Epidemiologic Approach & Disease Occurrence PDF

EPIDEMIOLOGIC APPROACH & DISEASE OCCURRENCE NURS 1113 – Epidemiology (Weeks 2-3) Mickelle EmanuelFrith February, 2024 OBJECTIVES At the end of the class students should be able to: Discuss the epidemiological approach Explain the concepts of disease occurrence  Causation  Models  Outline of the n...

EPIDEMIOLOGIC APPROACH & DISEASE OCCURRENCE NURS 1113 – Epidemiology (Weeks 2-3) Mickelle EmanuelFrith February, 2024 OBJECTIVES At the end of the class students should be able to: Discuss the epidemiological approach Explain the concepts of disease occurrence  Causation  Models  Outline of the natural history of disease  Levels of prevention Describe the natural history and spectrum of disease Examine Jamaica’s epidemiological profile Discuss national health goals and strategies 2 THE EPIDEMIOLOGICAL APPROACH Practice of epidemiology follows a systematic approach which involves defining a case which is then followed by: COMPARIN G COUNTING DIVIDING Cases or health events are counted and described in terms of time, place, and person The number of cases are divided by an appropriate denominator to calculate rates These rates are compared over time or, for different groups of people Establishing case definition  Counting  Dividing  Comparing 3 ] WHAT IS A CASE DEFINITION? “Set of standard criteria for deciding whether a person has a particular disease, syndrome or other health condition” Before counting cases, epidemiologist must determine what comprises characteristics of a case (i.e., formulates a case definition) Case definitions used for national surveillance are usually developed and adopted as national standards to enable comparability Looks at the “What” of epidemiology 4 ] CASE DEFINITION The use of standard case definition ensures that all cases are diagnosed in the same way regardless of when or where the case occurred or who identified the case When standard case definitions are used to characterize cases and a difference in disease occurrence is observed in an individual case, the difference is likely to be a real difference rather than a variation in how cases were diagnosed 5 CASE DEFINITIONS Case definitions used in local outbreak investigations are frequently tailored to the local situation In such situations, laboratory confirmation may be required where the services are available but likely would not be required if the services were not available 6 COMPONENTS OF CASE DEFINITION FOR OUTBREAK INVESTIGATIONS Consist of clinical criteria and sometimes limitations on time, place and person (to reflect the scope of the outbreak) Clinical criteria usually include: Confirmatory laboratory tests (if available) or, Combinations of symptoms (subjective complaints), signs (objective physical findings), and other findings 7 ] CRITERIA IN CASE DEFINITIONS May have several sets of criteria, depending on the degree of certainty of the diagnosis Example: During an investigation of a possible case or outbreak of measles, a person with a fever and rash might be classified as being a: suspect case of measles, probable case of measles, or confirmed case of measles depending on what evidence of measles is present 8 EXAMPLE OF A CASE DEFINITION OF MEASLES (RUBEOLA) 1996 Clinical Description Illness characterized by all of the following: Generalized rash for ≥3 days Temperature ≥ 101.0°F (38.3°C) Cough, coryza, or conjunctivitis Lab Criteria Positive serologic test for measles immunoglobulin M antibody or, Significant rise in measles antibody level by any standard serologic assay, or, Isolation of measles virus from a clinical specimen Case Classification Suspect: Any febrile illness accompanied by rash Probable: Meets clinical case definition, has noncontributory or no serologic or virologic testing, and is not epidemiologically linked to a confirmed case Confirmed: Laboratory confirmed or, meets clinical case definition and is epidemiologically linked to a confirmed case 9 CASE DEFINITIONS Case may be classified as “suspect” or “probable” while awaiting lab results Case is re-classified after lab result is obtained as “not a case” or “confirmed” depending on result 10 CASE DEFINITIONS Some cases are permanently labelled “suspect” or “probable” if officials believe that lab test on every person with consistent clinical picture and history of exposure is unnecessary or wasteful Can change as more information becomes available about it Happened in the case of SARS which had a series of modification as studies revealed new information about the condition SARS – Severe Acute Respiratory Syndrome 11 CASE DEFINITIONS Case definitions may vary