Disease Outbreaks Year 2 25/09/2024 (RCSI) PDF

DISEASE OUTBREAKS YEAR 2 25/09/2024 Lecturer: Dr. Lois O’Connor  Acknowledgements Some content in this slide set has been taken, with permission, from materials developed by the European Centre for Disease Prevention and Control Fellowship Programme in Intervention Epidemiology...

DISEASE OUTBREAKS YEAR 2 25/09/2024 Lecturer: Dr. Lois O’Connor  Acknowledgements Some content in this slide set has been taken, with permission, from materials developed by the European Centre for Disease Prevention and Control Fellowship Programme in Intervention Epidemiology Training (EPIET) Dr Paul McKeown, Dr Patricia Garvey : HSE- Health Protection Surveillance Centre  Learning outcomes  Summarise why outbreaks are important causes of illness and death  Recognise the mechanisms of transmission of various pathogens and their management strategies  List and apply the steps in the management of an outbreak  Develop a case definition  Use an epidemiological study to determine the source of an outbreak  What is an outbreak? Occurrence of more cases than expected of an illness – During a particular time period (TIME) – In a particular place (PLACE) – Among a specific group of people (PERSON)  Why investigate outbreaks? Important cause of human illness and deaths Can be controlled (control the outbreak and minimise human harm) Understand what happened and why Prevent future outbreaks – improve our knowledge Improve surveillance and outbreak detection Training  Importance of Outbreaks Ireland 2019 646 outbreaks of infectious diseases 5852 outbreak-associated cases of illness Gastrointestinal/respiratory pathogens mainly COVID-19 Outbreaks 27,610 COVID-19 outbreaks since March 2020 (as of May 18th 2024) s://www.hpsc.ie/a-z/outbreaks/surveillancereports/ s://www.hpsc.ie/a-z/respiratory/coronavirus/novelcoronavirus/surveillance/covid-19outbreaksclustersinireland/ Outbreaks Steps of an outbreak investigation 1. Establish the existence of a real outbreak findings Communicate 2. Confirm the diagnosis measures Control 3. Define a case 4. Search for cases 5. Generate hypotheses using descriptive findings 6. Test hypotheses using analytical epidemiology 7. Conduct additional investigations 8. Draw conclusions 9. Communicate findings 10. Execute control and prevention measures Steps of an outbreak investigation 1. Establish the existence of a real outbreak findings Communicate 2. Confirm the diagnosis measures Control 3. Define a case 4. Search for cases 5. Generate hypotheses using descriptive findings 6. Test hypotheses using analytical epidemiology 7. Conduct additional investigations 8. Draw conclusions 9. Communicate findings 10. Execute control and prevention measures  1. Detection 1. Systematic surveillance Disease notifications of notifiable infectious diseases (laboratory or clinical) 2. Detection of additional cases during investigation of a sporadic case 3. An alert clinician 4. General public 5. Media 10 Could it be a pseudo-outbreak? Artefact in the numerator: – Increased awareness – Change in surveillance practices – Reporting of prevalent cases as incident cases (e.g., hepatitis C, chronic hepatitis B) – Laboratory error Variation of the denominator: – Rapidly changing population denominators Hospital patients, migrants, refugees, mass gathering  Outbreak Control Team (OCT) OCT members Responsibilities o Public Health Physicians o Coordinate all outbreak management activities o Clinical staff o Liaison o Environmental Health Officers o Media o Clinical Microbiologist o Maintain a record of the o Logisticians investigation o Food Safety Authority o Produce reports o Reference Laboratories Steps of an outbreak investigation 1. Establish the existence of a real outbreak findings Communicate 2. Confirm the diagnosis measures Control 3. Define a case 4. Search for cases 5. Generate hypotheses using descriptive findings 6. Test hypotheses using analytical epidemiology 7. Conduct additional investigations 8. Draw conclusions 9. Communicate findings 10. Execute control and prevention measures  2. Confirm the diagnosis A two-stage process 1. Clarify the syndrome and identify diagnoses – Communicate with clinicians, specialists – Examine the frequency of symptoms among cases – Which age groups affected? 