DESCRIPTIVE EPIDEMIOLOGY
Describe and summarize disease pattern (person, place and time) to generate hypothesis. Does not use comparison groups.
Uses of Descriptive Study
Epidemiologists - Identification of factors that possible contribute to (or inhibit) disease development that can be reduced/eliminated/altered/prevented
Public Health Administrators - Knowledge of the burden of the disease (i.e., which population or subpopulations are affected) that is necessary for evidenced based decision in fund allocation for planning
Sources of Data for Descriptive Studies - Census, vital records, surveys, patient records from hospitals and clinics, employment health records
Classification of Descriptive Study Designs according to type of data collected
-individual (case report/series and prevalence survey)
-aggregate/group (ecological)
TYPES OF DESCRIPTIVE STUDY DESIGN
- Case Report - A study of one diseased individual. Typically, an uncommon disease or set of sympotms. The study design would not require a comparison.
- Case Series - A study of multiple occurrences of unusual cases that have similar characteristics. Investigators can calculate the frequency of symptoms or characteristics among the cases.
- Prevalence Survey - A study that determines the proportion of individuals with disease (or rather health event) in a defined population at a given time point. Provides "snapshot" of the population's health experience at a specified time.
- Ecologic Study - A study in which at least one variable, either an exposure or the outcome, is measured at the group (not individual) level.
ANALYTIC EPIDEMIOLOGY
The hallmark feature of an analytic epidemiologic study:
Use of an appropriate comparison group to estimate counterfactual scenario
- Observational vs Experimental - absence or presence of manipulation of the exposure variable
- Cross-sectional vs Longitudinal - exposure and outcome relate to one or two time points in the life of the subject
- Retrospective vs Prospective - direction of inquiry on the presence of exposure and outcome (E to O/O to E)
OBSERVATIONAL
- Cross-sectional
-a study in which a sample of persons from a population are enrolled and their exposures and health outcomes are measured simultaneously
-It is more useful for descriptive epidemiology than it is for analytic epidemiology
-It is synonymous with survey
Advantage
- usually representative samples used;
- less expensive and time consuming
key feature of a cross-sectional study: It usually provides information on prevalence rather than incidence
EXAMPLE
Representative sample of residents were telephoned and asked how much they exercise each week and whether they currently have (have ever been diagnosed with) heart disease
- Case-control
-An observational analytic study that identifies individuals who develop the disease (cases) and individuals without the disease (controls), and then determines the previous exposure for each case and control.
-The case group is composed only of individuals known to have the disease or outcome; the control group is drawn from a comparable population who do NOT have the disease or outcome.
-We then compare the odds of exposure between cases and controls. The measure of association for a case-control study is typically an odds ratio.
-A case-control study is stronger than a cross-sectional study in establishing individual-level causality because we are more certain that exposure preceded the disease outcome.
EXAMPLE
- Persons diagnosed with new-onset Lyme disease were asked how often they walk through woods, use insect repellant, wear short sleeves and pants, etc. Twice as many patients without Lyme disease from the same physician's practice were asked the same questions, and the responses in the two groups were compared.
- British investigators conducted a study to compare measles-mumps-rubella (MMR) vaccine history among 1,294 children with pervasive development disorder (e.g., autism and Asperger's syndrome) and 4,469 children without such disorders. (They found no association.) This is an example of which type(s) of study
cohort study vs case-control study - Subjects are enrolled or categorized on the basis of their exposure status in a cohort study but not in a case-control study
- Cohort
-an observational analytic study in which enrollment is based on status of exposure to a certain factor or membership in a certain group. Populations are followed, and disease, death, or other health-related outcomes are documented and compared.
-Cohort studies can be either prospective (Investigator in present time; outcome has yet to occur in the FUTURE) or retrospective (Investigator in present time; Exposure and Outcome has already occurred in recent PAST.)
EXAMPLE
- The Iowa Women's Health Study, in which researchers enrolled 41,837 women in 1986 and collected exposure and lifestyle information to assess the relationship between these factors and subsequent occurrence of cancer.
- Occurrence of cancer was identified between April 1991 and July 2002 for 50,000 troops who served in the first Gulf War (ended April 1991) and 50,000 troops who served elsewhere during the same period.
