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Methods of Epidemiological investigation
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Epidemiology is the scientific process
applied to the control of infections in the healthcare setting.
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Origin of the term ‘epidemiology’
• epi - ‘on, upon, at, by, near, over, on top of, against, among’
• demos - ‘common people or citizenry’• ology - ‘the study of’• epidemiology =‘Study of disease among
the population’
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Epidemiology is about Populations
• Groups of people not individuals• It answers population questions
– aetiology of disease – prevention of disease– Extent/distribution of disease (allocation of
effort & resources in health facilities and communities)
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Epidemiology and Clinical Medicine
Relationship between
Studies/Assessments
Prevention
Evaluation
Planning
Diagnosis
Treatment
Cure
Care
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Examples of Epidemiological Studies
• Link between smoking and lung cancer
Doll & Hill, 1964
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Examples of Epidemiological StudiesWater fluoridation:
•Communities that had low natural water fluoride levels had high levels of dental caries
•Communities that had high natural water fluoride levels had low levels of dental caries
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Uses of Epidemiology(Gordis, 2000)
• Identifies aetiology or causes of disease including the risk factors for the disease.
• Determine the extent of the disease in the community
• Examines natural history of disease and prognosis of disease
• Investigates and controls disease outbreaks
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Uses of Epidemiology(Gordis, 2000)
• Describes and monitors the population health and the patterns of disease
• Evaluates new preventive and therapeutic interventions and modes of health care delivery
• Provides information to inform public policy decisions
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Key components of epidemiological studies
StudyPopulation/
Sample
Exposure to a study factor
Outcome
Unexposed
Exposed
Target Population
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Key components of epidemiological studies
• Target population is the population a researcher wants to make generalizations about
• Study population is the group a researcher wishes to study (sometimes the same as the target population)
• Study sample is a group of subjects chosen for study to represent the study population
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Key components of epidemiological studies
• Study factor – is a element that is being investigated to see if it is
a determinant of a particular health problem – or if it reduces the impact of a particular health
problem. – Study factors can include
• risk factors for a health problem,• interventions (therapeutic or
preventative) to ameliorate a health condition,
• diagnostic tests or techniques and • environmental exposures.
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• Exposure is contact with or possessing a particular study factor
• Exposed group is a group whose members have had contact with or possess a study factor
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Key components of epidemiological studies
• Unexposed group is a group that has not had contact with a cause of, or possess a characteristic that is a determinant of, a particular health problem.
• Outcome is any or all of the possible results that may stem from an exposure or study factor.
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•How is Hospital Epidemiology different from Healthcare Epidemiology?
•Healthcare Epidemiology extends the practice into the outpatient areas.
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History of infection control and hospital epidemiology in the USA
• Pre 1800: Early efforts at wound prophylaxis• 1800-1940: Nightingale, Semmelweis, Lister, Pasteur• 1940-1960: Antibiotic era begins, Staph. aureus
nursery outbreaks, hygiene focus• 1960-1970’s: Documenting need for infection control
programs, surveillance begins• 1980’s: focus on patient care practices, intensive
care units, resistant organisms, HIV • 1990’s: Hospital Epidemiology = Infection control,
quality improvement and economics• 2000’s: ??Healthcare system epidemiology
modified from McGowan, SHEA/CDC/AHA training course
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Why do we need infection control??
Hospitals and clinics are complex institutions where patients go to have their health problems diagnosed and treated
But, hospitals, clinics, and medical/surgical interventions introduce risks that may harm a patient’s health
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• Additional morbidity• Prolonged hospitalization• Long-term physical,
developmental and neurological sequelae
• Increased cost of hospitalization• Death
Consequences of Nosocomial Infections
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What is healthcare epidemiology?
The fundamental roles of healthcare epidemiology are to:
– Identify risks
– Understand risks
– Eliminate or minimize risks
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What is the role of healthcare
epidemiology?Identify risks to patient’s health
• Find nosocomial infections– surveillance
• Identify and study risk factors for nosocomial infections– understand epidemiologic principles and
methods– understand nosocomial pathogens– what is it about healthcare institutions
that increases risk?