2. Confirm diagnosis with laboratory tests – Discuss best tests to use with laboratory and Steps of an outbreak investigation 1. Establish the existence of a real outbreak findings Communicate 2. Confirm the diagnosis measures Control 3. Define a case 4. Search for cases 5. Generate hypotheses using descriptive findings 6. Test hypotheses using analytical epidemiology 7. Conduct additional investigations 8. Draw conclusions 9. Communicate findings 10. Execute control and prevention measures  3. Define a case = clinical/laboratory criteria plus restrictions which characterise the outbreak (time, place, person) time (e.g. persons with onset of illness from x date) place (e.g. residents of a region, attendees at an event) person (clinical/lab criteria and sometimes restrict by age, sex, ethnicity etc) Apply to everyone under investigation Don’t be too restrictive or you won’t find all the cases The case definition must not include the exposure or risk factor suspected to be the source/cause of the outbreak  Example outbreak case definition Scenario – unwell wedding guests A person who attended the wedding at hotel X on 25 June 2010, who reported an illness with diarrhoea or vomiting and with an onset of illness between 26 June 2010 and 5 July 2010  Exercise - develop a case definition Since mid June 2017, 37 confirmed cases of hepatitis A have been notified to Public Health England across England and Northern Ireland. 28 of the cases identified as men who have sex with men. What is your working case definition? Exercise - develop a case definition A person with laboratory confirmed hepatitis A with onset of symptoms since June 2017 in England and Northern Ireland The men who have sex with men exposure characteristic is not included but is likely to be a hypothesis that is further examined in an epidemiological study Steps of an outbreak investigation 1. Establish the existence of a real outbreak findings Communicate 2. Confirm the diagnosis measures Control 3. Define a case 4. Search for cases 5. Generate hypotheses using descriptive findings 6. Test hypotheses using analytical epidemiology 7. Conduct additional investigations 8. Draw conclusions 9. Communicate findings 10. Execute control and prevention measures  4. Search for cases “Casting your net” Start with the case definition and population at risk Aim for uniform strategy to search for cases – Passive (usual) surveillance – Active surveillance Alert clinicians, microbiologists, Known members of population at risk Direct search in medical records Snowball – Community/public search Door to door / media alert  Steps of an outbreak investigation 1. Establish the existence of a real outbreak findings Communicate 2. Confirm the diagnosis measures Control 3. Define a case 4. Search for cases 5. Generate hypotheses using descriptive findings 6. Test hypotheses using analytical epidemiology 7. Conduct additional investigations 8. Draw conclusions 9. Communicate findings 10. Execute control and prevention measures  5. Generate hypotheses using descriptive findings Describe the cases you have identified Descriptive epidemiology: Time (epidemic curve) number of cases, date of onset of symptoms Place (map) location of cases Person (case characteristics and exposures)  Trawling questionnaires to generate hypotheses Open ended questionnaires for cases Look for common (high frequency) exposures – Event they participated in? – Place they visited? – Behaviour they have in common?  Person Characteristics age, sex, race/ethnicity, religion, medical history Possible exposures diet, occupation, leisure activities, social behaviours, use of medications, drugs, alcohol, smoking date and location of exposure  Place Provides geographic extent of problem May demonstrate clusters or patterns that provide important etiologic clues Spot maps - illustrate where cases live, work or may have been exposed p://en.wikipedia.org/wiki/1854_Broad_Street_cholera_outbreak  Map of measles cases in outbreak Dublin 2011 Fitzpatrick G et al. Use of a geographic information system to map cases of measles in real-time during an  Time - Epidemic curves mic curves show the size of the epidemic over time in a simple, easily understoo Advantages: distinguish epidemic from endemic Examples of Epidemic Curves disease 30 add events onto the graph (e.g. war, 25 Point source earthquake) Continuing source 20 pattern of spread (e.g. point source vs No ill 15 10 continuing) identify stage of epidemic —upswing, 5 0 down slope, post Mon Tue Wed Thu Fri Sat Sun Mon Tue Wed Thu Onset day Fri Sat Sun Mon Tue evaluation (e.g. are control measures working?) outliers (cases outside the curve) may provide clues estimate probable time of exposure (if CDC. https://www.cdc.gov/ophss/csels/dsepd/ss1978/lesson6/section2.html#step6  Time - Epidemic curves Outbreak of Salmonella enteritidis Gastroenteritis — Maryland, 2003 https://www.cdc.gov/OPHSS/CSELS/DSEPD/SS1978/Lesson6/Section2.html#_ref32 Source: Castel AD, Blythe D, Edwards L, Totaro J, Shah D, Moore M. A large outbreak of Salmonella Enteritidis infections associated with crabcakes at a church fundraiser–Maryland, 2003. Presented at 53rd Annual Epidemic Intelligence Service Conference, April 19–23, 2004, Atlanta.  