PPN 302 Class 11: Communicable diseases, control & management, epidemiology

Host defined

• The organism harbouring the disease (the “who” of the triangle) 

Agent defined

• The microbe that causes the disease (the “what” of the triangle)

Environment defined 

• The external factors that cause or allow disease transmission (the “where” of the triangle) 

Outbreak defined

• The occurrence of cases of disease in excess of what would normally be expected in a defined community, geographical area or season 

• May occur in a restricted geographical area, or may extend over several countries. May last for a few days or weeks, or for several years. (WHO, 2014)

Epidemic defined 

• The occurrence of more cases of disease than expected in a given area or among a specific group of people over a particular period of time. Similar to an outbreak, but an epidemic is generally more widespread in the population and often has more serious connotations.

Endemic defined

• An infectious disease that occurs frequently in particular local e.g malaria, is endemic to some parts of Africa 

Pandemic defined 

• When a disease spreads rapidly across the globe, essentially a global epidemic 

Syndemic defined 

• Synergistic interaction of 2 or more coexisting diseases and the resultant excess in the burden of disease

Prevalence defined 

• Number of cases (new and preexisting) 

Mortality rate defined 

• Number of deaths from a specific cause in a given pop in a time period 

Pathognicity defined

• The agent’s capacity to cause disease in an infected host 

Virulence defined 

• The ability of the agent to produce serious illness 

Reservoir defined 

• Habitat or medium in which an agent lives and/or multiplies

  •  Can be living or inanimate

Communicable diseases defined by Heyman, 2015

• Illness caused by a specific infectious agent or its toxic products that arises through transmission of that agent, or its products from an infected person, animal or inanimate source to a susceptible host; either directly or indirectly through an intermediate plant or animal host, vector or the inanimate environment

Communicable diseases defined 

• Worldwide, infectious diseases create a burden on individuals, communities & the health care system

  • exact a greater toll on infants, young children and the elderly

  • disproportionately affect disadvantaged populations in developing & developed countries.”

19th century (Historical perspective on communicable diseases)

• Problems related to lack of understanding of disease transmission 

Mid 20th century (Historical perspective on communicable diseases)

• Epidemics of infectious diseases are mostly limited to developing countries 

• Still primarily a public health issue 

• Diarrhea, venereal diseases, leprosy, TB, malaria & other parasitic diseases

21st century (Historical perspective on communicable diseases)

• Globalization creates conditions for wide geographical range for disease transmission

Shifts with the new science of epidemiology (Historical perspective on communicable diseases)

• Understanding of etiology & modeof  transmission → measures for control

• antimicrobial/ antibiotic resistance

• New toxins, strains of older illnesses

Direct transmission (Modes of transmission) 

• of pathogen through physical contact between an infected person and a susceptible person (sexual intercourse, Skin to skin, Direct Contact, Ingestion, Aerosol) 

Examples of direct transmission

• Person to person; skin to skin, contact with oral secretions; sexual intercourse; contact with body lesions; transplacental.

• Iinfctd vector to host

• Diseases spread exclusively by direct contact are unable to survive for significant periods of time away from a host

Indirect transmission (modes of transmission) 

• occurs from a contaminated surfaces or objects. In this case inanimate object serves as the infectious agent. Occurs when living organisms transfer disease between animals (mosquitoes, flies, mites, fleas, ticks, rodents)

Examples of indirect transmission

• Contaminated inanimate objects

• Surgical equipment

• Toys, food 

• Airborne & dust: TB, chickenpox, measles 

• Fecal matter

 Vector: indirect transmission 

• Animals capable of transmitting disease

• E.g.: flies, mites, fleas, ticks, rats, and dogs. Mosquito is the

• most common form

• Transmission can occur through biting, feces or on the surface of it, that then touches other surfaces are mobile; therefore, increase the reach of an illness

Largest droplets (airborne & dust indirect transmission)

• Fall to the ground in seconds; may persist in dust, but not an important cause of infection 

Medium-sized droplets (airborne & dust indirect transmission)

• Trapped & cleared in the upper airways

Smallest droplets (airborne & dust indirect transmission)

• (<25mm) evaporate, leaving “droplet nuclei” of bacilli that can reach alveoli (e.g TB)

Immunity defined 

• Resistance on the part of the host to a specific infectious agent 

Active immunity defined 

• The body produces its own antibodies following contact with antigen 

Examples of active immunity

• infection 

• Immunization

Passive immunity defined 

• Person receives pre-formed antibodies. Frequently shorter duration of immunity 

Examples of passive immunity

• Antibody transfer 

• Maternal e.g breast feeding 

Herd immunity 

• The resistance of a population or group to the invasion and spread of an infectious agent

• Based on the level of resistance in a population.

