Outbreak Investigations - NURS 1113 Epidemiology 2024 PDF

NURS 1113: Epidemiology March 2024 M. Emanuel-Frith At the end of the session students will be able to:  Differentiate between the terms, outbreak and cluster  Explain the purpose of outbreak investigations  Describe the steps involved in an outbreak investigation  Identify key decisions in an o...

NURS 1113: Epidemiology March 2024 M. Emanuel-Frith At the end of the session students will be able to:  Differentiate between the terms, outbreak and cluster  Explain the purpose of outbreak investigations  Describe the steps involved in an outbreak investigation  Identify key decisions in an outbreak investigation 2 What is an outbreak?  Sudden occurrence of a disease (or more cases of a disease) than expected  In a relatively limited geographical area or among specific group of people  Over a particular period of time What is a cluster?  Accumulation of cases of a disease or health event in a specified area  Over a given time period  Without regard to whether number of cases exceeds expectation (expected number is often not known) (CDC, 2012 – Principles of Epidemiology) 3  Study of a disease cluster or epidemic in order to control or prevent further spread of the disease in the population 4  Regular, timely review of surveillance data Alert clinician(s) notifying health department of unusual pattern (clustering of cases) or cases Observations by infectious control nurse, lab personnel etc.  Members of affected group bringing attention to the problem (e.g. occupational settings) 5 Control and prevention of the problem – (most important reason) Research and training (opportunity to learn) Public health programme considerations Public relations, political or legal concerns 6  Fundamental reason for conducting an outbreak investigation 1. Control and prevention 2. Research and training 3. Public health program considerations 4. Public relations, political or legal concerns  Disease control efforts depend on several factors e.g. - Knowledge of the agent - Natural course of the outbreak - Usual transmission mechanism of the disease - Control measures that are available 7  Outbreaks provide opportunities to gain new knowledge  For new or rare diseases, provides 1. Control and prevention 2. Research and training 3. Public health programme considerations 4. Public relations, political or legal concerns opportunity to define its natural history and at-risk population For already established diseases, may provide additional knowledge by assessing the impact of control measures  Outbreak investigations improve skills in logical thinking, problem-solving, quantitative skills, epidemiologic knowhow, judgment and diplomacy 8  Outbreaks can be used to evaluate 1. Control and prevention 2. Research and training 3. Public health programme considerations 4. Public relations, political or legal concerns effectiveness of a programme towards improving future directions and strategies  Weaknesses in public health prevention and control programmes can be identified  Provides opportunity to change or strengthen programme efforts 9  Public, political or legal concerns 1. Control and prevention 2. Research and training 3. Public health programme considerations 4. Public relations, political or legal concerns may be the driving force behind the decision to conduct an investigation  Some outbreak investigations are required by law 10 In 2022, twelve women from Fleece Land community died from cervical cancer.  State 4 reasons that might justify an investigation Adapted from Principles of Epidemiology - CDC, 2012 11 Ten steps Several steps may be carried out simultaneously Circumstances of outbreak may require different order in steps – order of first three steps are highly adjustable 12 1. Prepare for field work & establish existence of outbreak 2. Verify diagnosis 3. Establish case definition 4. Perform descriptive epidemiology 8. Formulate conclusion 7. Analyse the data 6. Investigate the disease 5. Formulate hypothesis 9. Implement control & preventive measures 10. Disseminate findings 13 Prepare for field work Investigative team must be well prepared before leaving for the field Preparations fall into two broad categories:  Scientific and investigative issues  Management and operational issues 14 Establish Existence of Outbreak  Observed cases should be greater than expected  Consider other explanations e.g.  Changes made in case definition  Lab error  Inaccurate medical diagnosis  Over-reporting  Increased interest in disease by healthcare providers  Increase in population size 15 Verify diagnosis Detailed history  Compare clinical findings with current findings Review case history, lab tests and related investigations  Summarize findings to guide case definition 16 Establish case definition Simple, practical, objective (standard set of criteria) Should identify persons who have condition of interest May have classifications – e.g. possible, probable, confirmed 17 Example of an established case definition – meningococcal disease  Clinical criteria - illness with sudden onset of fever (>38.5°C rectal or >38.0°C axillary) and one or more of the following: neck stiffness, altered consciousness, other meningeal sign or petechial or puerperal rash  Lab criterion – positive cerebrospinal fluid (CSF) culture Case Classification Suspected Probable Someone who meets the A suspected case with clinical case definition cloudy CSF or linked to a confirmed case Confirmed A suspected or probable case with lab confirmation Source: PAHO. Case Definitions Meningococcal Disease. Epidemiological Bulletin 2002; 22(4):14–5 18 Perform descriptive epidemiology  Identify infected persons and for each suspected case, determine clinical and / or biological criteria  Person (Who are affected? Who are at risk?)  Place (Where are they affected? Spot map can be helpful sometimes)  Time (When are they affected?) – epidemiology curve helps to identify incubation period, period of exposure, pattern of spread of the disease, magnitude of outbreak, natural course of outbreak 19 Perform descriptive epidemiology Time 20 Formulate hypothesis Should be precise (utilizes information from descriptive epidemiology) Investigate the disease Conduct detailed investigation Evaluate hypothesis (analytic epidemiology – case control or retrospective cohort study) 21 You are called to help investigate a cluster of 17 persons who developed brain cancer in an area over the past couple of years. Most, perhaps all, used cell phones. Which study design would you choose to investigate a possible association between cell phone use and brain cancer? CDC, 2012 22 Investigators conducted a case-control study of histoplasmosis among industrial plant workers in Nebraska.41 The following table shows the number of case-patients and controls who worked in Building X, near a recently excavated site Cases Bldg X 15 Other bldg. Total 1. Complete the table Controls Total 23 23 22 53 2. What is the appropriate measure of association? 3. 2. Calculate this measure. Adapted - CDC, 2012 23 Analyse the data Relative risk or odds ratio useful measurements Formulate conclusion Based on all pertinent evidence (obtained from all team members / sources) 24 Implement control and preventive measures As soon as link in disease transmission is identified Continue surveillance Disseminate findings Report should be clear and comprehensive to nontechnical decision makers Include feasible short-term and long-term recommendations 25 http://www.youtube.com/watch?v=cQ9kVm4GU68 26  You are a young epidemiologist and have been called to investigate a disease outbreak at a hotel. Six out of every ten visitors have fallen ill with a serious ailment of unknown origin.  You have been mandated to trace the outbreak origin so that control measures can be implemented.  Use the basic methods of field epidemiology to solve this medical mystery (See website below) https://www.pbs.org/wgbh/nova/typhoid/detective.html 27  Class participation 28  A systematic approach ensures that important steps are not missed during the investigation Communicate findings Implement control and preventive measures Formulate a conclusion Analyse the data Investigate the disease Formulate hypothesis Perform descriptive epidemiology Formulate working case definition Verify diagnosis 29  Matching Exercises  Chapter 10: Field Epidemiology Question 1 of 2  http://publichealth.jbpub.com/merrill/epidemiologyworkbook/matching.aspx?ch apter=10 30