EXPERIMENTAL
- a study in which the investigator specifies the type of exposure for each person (clinical trial) or community (community trial) then follows the persons' or communities' health status to determine the effects of the exposure.
Advantage of Experimental research - Permits cause-and-effect relationships
EXAMPLE
- Subjects were children enrolled in a health maintenance organization. At 2 months, each child was randomly given one of two types of a new vaccine against rotavirus infection. Parents were called by a nurse two weeks later and asked whether the children had experienced any of a list of side-effects.
- A study in which children are randomly assigned to receive either a newly formulated vaccine or the currently available vaccine and are followed to monitor for side effects and effectiveness of each vaccine.
Vaccine efficacy measures - The proportionate reduction in disease among vaccinees.
between subjects design (parallel controlled trial) - a different group of subjects is tested under each condition
within subjects design (cross over trial) - an experimental design in which the same subjects are tested under each condition
clinical trial - (n) a study in which researchers test a treatment on volunteers and carefully monitor the effects
community trials - observational trials in which participants voluntarily participate in controlled studies
Affected by
-population dynamics
-secular trends
-nonintervention influences
Therapeutic effect - Desired benefit of a medication, treatment, or procedure.
prophylactic effect - a medication designed to prevent a disease from occurring
Intent to treat - -All patients who are randomized are included in data analysis
per protocol analysis - Includes only those who completed the treatment originally allocated
Continuous outcome variables - Enhances POWER of study; smaller sample size
dichotomous outcome variables - Power depends on NUMBER OF EVENTS rather than no of subjects
Run-in design -
factorial design - an experiment or quasi-experiment that includes more than one independent variable
matched pairs design - create blocks by matching pairs of similar experimental units
Pre-randomization -
Group randomization - Groups or naturally forming clusters are randomly assigned the intervention.
time-series design - a type of quasi-experimental design in which multiple observations are made of a single group
cross-over design - when all groups in a study at some point receive both placebo and experimental treatment
MEASURES OF ASSOCIATION
FORMULAS
- Odds Ratio (for Case Control) - ad/bc
- Risk Ratio or Rate Ratio (for Cohort) - [a/(a+b)]/[c/(c+d)]
- Prevalence in exposed group (P1) - a/a+b
- Prevalence in unexposed group (P0) - c/c+d
- Prevalence Ratio - P1/P0
- Prevalence difference - P1-P0
- incidence proportion in exposed (IE) - a/a+b
- incidence proportion in unexposed (IU) - c/c+d
- Incidence rate in exposed (IRE) - a/L1
- Incidence rate in unexposed (IRU) - c/L0
- Risk Difference or Rate Difference (RD) -
- Risk: IE-IU
- Rate: IRE-IRU
- Attributable risk exposed (ARE) - IE-IU/IE x 100
Interpretation: 85% of the popn developed dse due to the exposure
- Attributable no.= ARE x exposed sick population
Interpretation: 25% of the popn developed dse that is not attributable to the exposure
- Population attributable risk (PAR) - incidence in population - incidence in unexposed / incidence in population x 100
Interpretation: 75% of those who developed dse can be attributed to exposure
- Attributable no.= PAR x total population sick
- Attributable risk - Measure of the amt of dse or death that could be attributed to the exposure
RESULT
=1 - No association
Interpretation: The factor is not associated with the disease
>1 - Harmful association/risk factor
Interpretation:
Those exposed to the factor are X times more likely to develop the dse comparef to those not exposed to the factor or
The risk of dse is X times more for those exposed to the factor comparef to those who are unexposed
<1 - Protective/beneficial association
Interpretation:
Those with the factor are X times less likely to develop the dse compared to those without the factor Or
The risk of dse is X times less for those exposed to the factor comparef to those who are unexposed
SYSTEMATIC ERROR
BIAS
-a systematic deviation of results or inferences from the truth or processes leading to such systematic deviation;
-any systematic tendency in the collection, analysis, interpretation, publication, or review of data that can lead to conclusions that are systematically different from the truth.
-In epidemiology, does not imply intentional deviation.
Types of Bias
-
Information Bias (misclassification bias) - systematic difference in the collection of data regarding the participants in a study (e.g., about exposures in a case-control study, or about health outcomes in a cohort study) that leads to an incorrect result (e.g., risk ratio or odds ratio) or inference.