  • A high proportion of the population cannot get the disease because of previous vaccination or infection

• Barrier to direct transmission due to lack of susceptible individuals in the population

Epidemiology defined

•  The study of the distribution and determinants of health  and illness (health-related states and events, not just diseases), and the application of knowledge to control the health problem in specific population

Factors of epidemiology 

• The frequency and patterns of disease occurrence in human populations 

• The factors that influence these patterns

• Involves applying the knowledge gained by the studies to community-based practice

• The measurement of disease outcomes in relation to a population at risk

Importance of epidemiology 

• Helps determine the etiology, risk factors or risk conditions of diseases

• Helps in the study of injuries and injury prevention

• Includes notions of social epidemiology– explicit attention to role of SDH in risk factors/conditions for disease and injury

• Public health practitioners use epidemiological data to determine the need for programs and services.

Demography 

• Central to epidemiology 

• The study of populations 

  • Looks at things including: size and density, fertility, mortality, growth, age distribution, migration, and vital statistics 

Social epidemiology

• incorporates the interaction of more quantifiable characteristics (e.g. gender, age, ethnicity) with social and economic conditions.

Epidemiological variables that influence risk/ susceptibility

• susceptibility 

• person

• time

• place

Susceptibility (Epidemiological variables that influence risk/ susceptibility)

• The vulnerability that determines how a host responsds to an agent 

Person (Epidemiological variables that influence risk/ susceptibility)

• Family, health, age, sex, race, marital status, previous illness/immun status etc

• Education, occupation, immigration, socioeconomic status, lifestyle practices

Time (Epidemiological variables that influence risk/ susceptibility)

Cyclical or seasonal variations

Place (Epidemiological variables that influence risk/ susceptibility

• Regional, rural/urban. Population density, specific geographical charcteristics 

Relative risk ratio 

• Measures the risk of developing a condition 

• Relative risk of 1.0 means that the risk for exposd and non-exposd is the same. The higher the relative risk. The greater the potential for developing the condition

The relative risk ratio measures…

• Incidence rate in exposed people/ incidence rate in non-exposed people 

Prevalence

• Measures burden of disease in a population

  • Influenced by number of people and duration of condition

  • Used for health planning, primary prevention

Prevalence formula 

• Number of people in the given population with the condition/ Total number of people in population at that time

Period prevalence defined 

• Existence of a condition during a period of time

Point prevalence defined 

• Existence of a condition at a particular point in time 

• Inferred if no time period provided

Incidence

• Also called “occurrence” or “attack rate”

• Measures the probability that people without a condition will develop the conditon over a period of time

• Measures the pace at which NEW cases develop

• Useful for identifying outbreaks

Incidence formula 

• Number of new cases in a population in a given period/ Total number of the population in that period 

  • Sometimes the denominator is designated as mid-year, depending on what is being studied 

Pre-pathogenesis

• Studies the natural history/pattern of disease

• Also known as the incubaton period 

• The host may be exposed 

• Access to determinants of health/other stressor influences susceptibility

Health practitioner focuses on (pre-pathogenesis) 

• Primary prevention strategies to promote optimal health 

Pathogenesis 

• Studies the natural history/pattern of disease 

• Person begins to react 

• may/not be symptomatic, however disease is present

Health practitioners focus on (Pathogenesis) 

• Secondary prevention to allow for early dx & rx (e.g screening) and/or prevent complications & disability

Late pathogenesis

• Pathogenesis period ends with recovery, disability or death 

Health practitioners focus on (late pathogenesis) 

• Tertiary prevention to provide education to adjust to new health realities; adaptation strategies; palliation 