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What is the role of healthcare
epidemiology?Eliminate or minimize risks to a patient’s
health
• organize care to minimize risk– eliminate risk factors– work around risk factors– develop improved policies and procedures
• educate physicians and nurses regarding risks
• study risk factors to learn more about them and how to eliminate them
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Responsibilities of the Infection Control Program
• Surveillance of nosocomial infections
• Outbreak investigation• Develop written policies
for isolation of patients• Develop written policies
to reduce risk from patient care practices
• Cooperation with occupational health
• Education of hospital staff on infection control
• Ongoing review of all aseptic, isolation and sanitation techniques
• Eliminate wasteful or unnecessary practices
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Areas of interest to a healthcare epidemiologist
• Surveillance for nosocomial infection
• Patterns of transmission of nosocomial infections
• Outbreak investigation
• Isolation precautions
• Evaluation of exposures
• Employee health• Disinfection and
sterilization• Hospital
engineering and environment– water supply– air filtration
• Reviewing policies and procedures for patient care
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Organizing for Infection Control
• Requires cooperation, understanding and support of hospital administration and medical/surgical/nursing leadership
• There is no simple formula:– Every facility is different– Every facility’s problems are different– Every facility’s personnel are different
• The facility must develop its own unique program
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Organizing for Infection Control
• Main elements– Establish policies and regulations to reduce
risks• Develop with clinicians (physicians and nurses)
– Develop and maintain a program of continuing education for hospital personnel
– Use scientific (epidemiologic) methods to study problems and test hypotheses
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Disease Transmission
Leave original host
Survive in transit
Be delivered to a susceptible host
Reach a susceptible part of the host
Escape host defenses
Multiply and cause tissue damage
To cause disease, a pathogenic organism must:
Disease
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Routes of Transmission• Contact: Infections spread by direct or indirect contact
with patients or the patient-care environment (e.g., shigellosis, MRSA, C. difficile)
• Droplet: Infections spread by large droplets generated by coughs, sneezes, etc. (e.g., Neisseria meningitidis, pertussis, influenza)
• Airborne (droplet nuclei): Infections spread by particles that remain infectious while suspended in the air (TB, measles, varicella, variola)
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Precautions to Prevent Transmission of Infectious Agents
• Standard PrecautionsApply to ALL patients
• Transmission-based PrecautionsUsed in addition to Standard Precautions
• Contact• Droplet• Airborne
http://www.cdc.gov/ncidod/dhqp/pdf/guidelines/Isolation2007.pdf
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Standard Precautions
• Hand hygiene• Respiratory hygiene and cough etiquette• Personal protective equipment (PPE)
Based on risk assessment to avoid contact with blood, body fluids, excretions, secretions
• Safe injection practices• Environmental control• Patient placement
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PPE for Standard Precautions
• Gloves – when touching blood, body fluids, secretions, excretions, mucous membranes, non-intact skin, contaminated items
• Gowns – during procedures or patient-care activities when anticipating contact with blood, body fluids, secretions, excretions
• Mask, eye protection (goggles or face shield) – during procedures or patient care activities likely to generate splashes or sprays
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Transmission-based Precautions
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Contact Precautions
• Patient placement– Single room or cohort with patients with same infection– If neither is possible, ensure patients are separated by at
least 3 ft (1 m)*Change PPE and perform hand hygiene between
patient contacts regardless of whether one or both are on contact precautions
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Contact Precautions
• Environmental measures/patient care equipment– Clean patient room daily using a hospital disinfectant, with attention
to frequently touched surfaces (bed rails, bedside tables, lavatory surfaces, blood pressure cuff, equipment surfaces).