- Differential misclassification - amount of misclassification is not equal; bias cannot be predicted
- Nondifferential misclassification - amount of misclassification is equal; bias usually towards null
-
Selection Bias - systematic difference in the enrollment of participants in a study that leads to an incorrect result (e.g., risk ratio or odds ratio) or inference.
-
CONFOUNDING
- a distortion of the association between an exposure and an outcome that occurs when the study groups differ with respect to other factors that influence the outcome.
Confounder - an extraneous variable that wholly or partially accounts for the observed effect of a risk factor on disease status.. The presence of a confounder can lead to inaccurate results
Three conditions that must be present for confounding to occur:
1. The confounding factor must be associated with both the risk factor of interest and the outcome.
2. The confounding factor must be distributed unequally among the groups being compared.
3. A confounder cannot be an intermediary step in the causal pathway from the exposure of interest to the outcome of interest.
Controlling Confounders
design stage:
-restriction
-matching
-randomization in clinical trials
analysis stage:
-Stratification
- Multiple variable regression analysis
Healthy Worker Effect - This term refers to the observation that employed populations tend to have a lower mortality experience than the general population
CAUSATION
Causation - A cause and effect relationship in which one variable controls the changes in another variable. Cause and effect. (E to D)
Association - Identifiable relationship between exposure and dse or co-existence. It does not always indicate that there is a cause and effect relationship. (E and D)
Causal - Alteration in the frequency or quality of one event is followed by a change in the other
Non-causal - Disease causes exposure; disease and exposure both associated with a third factor (due to confounding)
Sufficient Cause - A condition that guarantees the occurrence of a disorder (pie)
Necessary Cause - a condition that must be present for the effect to occur
Component Cause - a factor that contributes to a sufficient cause (slice of a pie)
Induction period - Period of time from causal action until dse initiation
latent period - Period from disease initiation to detection. Dependent on detection effort. Some interventions can advance or postpone onset of dse.
Imperical induction period - Combined induction and latent period
Making judgment about causality
1. Determine presence of validity of statistical assoc. (rule out chance, bias ,confounding as an explanation of the observed assoc)
2. Determine if observed assoc is causal (consider totality of evidence in literature)
Bradford Hill criteria for causality
- Specificity
- Theoretical Plausibility
- Temporality
- Strength of association
- Consistentency
- Dose-Response Relationship (biological gradient)
- coherence
RESEARCH ETHICS
- A set of guidelines to assist the researcher in conducting ethical research
- confidentiality, informed consent, honesty
OUTBREAK INVESTIGATION
Outbreak -upsurge of cases (of a disease) in a defined geographic region or easily defined population; epidemic limited to localized increase in the incidence of the disease
Epidemic -occurrence of more cases of diseas tha expected over a larger area than that experienced in an outbreak
Endemic Habitual presence of a disease within a given geographic area
Ongoing, constant mild to moderate elevation of a disease above a baseline of zero
Hyperendemic Refers to a constant presence of a very high incidence of disease or infection.
Sporadic disease that occurs infrequently and irregularly
Pandemic an epidemic that is geographically widespread
Disease cluster aggregation of cases in a given area over a period without regard o whether the number of cases is more than expected
Epidemic Patterns
1. Common-source -- a group of persons are all exposed to an infectious agent or a toxin from the same source
-Point
-If the group is exposed over a relatively short period, so that everyone who becomes ill does so within one incubation period
-epidemic curve: steep upslope and a more gradual downslope (a so-called "log-normal distribution")
-Continuous
- case-patients may have been exposed over a period of days, weeks, or longer.
-epidemic curve: range of exposures and range of incubation periods (prolonged) tend to flatten and widen the peaks (plateau)
-Intermittent
-often has a pattern reflecting the intermittent nature of the exposure.
