Disease Outbreak Management Overview
This content covers various aspects of disease outbreak management, including learning objectives, time involved, outbreak investigation steps, and definitions related to outbreaks and epidemics. It discusses the occurrence of diseases in populations, the use of epidemic curves in outbreak management, and the purposes of outbreak investigation. Explore how to identify causal agents, find infection sources, and prevent further transmission. Learn about endemic, epidemic, and pandemic diseases, as well as healthcare-associated infections.
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Presentation Transcript
Outbreak Management
Learning Objectives December 1, 2013 1. Describe the occurrence of disease in a population. 2. Discuss how an epidemic curve can help in managing an outbreak. 3. Outline the steps in outbreak investigation. 2
Time involved December 1, 2013 60 minutes 3
Purposes of Outbreak Investigation December 1, 2013 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 4
Definitions -1 December 1, 2013 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 5
Definitions -2 December 1, 2013 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 6
Endemic and Epidemic December 1, 2013 Number of Cases of Disease Endemic Epidemic Time 7
Healthcare-associated infections December 1, 2013 Majority of healthcare-associated infections are endemic Outbreak of healthcare-associated infections occur typically in a specific group of patients 8
Definitions -3 December 1, 2013 Relative risk A measure 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 9
Interpretation of Relative Risk December 1, 2013 RR =1 Incidence in the exposed group is the same as in the non-exposed Denotes a larger incidence in the exposed than in the non- exposed Denotes a smaller incidence in the exposed than in the non-exposed There is no association between exposure and disease Exposure seems to increase the probability of developing the disease Exposure seems to decrease the probability of developing the disease RR >1 RR <1 10
Types of Outbreaks December 1, 2013 Community-acquired Food-borne infections, measles Healthcare-associated When two or more cases of infection appear to be epidemiologically related 11
Steps of Outbreak Investigation December 1, 2013 1. Verify existence of the outbreak 2. Determine if there were changes in case finding or diagnostics 3. Establish diagnosis of reported cases 4. Case finding 5. Characterise cases 6. Formulate hypothesis 7. Test the hypothesis 8. Institute control measures and follow up 12
Verify existence of an outbreak December 1, 2013 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 13
Determine if there were changes in case finding or diagnostics December 1, 2013 New techniques or laboratory tests may increase identification when historically cases would not have been identified Provides a new baseline of disease 14
Define cases December 1, 2013 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 15
Case Definition December 1, 2013 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 16
Case Finding December 1, 2013 Collect critical data and specimen information from: Laboratory reports Medical records Patient charts Physicians and nursing staff Public health data 17
Characterise cases December 1, 2013 Assemble and organise available information for analysis From this information, the population at risk can be accurately described 18
Characterisecases -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? December 1, 2013 19
Characterisecases Place/Time December 1, 2013 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) 20
Calculate rates December 1, 2013 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 21
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 December 1, 2013 22
Epidemic curve -1 December 1, 2013 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 23
Epidemic curve -2 December 1, 2013 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 24
December 1, 2013 A . Propagated source: single exposure, no secondary cases (e.g., measles). B. Propagated source: secondary and tertiary cases (e.g., hepatitis A). C. Common source: point exposure . D. Common source: Intermittent exposure. 25
Epidemiccurve December 1, 2013 Helps to develop hypotheses Incubation period Etiological agent Type of source Mode of transmission Propagated source Common source Time of exposure 26
Common Source Outbreak 27 December 1, 2013
An explosive epidemic of short duration generally indicates December 1, 2013 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 28
Propagated Source Outbreak December 1, 2013 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 29
Propagated source -1 December 1, 2013 Single exposure, 8 no secondary cases (e.g. measles) 7 6 5 Cases 4 3 2 1 0 1 2 3 4 5 6 7 8 9 10 11 12 30 Week
Propagated source -2 Secondary and tertiary cases (e.g., hepatitis A) December 1, 2013 10 9 8 7 6 Cases 5 4 3 2 1 0 1 2 3 4 5 6 7 8 9 10 11 12 31 Week
Determine Exposure Period December 1, 2013 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 32
Exposure Period December 1, 2013 33
Formulate hypothesis December 1, 2013 Make a best guess to explain the observations The hypothesis should explain most cases 34
Test the Hypothesis December 1, 2013 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 35
Institute Control Measures December 1, 2013 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 36
Control Measures December 1, 2013 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 37
Healthcare-Associated Infections Control Measures December 1, 2013 Type of transmission suspected Suggested action Contact- Cross-transmission (transmission between individuals) Patient isolation and barrier precautions determined by infectious agent(s) Contact- Hand transmission Improvements 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 devices Foodborne agent Elimination of the at-risk food 38
Evaluate Efficacy of Control Measures December 1, 2013 Cases cease to occur or return to endemic level No change (re-evaluate cases) 39
Communicate and Write a Final Report December 1, 2013 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 40
Summary December 1, 2013 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 41
References December 1, 2013 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 42
Web Resource December 1, 2013 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/proto col/investigation.pdf 43
Quiz 1. Outbreak investigations are performed primarily to: a. Gather clinical information about a disease b. Find the source of infections c. Make sure patients are treated d. All of the above 2. Epidemic curves help determine if the problem is on-going. T/F 3. Control measures for healthcare-associated infections include all except: a. Patient isolation b. Use of disposables c. Hand hygiene d. Immunisation December 1, 2013 44
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/ December 1, 2013 45
