Disease “Endemic” “Epidemic” Time

  8. Healthcare-associated infections Majority of healthcare-associated infections are endemic Outbreak of healthcare-associated infections occur typically in a specific group of patients

  9. Definitions - 3 • Relative risk • Ameasure of association between a disease or condition and a factor under study • Calculation • Divide the incidence rate of those exposed to the factor by the incidence rate of those not exposed

  10. Interpretation of Relative Risk

  11. Types of Outbreaks • Community-acquired • Food-borne infections, measles • Healthcare-associated • When two or more cases of infection appear to be epidemiologically related

  12. Steps of Outbreak Investigation Verify existence of the outbreak Determine if there were changes in case finding or diagnostics Establish diagnosis of reported cases Case finding Characterise cases Formulate hypothesis Test the hypothesis Institute control measures and follow up

  13. Verify existence of an outbreak • Compare 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 situation

  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 identified Provides a new ‘baseline’ of disease

  15. Define cases • Typically involves identifying an agent • Define cases based on the following common factors: • Population risk factors • Age, race, sex, socioeconomic status • Clinical data • Onset of signs and symptoms • Frequency and duration of clinical features associated with the outbreak • Laboratory results

  16. Case Definition The inclusion and exclusion criteria for cases must be precisely identified The definition should differentiate between infection and colonisation Includes a unit of time and place and specific biological and/or clinical criteria A graded definition (definite, probable, or possible) often helps

  17. Case Finding Collect critical data and specimen information from: • Laboratory reports • Medical records • Patient charts • Physicians and nursing staff • Public health data

  18. Characterise cases Assemble and organise available information for analysis From this information, the population at risk can be accurately described

  19. Characterise cases - Time • The exact period of the outbreak • The probable period of exposure • Date of onset of illness for cases; draw an epidemic curve • Is the outbreak common source or propagated?

  20. Characterisecases – Place/Time Place • Service, ward, operating room • Clustering of cases Person • Patient characteristics (age, sex, underlying disease) • Possible exposures (surgery, nursing and medical staff , infected patients) • Therapy (invasive procedures, medications, antibiotics)

  21. Calculate rates • Incidence rate • The 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 time • Attack rate • The cumulative incidence rate of infection in a group over a period of an epidemic • Number of people at risk who are infected / Total number of people at risk

  22. Source of Infection • Common source (single-point source) • Same origin • Propagated or continuing source (on-going transmission) • Infections are transmitted from person to person • Both common and propagated source • Intermittent exposure to a common source • Produces an epidemic curve with irregularly spaced peaks

  23. Epidemic curve - 1 Also called a histogram Determines the character of an epidemic Cases are plotted by date of onset of illness Time 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 distributed

  24. Epidemic curve - 2 The reasons for constructing an epidemic curve include: • To determine whether the source of infection was common, propagated, or both • To identify the probable time of exposure of the cases to the source(s) of infection • To identify the probable incubation period • To determine if the problem is ongoing

  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.

  26. Epidemic curve • Helps to develop hypotheses • Incubation period • Etiological agent • Type of source • Mode of transmission • Propagated source • Common source • Time of exposure

  27. Common Source Outbreak

  28. An explosive epidemic of short duration generally indicates A common source of infection Exposure over a short period of time A large numbers of susceptible exposed A high attack rate An incubation period with little variation

  29. Propagated Source Outbreak • Cases occur over a long period • Explosive epidemics due to person-to-person transmission may occur • E.g., chickenpox • If secondary and tertiary cases occur, intervals between peaks usually approximate to the average incubation period

  30. Propagated source - 1 Single exposure, no secondary cases (e.g. measles)

  31. Propagated source - 2 Secondary and tertiary cases (e.g., hepatitis A)

  32. Determine Exposure Period • Using the mean or median incubation period • Identify the peak of the epidemic or the date of onset of the median case • Count back into one incubation period • Using minimum and maximum incubation periods • Start with the first case identified and count back in time the minimum incubation period • Then using the last case, count back in time the maximum incubation period

  33. Exposure Period

  34. Formulate hypothesis Make a best guess to explain the observations The hypothesis should explain most cases

  35. Test the Hypothesis Many investigations do not reach this stage Investigation may end with descriptive epidemiology and then the problem goes away without intervention or does not require a special study

  36. Institute Control Measures Control 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 observations

  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 food • Remove persons from exposure • Keep people from being exposed to mosquito bites to prevent encephalitis

  38. Healthcare-Associated Infections – Control Measures

  39. Evaluate Efficacy of Control Measures • Cases cease to occur or return to endemic level • No change (re-evaluate cases)

  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 investigation • It should include recommendations to prevent any future occurrence

  41. Summary • Outbreaks 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 image • Proper steps and effective techniques should be used to investigate a suspected outbreak • Clear recommendations should be formulated to prevent further transmission and/or outbreaks

  42. References Flora 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.htm

  43. Web Resource • How to Investigate an Outbreak • http://www.cdc.gov/excite/classroom/outbreak/index.htm • Communicable Disease Control: Outbreak Investigation • http://www.healthknowledge.org.uk/public-health-textbook/disease-causation-diagnostic/2g-communicable-disease/outbreak-investigation • Epidemiological Investigation of Outbreaks • http://www.gov.mb.ca/health/publichealth/cdc/protocol/investigation.pdf

  44. Quiz • Outbreak investigations are performed primarily to: • Gather clinical information about a disease • Find the source of infections • Make sure patients are treated • All of the above • Epidemic curves help determine if the problem is on-going. T/F • Control measures for healthcare-associated infections include all except: • Patient isolation • Use of disposables • Hand hygiene • Immunisation

  45. International Federation of Infection Control IFIC’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/

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