Associaton 

• Reasonable evidence of the connection between a stressor or environmental factor & disease or health challenge

Causation

• confirmed, definite, statistical relationship

  • Requires certain factors to be both necessary and sufficient

5 Criteria for a cause → effect relationship

• timing

• strength

• prevalence 

• Relationship to other risk factors

• Plausibility

Timing (5 Criteria for a cause → effect relationship)

• Exposure occurs before the development of diseases or during its progression 

Strength (5 Criteria for a cause → effect relationship)

• Is dose-dependent 

• Cessation of exposure can modify the disease

Prevalence (5 Criteria for a cause → effect relationship)

• Occurs in multiple populations 

Relationship to other risk factors (5 Criteria for a cause → effect relationship)

•  Is independent 

• Can also act synergistically

Plausibility (5 Criteria for a cause → effect relationship)

•  Produces structural or functional changes, which are events in the mechanism of disease

 Emergencies & disasters (disaster/emergency control and management) 

• Epidemics/pandemics (communicable disease 

• Natural - tsunamis, hurricanes, floods, wildfires, earthquakes etc

• Man-made- e.g bioterrorism, explosions, collapses, water/flood contamination

Steps on Responding to a disaster/emergency 

• prevention

• mitigation

• preparedness

• response

• recovery 

Prevention (Responding to a disaster/emergency)

• Activities to prevent or avoid an emergency or disaster 

Mitigation (Responding to a disaster/emergency)

• Actions that can reduce the impact of an emergency or disaster 

Preparedness (Responding to a disaster/emergency)

• Measures in place before a problem occurs 

  • E.g plans, tools, protocols 

Response (Responding to a disaster/emergency)

• Coordinated actions are necessary to respond 

Recovery (Responding to a disaster/emergency)

• Activities to help the community recover 

Collaborative efforts in management of communicable diseases 

• Prevent (vaccination) 

• Control spread (treatment & quarantine) 

• Monitor: timely reporting, contact tracing 

Public safety & emergency preparedness in Canada

• In Canada, federal, provincial and local municipalities ned to be prepared for and respond to disasters  

• 1st responsibility: municipal → 2nd responsibility: proviniical → 3rd respoonsibility: federal 

Three levels of disease prevention and protection

• Primary: health promotion/prevention

• Secondary: target early diiagnosis

• Tertiary: limiting disability 

Primary prevention 

• Preventing disease: Trying to prevent people from getting a disease 

• Knowledge- research etc., to better understand transmission

• Policies - food, water, sanitation 

• Vaccination programs 

• Strong infection control protocols 

• Health education/ communication about transmission

• Passive surveillance to identify trends

Secondary prevention 

• Controlling disease: trying to detect a disease early and prevent it from getting worse

• Strong public health outbreak policies

• Education about transmission 

• Screening 

• Contact tracing 

• Active & passive surveillance

• Quarantine as necessary 

• Enforcing health hygiene measures 

Tertiary prevention 

• Treating disease: managing disease post-diagnosis to slow or stop disease progression through measures such as chemotherapy, rehabilitation, and screening for complications 

• Improving quality of life and reducing the symptoms of a disease 

• Treatment of illnesses

• Support of ill individuals

Elimination 

• Reduction in the regional incidence of a disease to zero as a result of deliberate efforts. Control efforts would need to be continued 

Eradication 

• Reduction in the worldwide incidence to zero as a result of deliberate efforts, obviating the need for further control measures

Methods for eradication 

• Scientific feasibility 

• Effective intervention

• Political will

Effective intervention (methods for eradication)

• Vaccine 

• Curative treatment 

• Elimination of the vector 

  • Ideally, this should be safe, inexpensive, long-lasting, and easily deployed 

Political will (methods for eradication)

• Perceived burden of disease

• Expected cost of eradication 

• Necessity for eradication rather than control 

• Synergy of eradication efforts with other interventions

 Immunization in Canada 

• In the last 50 years, immunization has saved more lives in Canada than any other health intervention 

• A 70% coverage rate is required to break the chain of transmission

Online claims about vaccines 

• Poisonous and cause idiopathic illnesses

• Vaccines contain anti-freeze, ether, formaldehyde, mercury

• Illnesses attributed to vaccines include: AIDS, asthma, autism, cancers, diabetes, fibromyalgia, leukemia, lupus, SIDS

• Studies showing no link between vaccines and illness such as autism are ignored

• Questioning whether vaccines actually conferred immunity was common(88%). Rationale cited is that vaccinated people still contract the diseases (Kata, A., 2010).

