methods of epidemiological investigation

Methods of Epidemiological investigation

Epidemiology is the scientific process

applied to the control of infections in the healthcare setting.

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’

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)

Epidemiology and Clinical Medicine

Relationship between

Studies/Assessments

Prevention

Evaluation

Planning

Diagnosis

Treatment

Cure

Care

Examples of Epidemiological Studies

• Link between smoking and lung cancer

Doll & Hill, 1964

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

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

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

Key components of epidemiological studies

StudyPopulation/

Sample

Exposure to a study factor

Outcome

Unexposed

Exposed

Target Population


• 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


• 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.

• 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


• 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.

•How is Hospital Epidemiology different from Healthcare Epidemiology?

•Healthcare Epidemiology extends the practice into the outpatient areas.

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

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

• Additional morbidity• Prolonged hospitalization• Long-term physical,

developmental and neurological sequelae

• Increased cost of hospitalization• Death

Consequences of Nosocomial Infections

What is healthcare epidemiology?

The fundamental roles of healthcare epidemiology are to:

– Identify risks

– Understand risks

– Eliminate or minimize risks

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?

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

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

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

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

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

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

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)

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

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

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

Transmission-based Precautions

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

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

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

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

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)

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

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

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!!

The surveillance loop

Event

Action

Data

Information

Health care system

Surveillance centre

Reporting

Feedback, recommendations

An

alysis, in

terpretation

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

Who

• All hospitals?

• All departments?

• All specialties?

• Other health institutions?

Surveillance of one or more types of NCI

Urinary tract infections

Lower respiratory tract infections

Surgical site infections

Bloodstream infections

Conjunctivitis

Others…

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)

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

When?

• During hospital stay?– Frequency of data collection

• After discharge?– When and how?

How?

• Two main surveillance methods – incidence– prevalence

• Variations within these methods

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?

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

methods of epidemiological investigation

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