-exposure to agent is SPORADIC
-epidemic curve: irregularly jagged
2. Propagated - transmission is by direct person-to-person contact
-epidemic curve: series of progressively taller peaks one IP apart
3. Mixed
Factors affecting the decision to mount an Outbreak Investigation
-ability to confirm the observed cases is significantly greater than expected
- scale and severity of the outbreak
-whether the outbreak disproportionately affects an identifiable subgroup
-potential for spread
-political and public relations considerations
-availability of resources
Steps in Outbreak Investigation
1. Prepare for field work
2. Establish the existence of an outbreak
3. Verify the diagnosis
4. Establish a working case definition and search for additional cases
5. Conduct descriptive epidemiology
6. Develop hypotheses
7. Evaluate hypotheses epidemiologically
8. As necessary, reconsider, refine, and re-evaluate hypotheses and conduct additional studies
9. Implement control and prevention measures
10. Communicate findings
Case Definition (Outbreak Investigation)
-a standard set of criteria for deciding whether an individual should be classified as having the health condition of interest.
-must not include the exposure or risk factor you are interested in evaluating.
- includes criteria for person, place, time, and clinical features. These should be specific to the outbreak under investigation
Confirmed usually must have laboratory verification
*Example:A suspected or probable case with laboratory confirmation.
Probable (Suspected) usually has typical clinical features of the disease without laboratory confirmation
*Example: A suspected case as defined above and turbid CSF (with or without positive Gram stain) or ongoing epidemic and epidemiological link to a confirmed case.
Possible usually has fewer of the typical clinical features
*Example: A case that meets the clinical case definition.
Relative priority of investigative and control efforts during an outbreak
Agent
Mode of Transmission
Known
Unknown
Known
Investigation+
Control+++
Investigation+++
Control+
Unknown
Investigation+++
Control+++
Investigation+++
Control+
Agencies responsible for outbreak investigation
1. local health departments (CESU/MESU)
2. Higher level health agencies (CHD via RESU and/or DOH through Epidemiology Bueau
-investigation requires additional resources
-outbreak attracts substantial public concern
-outbreak is associated with high attack rate and serious complications (hospitalization or death)
Objective of outbreak investigation
- assess range and extent of the outbreak
-reduce the no. of cases associated with the outbreak by identifying and eliminating the source of the problem
-identify new disease syndromes
-identify new causes of known disease syndromes
-assess the effectiveness of currently employed prevention strategies
-address liability concerns
-provide good public relations and educate the public
Describing outbreak by TIME
Epidemic curve
-visual display of the magnitude and time trend of the outbreak, allowing epidemiologist to differentiate between epidemic and endemic disease
Information gleaned from Epidemic Curve
1. Probable period of exposure
2. Nature of epidemic
3. Future course of epidemic
4. Effectiveness and timeliness of prevention and control measures
Describe outbreak by PLACE
1. simple dot maps (evidence of clustering; equal pop. sizes)
2. maps of area-specific rates (unequal pop. sizes)
Describe outbreak by PERSON
- high-risk groups
- age and sex
- person factors relevant to outbreak investigation
Quantitative Epidemiologic investigation
1. Retrospective Cohort Study
-small well circumscribed outbreaks
- high incidence of disease
2. Case Control Study
- large poorly circumscribed outbreaks
- low incidence of disease (rare disease)
Other information collected in outbreak investigation
-Identifying information
-Demographic information
-Clinical information
-Risk factor information
-Reporter information
Line list
-a table that provides information of specific cases
- each column represents an important variable, such as name or identification number, age, sex, case classification, etc., while each row represents a different case
COMMUNICABLE DISIEASES
-diseases that are: infectious, transmissible and/or contagious
Infectivity ability of an agent to invade and multiply in the host
Pathogenicity the ability of an agent to cause disease
Virulence ability of an agent to cause complications and /or death in the diseased host
Toxigenicity ability of an agent to produce toxins
Resistance ability of an agent to survive in adverse environmental conditions
Antigenicity ability of an agent to induce antibody production in host
Attack Rate Sick/exposed
Secondary Attack Rate The attack rate in susceptible people who have been exposed to a primary case.
Index Case First case in an epidemic
Coprimaries cases related to INDEX CASE so closely in time that it is thought to belong to the same generation of cases as index case
Primary Case The individual who brings the disease into the population.
Secondary Case People infected from the primary cases.