according to purpose for classifying the occurrences of a disease Sensitive case definition (“broad” or “loose”) is used for rare but potentially severe communicable diseases (e.g. anthrax) to capture most or all true cases Specific case definition (strict) is used to ensure that only persons who actually have the disease are included in the investigation of the causes of a disease outbreak Disadvantage – may underestimate the total number of cases 12 COUNTS (NUMBERS) Identifying and counting cases is a basic task in public health Counts are obtained from case reports submitted to the health department by health care providers and laboratories Counts allow for the determination of the extent and patterns of disease occurrence by time, place and person as well as identify clusters or outbreaks of disease in a community (measure and describe morbidity) 13 ] COUNTS (NUMBERS) While counts are valuable for health planning (e.g. for allocating resources), simple counts do not provide all the information that is necessary For some purposes, counts must be put in context based on the population hence, counts are sometimes converted into rates 14 ] RATES Rate = number of cases unit of time (K) size of population at risk x 𝑥 “Measures that relate the number of × 𝑘 cases (counts) during a specified point 𝑦 in time or period of time (usually year) X = number of times an event has occurred during a to the size of the population in which specific interval of time the cases occurred” Y = number of persons exposed to the risk of the event during the same interval Most commonly used statistical tool in epidemiology K = some round number (100, 1000, 10,000, 100,000... Depending on the magnitude of x and y 15 USES OF RATES Compare frequency of disease in different areas whose populations differ in size Compare disease occurrence during different periods of time Identify persons in a community at increased risk for a disease or health-related event so that targeted interventions can be initiated 16 TYPES OF RATES INCLUDE: Birth rate Morbidity rate Attack rate Mortality rate Infant mortality rate Maternal mortality rate 17 CONCEPTS OF DISEASE OCCURRENCE 18 CONCEPTS OF DISEASE OCCURRENCE Disease and other health events do not occur randomly in a population Diseases and other health events are more likely to occur in some members of the population than others because of non-random distribution of risk factors Epidemiology is used to identify factors that place some persons at greater risk than others 19 DISEASE CAUSATION A number of epidemiologic methods are used to search for causes of disease. Among the many models proposed are the: Epidemiologic triad Web of causation BEINGS model Group Work (10 minutes) Each group explain one model and give an example The Causal Pie Model 20 EPIDEMIOLOGIC TRIAD Among simplest traditional model for infectious disease Consists of agent (external), host (susceptible) and environment (brings host and agent together) Disease results from interaction between agent and susceptible host in an environment that supports transmission of the agent from a source to that host 21 EPIDEMIOLOGIC TRIAD Agent Biologic – allergens, infectious agents (viruses, bacteria, fungi etc.) Chemical – chemical toxins, dust Physical – trauma, radiation, heat, cold, noise Social and psychologic stressors – socioeconomic issues 22 EPIDEMIOLOGIC TRIAD Environment Extrinsic factors that affect the agent and the opportunity for exposure influences the probability and circumstances of contact between the host and the agent Vector  effective transmitter of diseases. Includes insects, rodents, humans 23 EPIDEMIOLOGIC TRIAD Host Final link in the chain of infection is a susceptible host Susceptibility depends on genetic or constitutional factors, specific immunity, and non-specific factors 24 WEB OF CAUSATION Shift in thinking about disease causation - incorporates the idea of multiple causes of diseases Cases of disease can be prevented by cutting a few strands of the web Factors closest to the disease are usually targeted 25 BEINGS MODEL OF DISEASE CAUSATION Addresses risk factors and preventable causes of diseases Biologic and behavioural Environmental Immunologic Nutritional Genetic Services, social, spiritual 26 THE CAUSAL PIE MODEL Explains when and why biological factors (component causes) have an effect Causal pie consists of: Sufficient cause Component cause Necessary cause 27 THE CAUSAL PIE MODEL Sufficient cause – condition or set of conditions that will produce the event, but it alone does not provide (the whole pie) E.g. sufficient cause for AIDS may consist of engaging in risky sexual