Epidemic curve hepatitis A outbreak 2013 Fitzgerald M et al on behalf of the Hepatitis A Outbreak Control Team Collective. Outbreak of hepatitis A infection associated with the consumption of frozen berries, Ireland, 2013 - linked to an international outbreak. Euro Surveill. 2014;19(43) Steps of an outbreak investigation 1. Establish the existence of a real outbreak findings Communicate 2. Confirm the diagnosis measures Control 3. Define a case 4. Search for cases 5. Generate hypotheses using descriptive findings 6. Test hypotheses using analytical epidemiology 7. Conduct additional investigations 8. Draw conclusions 9. Communicate findings 10. Execute control and prevention measures  6. Test hypotheses using analytical epidemiology Use an epidemiological study to demonstrate association between illness and specific demographic/exposure (i.e. age groups, foods eaten, locations attended) 1. Cohort - when the affected population is known (wedding, flight, nursing home) and a complete list is available ‒ contact each person on list ‒ assess disease status and exposures ‒ use only when population is well defined and can be followed up over time 2. Case control - when the affected population is not well defined or due to urgency/resource constraints the whole population cannot be followed up ‒ contact those with disease (cases) plus a comparison group without disease (controls) ‒ assess exposures Steps of an outbreak investigation 1. Establish the existence of a real outbreak findings Communicate 2. Confirm the diagnosis measures Control 3. Define a case 4. Search for cases 5. Generate hypotheses using descriptive findings 6. Test hypotheses using analytical epidemiology 7. Conduct additional investigations 8. Draw conclusions 9. Communicate findings 10. Execute control and prevention measures  7. Conduct additional investigations Laboratory studies – Microbiological typing Identical isolates among cases Identical isolates in source and cases Other investigations – Environmental (e.g., test water, vector studies, visit the kitchen) – Anthropological (e.g., understand a practice at risk) – Veterinarian (e.g., test animals in zoonotic disease outbreaks) Steps of an outbreak investigation 1. Establish the existence of a real outbreak findings Communicate 2. Confirm the diagnosis measures Control 3. Define a case 4. Search for cases 5. Generate hypotheses using descriptive findings 6. Test hypotheses using analytical epidemiology 7. Conduct additional investigations 8. Draw conclusions 9. Communicate findings 10. Execute control and prevention measures  8. Draw conclusions Interpretation of all the collected outbreak information incl. descriptive and analytical epidemiology Is the suspected exposure associated with illness? – What is the strength of association? – Is there a statistical significance? – Causality? Is there a dose response relationship? – Higher exposure, stronger association Does the source/vehicle identified explain most cases? – Are most of the cases exposed? Steps of an outbreak investigation 1. Establish the existence of a real outbreak findings Communicate 2. Confirm the diagnosis measures Control 3. Define a case 4. Search for cases 5. Generate hypotheses using descriptive findings 6. Test hypotheses using analytical epidemiology 7. Conduct additional investigations 8. Draw conclusions 9. Communicate findings 10. Execute control and prevention measures  9. Communicate findings Aim: prevent recurrence 1.Write report, publish paper, website update, produce guidelines/protocols, change legislature 2.Make recommendations 3.Lessons learned from outbreak investigation/management Steps of an outbreak investigation 1. Establish the existence of a real outbreak findings Communicate 2. Confirm the diagnosis measures Control 3. Define a case 4. Search for cases 5. Generate hypotheses using descriptive findings 6. Test hypotheses using analytical epidemiology 7. Conduct additional investigations 8. Draw conclusions 9. Communicate findings 10. Execute control and prevention measures  10. Control Measures What should be done? 1.Agent: remove source of infection Treat (or isolate) cases, destroy/stop sale/remove/disinfect 2.Host: protect those at risk Hygiene, chemoprophylaxis, immunisation, protective clothing, insect repellent 3.Environment: Interrupt transmission (prevent spread) Environmental cleaning, hygiene, isolation, spraying 4.Surveillance: review acceptability and effectiveness of control measures 5.Communication strategy  Routes of food contamination Contamination of raw food – Farming practice/abattoir practice/zoonotic problems – Pasteurisation failure – Consumption of raw food Contamination during food preparation – Infected food handler – Environmental contamination – Preparation of food too far in advance – Cross contamination (from raw or processed ingredients) Contamination after food preparation – Infected food handler – Inadequate/incorrect storage, cooling or reheating – Environmental contamination – Cross contamination from raw food – Undercooking food Food can become contaminated at any stage in the “farm to fork” pathway  Identifying the cause of food contamination Inspection/examination of: 1. Food premises – Environmental Health Service – Staff symptoms – Observation of food preparation practices (storage of raw/cooked foods) – Records of staff sickness, temperature charts (fridges/freezers/ovens), cleaning 2. Commercial food preparation premises – Environmental Health Service – Records (temperature charts, quality control, staff sickness) and checking of instrument calibration (thermometer) – HACCP (hazard analysis of critical control points) and inspection of production line – Inspection of supplier records 3. Food chain – Food Safety Authority of Ireland – Manages risks in the food chain and respond effectively to any national or international food incident or crisis 4. Farms – Department of Agriculture – Records (pasteurisation temperature charts, veterinary records, staff sickness) – Observation of animal husbandry and crop management Gastrointestinal disease outbreaks Most outbreaks are gastrointestinal = 70-90% of outbreaks in developed countries (Ireland gastrointestinal =390/558 outbreaks in 2017) Viruses are responsible for the largest number of cases (e.g. norovirus, rotavirus) Minority are foodborne (3% in Ireland) or waterborne (3%)  Salmonellosis at a fish restaurant Fish restaurant 600 diners in one day - majority during the day 136 became ill Salmonella enteritidis Eggs were contaminated Used to make mayonnaise The restaurant was famous for its fish cakes and mayonnaise Mayonnaise was contained in bowl by an Aga range Eggs and other ingredients were added through out the day Therefore the Salmonella load increased over the day dose response  Analytical epidemiological study To demonstrate association between illness and specific exposure. In a likely food-borne outbreak – demonstrate association between illness and a specific food. 1. Cohort - when the affected population is known Measure of association is Relative Risk 2. Case control - when the affected population is not well defined or due to urgency/resource constraints the whole population cannot be followed up Measure of association is Odds Ratio  Relative risk The relative risk in a cohort study is the measure of association used to quantify the which risk factor/exposure is more likely to be associated with illness In a suspected food-borne outbreak: Which food is more likely associated with illness?  First, attack rate There can be many…. Attack rate: the proportion of people within the group who became ill Age-specific attack rate: the proportion within an age group who became ill Sex-specific attack rate: the proportion of males or females who became ill Food specific attack rate:  Attack rate Example 100 people at a wedding Illness (contaminated food) - norovirus 45 get sick, 55 remain well AR = 45/100 = 45%  Relative risk You can easily calculate the relative risk (RR) using the attack rate (AR) Relative risk = AR in those exposed to risk factor ÷ AR in those not exposed to risk factor OR Relative risk (for a particular food) = AR in those who ate the particular food ÷ AR in those who did not eat the particular food  Food specific AR example Funeral party, 100 people Sandwiches include canned tuna, canned crab, salmon, turkey, salad What is the attack 13 people develop botulism rate? Botulism 10 people with botulism ate tuna Yes No Total Tuna Yes 10 30 sandwiches No 3 30 people ate tuna Total 13 100 sandwiches in total  Food specific AR example Funeral party, 100 people Sandwiches include canned tuna, canned crab, salmon, turkey, salad 13 people develop botulism Botulism Yes No Total 10 people with botulism ate tuna Tuna Yes 10 20 30 sandwiches No 3 67 70 30 people ate tuna Total 13 87 100 sandwiches in total  Food specific RR example Relative risk = AR in those who ate particular food/ AR in those who did not eat particular food Botulism ARtuna = 10/30 or 33% Yes No ARno tuna = 3/70 or 4.3% Tuna Yes 10 20 30 RRtuna= 10/30 ÷ 3/70 = 10/30 x 70/3 No 3 67 70 = 7.7 13 87 100  You were nearly eight times as likely to develop botulism if you ate a tuna sandwich than if you did not eat a tuna sandwich  TIME FOR QUESTIONS  “HOMEWORK”  THANK YOU  E-mail: [email protected] 53