Passive Carrier (asymptomatic or healthy carrier) Infected person with no s/sx but is shedding the disease agent
Chronic carrier - those who continue to harbor a pathogen such as hepatitis B virus or Salmonella Typhi, the causative agent of typhoid fever, for months or even years after their initial infection.
Incubatory Carrier - those who can transmit the agent during the incubation period before clinical illness begins
Convalescent Carrier - individuals who harbor the pathogen, and although are in the recovery phase, are still infectious
Active Carrier with s/sx and pathogen present
Incubation Period (communicable disease) time from infection to development of symptomatic disease
Incubation Period (noncommunicable disease) time from causal action until disease initiation
latency period (communicable disease) time interval from infection to development of infectiousness
latency period (noncommunicable disease) time interval from disease occurrence to disease detection
Big 3 CD in Philippines
1. HIV/AIDS
2. TB
3. Malaria
Emerging Infectious Diseases may refer to:
-new diseases
-old diseases spreading to new geographic areas
-diseases which have increased in incidence in the last few decades
-diseases that are expected to increase in incidence in the future
Example of Emerging Infectious Diseases
SARS-CoV
MERS-CoV
West Nile Virus
Chikungunya
Ebola
HIV
Hepa C
Reemerging Infectious Diseases
Diseases which have been previously put under control but have recently increased in incidence because of:
1. microbial adaptation and resistance to drugs
2. vector resistance to pesticides
3. changing host characteristics and behavior
4. changing environments
Example of Reemerging Infectious Diseases Influenza
MDR-TB
XDR-TB
Gonorrhea
Cholera
Dengue
Malaria
Measles
Neglected Tropical Diseases (NTDs)
Examples
Schistosomiasis
Soil-transmitted helminthiiasis (STH)
Lymphatic filariasis (LF)
Leptospirosis
Leprosy
Rabies
CD Focus in the Philippines
- Big 3 CD in Philippines
- Emerging and Reemerging Infectious Diseases
- Food and Waterborne Diseases
- Neglected Tropical Diseases
EPIDEMIOLOGIC TRIAD
Agent NECESSARY FACTOR
presence or absence of which is a must for disease to ensue
*Biological
*Chemical
*Physical
Host TARGET
inherent characteristics influence vulnerability to disease
*Socioeconomic status
*Demographoc
*Genetic
Environment SUMMARY
of all external conditions contributing to disease development
*Biological
*Physical
*Social
Chain of infection
- Infectious agent - Something that infiltrates another living thing such as bacteria, viruses, fungi, and parasites
- Reservoir - A place where the pathogen grows and reproduces
- portal of exit - a way for the causative agent to be released from the reservoir
- mode of transmission - contact, droplet, air, vehicles, or vectorborne
- portal of entry - the route that a microbe takes to enter the tissues of the body to initiate an infection
- susceptible host - a person likely to get an infection or disease, usually because body defenses are weak
Isolation - separating those WITH DISEASE from those dont have the disease during INFECTIOUS PERIOD
*GOAL: prevent spread of disease*
Quarantine - separating those who are HEALTHY&EXPOSED for observation during INCUBATION PERIOD
*GOAL: determine if exposure will lead to disease*
Elimination - reduction to zero of the incidence of disease or infection in a LARGE GEOGRAPHICAL AREA
Eradication - elimination of the occurrence of a given disease, even in the absence of all preventive measures
-permanent reduction to zero of the WORLDWIDE/GLOBAL incidence of infection caused by a specific agent as a result of deliberate efforts; intervention measures are no longer needed.
*Example: smallpox.