behaviour; exposure to an HIV infected person; absence of ARVs Hot water is a sufficient cause of burns, but burns may also be caused by other factors Component cause – each component / exposure in a sufficient cause Necessary cause – condition that MUST be present for an event to occur (found in all cases) E.g. HIV is a necessary cause of AIDS (must be present) 28 THE CAUSAL PIE MODEL Example 29 NATURAL HISTORY OF DISEASE 30 NATURAL HISTORY OF DISEASE “Progression of a disease process in an individual over time in the absence of treatment” Disease process starts with exposure to or an accumulation of factors that capable of causing the disease If no medical intervention, disease process will end with recovery, disability or death Progression may be halted at any point with preventive or therapeutic measures 31 NATURAL HISTORY OF DISEASE TIMELINE Onset of symptoms Pathologic changes Usual time of diagnosis Exposure Stage of susceptibility Stage of sub-clinical disease (Known as Incubation period infectious diseases Latency period - chronic diseases) Adapted from CDC, Principles of Epidemiology Stage of clinical disease (Patient is symptomatic) Stage of recovery, disability or death 32 NATURAL HISTORY OF DISEASE Screening programmes aim to identify disease process during sub-clinical stage – interventions are more likely to be successful Some persons may never progress to clinical stage e.g. carriers Disease may progress from mild to severe or fatal in some persons. This range is called the “spectrum of disease” 33 SPECTRUM OF DISEASE Asymptomatic Person having a condition but showing no signs or symptoms Mild Moderate Severe Carrier Person without apparent disease but is capable of transmitting the agent to others 34 TYPES OF CARRIERS Asymptomatic carrier: Never show symptom during the time affected Incubatory carrier: Capable of transmitting disease before being clinically ill Convalescent carrier: Capable of transmitting disease after clinical state is resolved Chronic carrier: Continues to harbour infectious agent for extended period of time following initial infection 35 CHAIN OF INFECTION 36 CHAIN OF INFECTION Based on the epidemiologic triad Disease is transmitted when an agent leaves its reservoir (or host) through a portal of exit and is conveyed through some mode of transmission and enters through a portal of entry to infect a susceptible host 37 EPI APPROACH 38 Aedes aegypti Aedes albopictus EPI APPROACH - [VHWB-2024] 39 CHAIN OF INFECTION - RESERVOIRS Habitat in which infectious agent normally lives, grows and multiplies; includes human, animals and environment Human Disease transmitted directly from person to person e.g. sexually transmitted diseases, respiratory infections, measles, smallpox* Two types of human reservoirs: asymptomatic cases and carriers Animals Environment Infectious diseases transmissible from Plant, soil, water e.g. vertebrate animals to humans under many fungal agents live normal conditions (zoonoses) e.g. and multiply in the soil anthrax (sheep), rabies (dog) Another group of diseases with animal reservoirs is caused by viruses transmitted by insects and caused by parasites with complex life cycles e.g. malaria (mosquito) 40 CHAIN OF INFECTION - PORTAL OF EXIT Path by which pathogen leaves its host e.g. influenza viruses exit via respiratory tract Usually corresponds to area where agent is localized e.g. influenza viruses exit via the respiratory tract, cholera bacteria exit via faeces, scabies mites exit via skin 42 CHAIN IF INFECTION - MODES OF TRANSMISSION After exiting natural reservoir, agent may be transmitted directly or indirectly Direct Immediate transfer of agent to host via direct contact or droplet spread Direct contact: skin to skin contact, kissing, sexual intercourse, contact with soil or vegetation harbouring agent Droplet spread: large, short-ranged aerosol spray e.g. sneezing, coughing, talking Indirect Agent transmitted from reservoir to host by suspended air particles (airborne), inanimate objects (vehicles) or animate intermediaries (vectors) Arthropods e.g. mosquitoes, fleas, ticks, flies can carry agent by mechanical means (agent does not multiply or undergo physiologic changes in biological host) 43 CHAIN OF INFECTION - PORTAL OF ENTRY Portals include: Provides access to tissues in which agent can multiply or toxin can act Respiratory tract (e.g. influenza) Oro-faecal (e.g. typhoid) Skin (e.g. hookworm) Mucous membrane (e.g. trachoma) Blood (e.g. hepatitis B) 44 CHAIN OF INFECTION – SUSCEPTIBLE HOST Final link in chain of infection Susceptibility influenced by genetic factors, specified acquired immunity among other