Key steps in communicable disease control 

• Find out if there’s a case

• Confirm the case

• Decide if there is an outbreak

• Establish an outbreak team

• Investigate the outbreak

• Analyze and establish control measures for outbreak

• Increase surveillance

  • Active (increased surveillance)- screening tools, interviews, systems to identify disease when people demonstrate symptoms

  • Passive (increased surveillance)– provider reporting; lab results of reportable illnesses

• Multi-level Communication— Timely public communication

• Report diseases

• Review and revise the control plan as needed

• Final evaluation at the end 

Control & management of communicable disease

• Understand the nature of the disease

• Establish a case definition (H1N1)

Understand the nature of the disease (Control & manage communicable disease, PHAC 2009)

• Etiology (agent)- e.g H1N1

• Incubation period -1-4 days 

• Infective period- up to 7 days from the onset of symptoms to 24 hours after all symptoms resolve 

Establish a case definition (H1N1) (Control & manage communicable disease, PHAC 2009)

• Fever, cough- maybe mild for those <5 and <65 

• One of: sore throat, muscle, joint pain or weakness

• Children <5: GI symptoms

Attention to SDOH and susceptibility in disease control/management

• Where we live 

• Where we work 

• Access to health resources 

• Level of health literacy

Attention to vulnerable population in disease control/management

• Consider: how do we ensure that vulnerable populations are prepared for a disaster/included in disaster planning? 

  • Elderly 

  • Pregnant women

  • Children 

  • ESL or non-English speakers

  • People with cognitive challenges/disabilities

  • People with physical challenges and mental health challenges

 Reportable illnesses 

• In Canada: maintaining the notifiable disease information system is a provincial and territorial responsibility.

• WHO specifies a number of diseases that must be reported worldwide.

• Some provincial and territorial public health authorities require physicians to report when they suspect an outbreak of any infectious disease.

  • Some lists include non-infectious diseases that can be caused by environmental hazards, such as poisoning with heavy metals or with carbon monoxide

Physicians' role in reporting illnesses

• Are required to notify the public health authority immediately when history and clinical examination causes them to suspect a notifiable disease.

• Laboratories notify the public health authority of cases of notifiable disease when test results are positive.

PHAC requires illness to be reported based on the illness

• Interest to national or international regulations or prevention programs

• National incidence

• Severity

• Communicability

• Potential to cause outbreaks

• Socio-economic costs of its cases

• Preventability

• Risk it poses in the public perception

• Need for a public health response

• Evidence that its pattern is changing.

Information to accompany reporting 

• Requires information 

  • About the person 

  • Symptoms & date of onset of presenting illness 

  • Travel history 

• May also include: 

  • Social history 

  • Sexual history 

  • Diagnostic tests to date

  • Prescribed RX

System level (who is involved in communicable disease control/management)

• Local, regional and national public health agencies; MOH

• Media

• Academics/researchers providing scientific data

• Other government agencies as relevant

Organizational level (who is involved in communicable disease control/management)

• Local public health units; LHINS in Ont.

• Hospital decision-making bodies

• Occupational health/infection control experts

Client level (who is involved in communicable disease control/management)

• Health care workers

• Emergency departments

• Specialty clinics (HIV, STD, Tropical disease)

• Laboratories

Emergency Management in Canada 

• Begins at the local level:

• Province only intervenes if local level requests aid.

• Federal intervention only occurs if capacity is exceeded at local & provincial

  • Federal aid - tailored to the situation & does not exceed what is necessary for the situation

  • PHAC works with provinces & territories to provide leadership to coordinate a unified response to public health emergencies

• Note: US response begins at federal level (FEMA)

Emergencies Act (Relevant federal legislation)

• Provides a basis for planning & programming to address disasters

• Addresses the need for cooperation between the provinces & territories at the federal level to establish responsibilities & need for public awareness, AND provides a structure for training & education