Herd Immunity - proportion of immunes in the population exceed at a certain level; such that the disease agent may be unable to maintain itself and will cease to be a public health problem for a given area or region
NON-COMMUNICABLE DISIEASES
Cannot be transmitted from an infected person to a susceptible healthy one (non infectious, chronic, degenerative and lifestyle related)
MAIN TYPES OF NCD
1. CVD
a. heart attack
b. Stroke
2. Cancer
3. Diabetes
4. Chronic lung disease
a. COPD
b. Asthma
Challenges posed NCDs
1. hidden, misunderstood and under-recorded
2. unprecedented health-care need in LMICs (low and middle income countries)
3. affect the pace and the progress of the economic growth
4. impact the international efforts at development
Global Burden of NCD
- Currently the leading cause of death worldwide
- 28 M (74%) in LMICs
- 16 M (42%) premature mortality (deaths under 70s)
PH Burden of NCD
1. CVD
2. Malignant Neoplasms
3. CD
Disability Adjusted Life Year
-a common currency by which deaths and disability may be measured
-measures the gap between current health status and an ideal situation one lives into old age, free of disease and disability
*DALYs= YLL+YLD*
Risk Factors of NCDs
- Sociocultural Factors - globalization, urbanization, population ageing
- Behavioral Risk Factors - unhealthy diet, physical inactivity, tobacco use, alcohol use
- Metabolic Risk Factors - raised bp, raised blood glucose, abnormal blood lipids, obesity or overweight
- Non Communicable Diseases
Poverty and NCDs
POVERTY
-economic deprivation
-low education
-unemployement
NCDs
-higher prevalence
-lack of care
-more severe disease
ECONOMIC IMPACT
-increased health expenditure
-loss of job
-reduced productivity
CDs and NCDs
-Viral infections and cancers
(HBV and liver CA; HPV and cervical CA)
-Infectious diarrhea and/or intesinal parasitism and malnutrition
-Pneumonia and chronic lung dse
-TB and DM
-HIV/AIDS and Kaposi sarcoma
Prevention and Control of NCDs
1. PREVENTION
-reduce the level of exposure to RF
2. MANAGEMENT
-strengthen healthcare for people with NCDs
3. SURVEILLANCE
-map out the epidemic of NCDs and RF
Global Action Plan Vision a world free of the AVOIDABLE BURDEN of NCDs
prevention and control of NCD in INFANCY
-exclusive breastfeeding up to 6 months
-nutritionally adequate and safe complimentary feeding starting from the age of 6 months with continued breastfeeding up to 2 yrs or beyond
prevention and control of NCD in CHILDHOOL/ADOLESCENCE
-improve life skills education
-promote physical activity
-safe and healthy foods in school
-restrict marketing of and access to food products high in sodium/sugar and unhealthy fats
-institute tobacco and alcohol controls
prevention and control of NCD in ADULT
-improve maternal condition
-implement tobacco prevention and cessation programs
-improve food availability and accessibility
-encourage physical activity
-provide access to effective prevention and care of risks and diseases
NCD Surveillance
- Outcomes
- Exposures
- Health System response
PUBLIC HEALTH SURVEILLANCE
etymology French
"sur" (over) + "veiller" (to watch)
Systematic ongoing collection, collation, analysis, interpretation, and dissemination of health data.
Purpose of public health surveillance
Public health surveillance provides and interprets data to facilitate the prevention and control of disease
Characteristics of Well-Conducted Surveillance
1. Acceptability
-the willingness of individual persons and organizations to participate in surveillance
2. Flexibility
-the ability of the method used for surveillance to accommodate changes in operating conditions or information needs with little additional cost in time, personnel, or funds
3. Quality
-the completeness and validity of the data used for surveillance
4. Representativeness
-the extent to which the findings of surveillance accurately portray the incidence of a health event among a population by person, place, or time
5. Stability
-the reliability of the methods for obtaining and managing surveillance data and to the availability of those data
6.Timeliness
-the availability of data rapidly enough for public health authorities to take appropriate action
7. Validity
-whether surveillance data are measuring what they are intended to measure.
8. Simplicity
-the ease of operation of surveillance as a whole and of each of its components
Essential Activities of public health surveillance
1. Identifying Health Problems for Surveillance
2. Identifying or Collecting Data for Surveillance
3. Analyzing and Interpreting Data
4. Disseminating Data and Interpretations
5. Evaluating and Improving Surveillance
Criteria for selecting and prioritizing health problems for surveillance (Public health importance of the problem)
- incidence, prevalence,
- severity, sequela, disabilities,
- mortality caused by the problem,
- socioeconomic impact,
- communicability,
- potential for an outbreak,
- public perception and concern, and
- international requirements.
Criteria for selecting and prioritizing health problems for surveillance
- Ability to prevent, control, or treat the health problem
- preventability
- control measures
- treatment
- Capacity of health system to implement control measures for the health problem
- speed of response,
- economics,
- resource requirements
- availability of resources,
Case Definition (Health Surveillance)
-an operational definition of the health problem for surveillance is necessary for the health problem to be accurately and reliably recognized and counted.