factors which alter one’s ability to resist infection or limit pathogenicity Protective factors include: first line of defense (skin, mucous membrane, cilia of respiratory tract, cough reflex, gastric acid) and non-specific immune response Influencing factors include: malnutrition, alcoholism, disease or therapy that impairs the non-specific immune response, extremes of age 45 CHAIN OF INFECTION Chain of infection is broken when agent does not find a susceptible host Measures can be employed at any point along the chain If a high proportion of a population is immunized against a specific agent, spread of the disease is limited to the few susceptible hosts by herd immunity Assignment: Class to read up on herd immunity 46 SPECIFIC ACQUIRED IMMUNITY Protective antibodies directed against specific agent Acquired immunity is either active or passive Active immunity – antibodies develop in response to infection (natural active), vaccine or toxoid (artificial active) Passive immunity – antibodies acquired from mother (natural passive) or from injections of antitoxins or immunoglobin (artificial passive) 47 NOSOCOMIAL INFECTIONS 48 EPI APPROACH - [VHWB-2024] NOSOCOMIAL INFECTIONS (HEALTHCARE ASSOCIATED INFECTIONS) Infections acquired in hospital or other health-care facility; manifested 48 hours after admission, within 72 hours of discharge or, up to 30 days post-surgery Pneumonia and surgical site infections (21.8%) are leading causes; gastrointestinal infections (17.1%); urinary tract infections (12.9%) – NCBI, 2018 Incidence trending up due to overcrowding, resistant pathogens, immunocompromised cases 49 NOSOCOMIAL INFECTIONS (HEALTHCARE ASSOCIATED INFECTIONS) Nurses’ Role in the Prevention includes: Careful handwashing Practice and promote strict aseptic technique Nurse infectious patients away from other patients (isolation) Correct use of personal preventive equipment (PPE) 50 REVISION – MATCHING THE TYPES OF CARRIERS 1. Convalescent carrier [A.] Never show symptom during the time affected 2. Chronic carrier [B.] Capable of transmitting disease before being clinically ill 3. Asymptomatic carrier [C.] Continues to harbour infectious agent for extended period of time following initial infection 4. Incubatory carrier [D.] Capable of transmitting disease after clinical state is resolved 51 REVISION – FILL IN THE BLANKS Nosocomial Infection acquired in healthcare facility ____ after admission, ____ after discharge, or up to ____ post-surgery Portal of entry Reservoir Agent 52 PATTERNS OF DISEASE OCCURRENCE 53 PATTERNS OF DISEASE OCCURRENCE Endemic persistent low to moderate disease level of occurrence Hyperendemic persistent high level of occurrence of a disease Epidemic level of disease rises above expected level in a given time period (outbreak) 54 PATTERNS OF DISEASE OCCURRENCE Sporadic irregular pattern of occurrence with occasional cases occurring at irregular intervals Pandemic epidemic occurring over several countries or continents and affecting a large number of people 55 PATTERNS OF DISEASE OCCURRENCE 56 EPIDEMIC DISEASE OCCURRENCE Outbreaks occur when efforts to prevent disease fail The resulting distribution of cases may assume various forms called epidemic curves (aka “epi curve”) Epidemic curves depict distribution of incident cases over time (most evident in infectious diseases) 57 EPIDEMIC DISEASE OCCURRENCE propose hypotheses on the nature of the disease and its mode of transmission The shape of the resulting epidemic curve can be used to: provide information on: - the pattern of spread over time - the magnitude of the outbreak (the number of cases) - the likely incubation period for the condition - can reveal outliers (in time, perhaps in place) 58 ] EPIDEMIC PATTERNS How epidemics spread through a population Classified according to manner in which they spread: common source, propagated, mixed and other Epidemic patterns Common Source Point Intermittent Mixed Propagated Other Continuous 59 ] EPIDEMIC PATTERN Common Source Outbreak People are exposed in a group to a single noxious influence e.g. infectious agent or toxin. Sub-classified as: Point Source Outbreak Intermittent Outbreak Continuous Outbreak 60 ] EPIDEMIC PATTERN Common Source Outbreak Point Source Outbreak - group is exposed for a brief period in which everyone who gets ill develops disease in one incubation period E.g. food contaminated with Staphylococcus aureus Epidemic curve – single curve with steep upward slope and gradual downward slope 61 ] EPIDEMIC PATTERN Common Source Outbreak Intermittent Outbreak - cases are intermittently exposed over a period of days, weeks, or longer Contaminant emitted at