– Use dedicated equipment if possible (e.g., stethoscopes, bp cuffs)
PPE Gown and gloves
Don upon entry to room Remove and discard before leaving the roomPerform hand hygiene after removal
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Droplet Precautions• Patient placement
– Single room or cohort with patients with same infection– If neither is possible, ensure patients are separated by at least
3 ft (1 meter)– Surgical mask on patient when outside of patient room– Negative pressure or airborne isolation rooms not required
PPE • surgical mask
• Don upon entry into room • Eye protection (goggles or face shield) if needed according to standard precautions
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Airborne Isolation
Airborne infection isolation room (AIIR)*
Monitored negative air pressure in relation to corridor
6-12 air exchanges/hour
Air exhausted outside away from people or recirculated by
HEPA filter
Surgical mask on patient when not in AIIR (limit movement)
PPE – filtering facepiece respirator
For all personnel inside negative pressure room
* Natural ventilation alone or combined with mechanical ventilation may be a practical alternative in some settings.http://www.who.int/csr/resources/publications/AI_Inf_Control_Guide_10May2007.pdf
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TYPES OF NOSOCOMIAL
INFECTION BY SITE 1. Urinary tract infections (UTI)
2. Surgical wound infections (SWI)
3. Lower respiratory infections (LRI)
4. Blood stream infections (BSI)
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EPIDEMIOLOGICAL INTERACTIONIntrinsic host susceptibility Age, Poor nutritional status, Co morbidity, severity of underlying disease
Agent factors varieties of organisms
Institutional and human
Reservoirs & their virulence
Environmental factors hospital location, diagn procedures, immunosuppressive, chemotherapy, antibiotics, med & surgical devices, exposure to infected patients or health workers, asymptomatic carriers
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MODES OF TRANSMISSION
A) BY CONTACT
1) Direct - between Patients and between
patient care personnel
2) Indirect - contaminated inanimate objects
in environment (Endoscopes etc)
3) Droplet infections by large aerosols
B) THRO COMMON VEHICE like Food, Blood & blood products, Diagnostic reagents, Medications
C) AIRBORNE e.g. legionellosis, aspergillosis
D) VECTORBORNE – by flies
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Why surveillance?
• NCI cause of morbidity and mortality
• One third may be preventable
• Surveillance = key factor – an infection control measure– overview of the burden and distribution of NCI– allocate preventive resources
• Surveillance is cost-efficient!!
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The surveillance loop
Event
Action
Data
Information
Health care system
Surveillance centre
Reporting
Feedback, recommendations
An
alysis, in
terpretation
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Objectives
• Reducing infection rates• Establishing endemic baseline rates• Identifying outbreaks• Identifying risk factors• Persuading medical personnel• Evaluate control measures• Satisfying regulators• Document quality of care• Compare hospitals’ NCI rates
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Who
• All hospitals?
• All departments?
• All specialties?
• Other health institutions?
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Surveillance of one or more types of NCI
Urinary tract infections
Lower respiratory tract infections
Surgical site infections
Bloodstream infections
Conjunctivitis
Others…
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Targeted surveillance
• Special patient population(surgical, medical, paediatric, intensive)
• Diagnostic and therapeutic procedures(endoscope, haemodialysis, catheterization,
blood transfusion)
• Specific pathogens(staphylococcus aureus, MRSA,
clostridium difficile, norovirus)
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Variables
• Administrative data– Id, address, dates of admission, discharge..
• Patient related factors:– Age, sex, severity of underlying disease
• Procedures– Surgery– Devices (e.g. catheters)
• Treatment, diagnosis– Use of antibiotics
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When?
• During hospital stay?– Frequency of data collection
• After discharge?– When and how?
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How?
• Two main surveillance methods – incidence– prevalence
• Variations within these methods
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Methodological issues • Definitions NCI
– Cut off 48 or 72 hours?– Criterias from Centers for Disease Control and Prevention
(hospital)– McGeer (long-term care facilities)Risk variables
• Case finding– Active or passive– By whom?– After discharge?– Prospective or retrospective?
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SURVEILLANCE
Important means of monitoring HAI Early detection of trends outbreaks 1. Laboratory Based Microbiology Laboratory lists +ve organisms ICN reviews ‘Alert organisms’ reported 2. Ward Based Ward staff monitor patientsICN reviews ICN visits wards
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