-might differ from:
a. clinical criteria
b. case definition used in outbreak investigation
Syndromic Surveillance
-use less specific criteria
- consists of a constellation of s/sx, shief complaints, or rather characeristics of the disease, rather than specific clinical or laboratory disgnostic criteria
*GOAL: earlier indication of unusual increase in illnesses to facilitate EARLY INTERVENTION
Sentinel Surveillance
- Relies on a prearranged sample of health-care providers who agree to report all cases of certain conditions. These sentinel providers are clinics, hospitals, or physicians who are likely to observe cases of the condition of interest.
- Sample used in sentinel surveillance might not be representative of the entire population
- Reporting is probably consistent over time because the sample is stable and the participants are committed to providing high-quality data
Active Surveillance Public health surveillance in which the health agency solicits reports.
Passive Surveillance Reporting of disease by physicians, labs, hospitals (cancer registry, birth registry, etc)
Typical Sources of Data
- Individual persons
- Health-care providers, facilities, and records
-Physician offices
-Hospitals (Outpatient departments, Emergency departments, Inpatient settings)
-Laboratories
- Environmental conditions
-Air
-Water
-Animal vectors
- Administrative actions
- Financial transactions
-Sales of goods and services
-Taxation
- Legal actions
- Laws and regulations
methods are used to collect the majority of health-related data
- environmental monitoring
- surveys
- notifications
- registries
- re-analysis of secondary data
Basic Considerations in Analyzing and Interpreting Data
- Different data types imply different type of analysis
-Descriptive methods are usually appropriate
- Data must be compared over time or across areas
-Selection of Data for comparison
Analysis by TIME
PURPOSE: to characterize trends and detect changes in disease incidence.
METHODS:
-comparison of the number of case reports received for the current week with the number received in the preceding weeks
-comparison of the number of cases during the current period to the number reported during the same period for the last 2-10 years
-Analysis of long-term time trends, also known as secular trends, usually involves graphing occurrence of disease by year.
Analysis by PLACE
- Rates are often calculated by adjusting for differences in the population size
-usually displayed in a table or a map
-choloropleth maps
-other sophisticated applications following the advent of geographic information systems
Alert threshold
- Refers to the level of occurrence of disease that serves as an EARLY WARNING FOR IMPENDING EPIDEMICS
- Computation:
Weekly (o monthly) ave of no cases in the past 3-5 yrs + 1 SD
Epidemic threshold
- Refers to the level of occurrence of disease above which an URGENT RESPONSE IS REQUIRED
- Computation:
Weekly (o monthly) ave of no cases in the past 3-5 yrs + 2 SD
Analysis by TIME&PLACE
- As a practical matter, disease occurrence is often analyzed by time and place simultaneously.
-analysis by time and place can be organized and presented in:
a. tables
b. series of maps highlighting different periods or populations
Analyze by PERSON
>most common person characteristics are :
-age (mutually-exclusive and all-inclusive)
-sex
-race and ethnicity (less consistent)
>Person variables useful in analysis:
-school or workplace
-recent hospitalization
-risk factors for specific diseases
Interpreting results of analyses
- Scenario
- Increase in incidence of disease
- variation in the pattern of disease
- Response
- Further investigation
- Emphasis on prevention and control
When is further cases investigation warranted?
-a single case of an illness of public health importance
-suspicion of a common source of infection for two or more cases is often sufficient reason for initiating an investigation
-Suspicion might also be aroused from finding that patients have something in common
What amount of increase or variation is required for action?
-Priorities
-capabilities and resources of LHD
-public, political or media attention or pressure
Common causes of such artifactual changes are:
-Changes in local reporting procedures or policies
-Changes in case definition
-Increased health-seeking behavior
-Increase in diagnosis.
-increased in population size
-Increased physician awareness of the condition, or a new physician is in town.
-Increase in reporting
-New laboratory test or diagnostic procedure.
-Outbreak of similar disease, misdiagnosed as disease of interest.
-Laboratory error.
-Batch reporting
-duplicate reporting
Disseminating Data and Interpretations
-the timely, regular dissemination of basic data and their interpretations is a critical component of surveillance.