intervals or arises from various sources Epidemic curve shows irregular pattern of cases that reflects the timing and extent of repeated exposures 62 Epidemic Pattern Common Source Outbreak Continuous Outbreak - cases are continuously exposed over a period of days, weeks or longer E.g. exposure to contaminated water supply Epidemic curve wide with flattened peak (indicating longer duration of source and variation in incubation periods between people) 63 ] EPIDEMIC PATTERN Propagated Outbreak Does not have a common source Gradual increasing spread from person to person, usually by direct contact e.g. syphilis; vehicle borne e.g. HIV by sharing needle or; vector borne e.g. dengue; measles Cases occur over more than one incubation period 64 ] EPIDEMIC PATTERN Types of Epidemic Curves 65 ] EPIDEMIC PATTERN Mixed Outbreak Features of both common source outbreak and propagated outbreak Pattern of common source followed by secondary person to person spread Others No features of common source or propagated epidemic Zoonotic and vector borne outbreaks may result where there is sufficiency in the prevalence of infection in host species; presence of vectors and human-vector interaction 66 ] NOTIFIABLE DISEASES 67 ] NOTIFIABLE DISEASES Considered to pose threat to society therefore, of great public health importance Mandatory reporting required on suspicion or diagnosis. Allows for: Counting and distribution of the disease Tracking of disease occurrence and identifying possible outbreaks early Implementing prevention and control measures in a timely manner 68 ] NOTIFIABLE DISEASES Class 1 diseases must be notified within 24 hours (Clinician / Lab  Medical Officer of Health  Ministry of Health)..\Lit\Epi Week 17 (2018) Bulletin_Jamaica.pdf [See Epi Weekly Bulletin] 69 NOTIFIABLE DISEASES Class assignment 70 ] ATTACK RATE Measure of frequency of morbidity, or speed of spread, in an atrisk population. It is used in hypothetical predictions and during actual outbreaks of disease Calculated as the number of people who became ill divided by the number of people at risk for the illness In order to calculate an attack rate, a case definition, or set of criteria to define the disease of interest, must first be developed 71 LEVELS OF PREVENTION 72 LEVELS OF PREVENTION - PRIMARY Reducing exposure of healthy persons to risk factors (e.g. avoid smoking) or, one’s resistance (e.g. immunization) Applied in the absence of disease – [Stage of susceptibility] Modifying existing risk factors 73 ] LEVELS OF PREVENTION - SECONDARY Measures employed for early detection and interruption of the progression of diseases in asymptomatic stage (Stage of subclinical disease) when intervention is effective [Screening, a key role] 74 ] LEVELS OF PREVENTION - TERTIARY Avoidance of complications or disability resulting from current disease Limits social and physical consequences [e.g. control of hypertension to prevent heart disease etc.] – Stage of clinical disease or Stage of recovery / disability 75 ] LEVELS OF PREVENTION - PRIMORDIAL Most recent to be recognized Aims to avoid emergence and establishment of the social, economic and cultural patterns of living that are known to contribute to increase risk of disease. E.g. public policies aimed at avoiding development of hazards detrimental to health Prevention of risk factors beginning with change in social and environmental conditions 76 LEVELS OF PREVENTION 77 TERMS USED IN DESCRIPTION OF INFECTIOUS DISEASE Infectivity the proportion of exposed persons who become infected Pathogenicity proportion of infected persons who develop clinically apparent disease Virulence proportion of persons with clinical disease who become severely ill or die 78 ] GLOBAL EPIDEMIOLOGICAL PROFILE Class assignment Top ten causes of morbidity Top ten causes of mortality 79 80 EPIDEMIOLOGICAL PROFILE OF JAMAICA Increasing rates of chronic diseases (cardiovascular diseases, diabetes mellitus, cancers) – leading causes of death (PAHO, 2016) See HIV Epidemiological Profile 2016 (Ministry of Health & Wellness, Jamaica) 81 EPIDEMIOLOGIC TRANSITION Process by which the pattern of mortality and disease is transformed from one of high mortality among infants and children and episodic famine and epidemic affecting all age groups to one of degenerative and man-made diseases 82 ] JAMAICA POPULATION STRUCTURE 83 84 NATIONAL HEALTH GOALS AND STRATEGIES – CLASS DISCUSSION Mission / vision statement Vision 2030 (Ten Year Strategic Plan 2019-2030) National Development Plan National Health Fund 85 ] NATIONAL HEALTH GOALS AND STRATEGIES Weekly Surveillance Bulletin Jamaica Move Free Health Care 86 SUMMARY 87