-provided reports or other data
-persons, agencies or institutions who use them for planning or managing control programs, administrative purposes, or other health-related decision-making.
Evaluating and Improving Surveillance
(1) identifies elements of surveillance that should be enhanced to improve its attributes,
(2) assesses how surveillance findings affect control efforts, and
(3) improves the quality of data and interpretations provided by surveillance.
Philippine Integrated Disease Surveillance and Response (PIDSR)
MOTIVATION:
-Inefficiencies, redundancies and duplication of efforts from distinct resource requirements and processes of disjointed surveillance systems
-need to comply with the 2005 IHR
Surveillance Systems under PIDSR
-Notifiable Disease Reporting System (NDRS)
-National Epidemic Sentinel Surveillance System (NESS)
-Expanded Program on Immunzation Surveillance System (EPI)
-HIV/AIDS Registry
Approaches of PIDSR
-Facillity and community based approaches (DRUs)
-case based data collection(for every case)
Flow of notification for immediately notifiable diseases
- Community
- BHS
- RHU
- CHO
- PESU/CESU
- RESU
- NEC
Notifiable events
- Acute Flaccid Paralysis
- AEFI
- anthrax
- human avian influenza
- measles
- meningococcal dse
- neonatal tetanus
- paralytic shellfish poisoning
- rabies
- SARS
SCREENING
Presumptive identification of an unrecognized disease or defect by the application of tests, examinations or other procedures than can be applied rapidly.
Characteristics of a disease appropriate for screening
1. Serious and severe
2. Effective treatment at earlier stage
3. Detectable in preclinical phase
4. Long and prevalent preclinical phase
Characteristics of a screening test
- economical
- convenient
- free of risk/discomfort
- acceptable to large no. of individuals
- highly valid and reliable
Validity of a test
Ability to distinguish between who has a disease and who does not
Sensitivity
-Ability to correctly identify those who HAVE the disease
-probability that a person will test positive given that s/he has the dse
-proportion of diseased indiv. who will test POSITIVE
TP / (TP + FN)
Specificity
-Ability to correctly identify those who DONT HAVE the disease
-probability that a person will test negative given that s/he has the dse free
-proportion of diseased indiv. who will test NEGATIVE
TN / (TN + FP)
Decreased cutoff point *more POSITIVE cases*
Sensitivity increases
Specificity decreases
FP increases
Increased cutoff point *more NEGATIVE cases*
Specificity increases
Sensitivity decreases
FN increases
False Negatives
Missing out on a disease that has very serious, even fatal prognosis
False Positives
-Burden on the healthcare system
-anxiety of being told a (+) test result
-stigma of having been labeles (+)
Predictive Value
Ability of a test/tool to predict the presence or absence of a trat from test results
Positive Predictive Value Probability that a positive test is correct
Increases with increased prevalence
TP / (TP + FP)
Negative Predictive Value the probability of being free of a disease if the results are negative"
TN/(TN+FN)
PV and Prevalence
-PV not fixed on characteristics of a test
-for rare dse, dse prevalence is the main determinant of PV
Precision
Ability of a test/tool to give consistent results when the test is performed more than once on the same indiv under tha same conditions
-aka reliability, reporoducibility or repeatability
Potential Systematic Error in Screening
- lead time bias - Early detection of disease is confused with increased survival
- length bias - you will detect more slowly progressive disease and less rapidly progressive disease
- volunteer bias - Volunteers (healthy people) who participate may differ from those who did not volunteer (sick people) and vice versa
Types of Screening
- Mass screening - Screening applied to entire populations
- Targeted screening - Applied to high risk groups
- Opportunistic screening -Case finding; aimed at patients who consult a health practitioner for some health purpose
- Multiphasic screening - use of several screening tests to detect several conditions at the same time
Multiple Screening Test
maybe done sequentially or simultaneously
Sequential Testing -Those who tested (+) in the first test will subjected to the second test
-Increases overall specificity
Simultaneous Testing -Participants are subjected to two or more tests at the same time
-increases overall sensitivity
FORMULA
Net Sn (sequential) -subject is dse (+) when test (+) in BOTH tests
SnA x SnB
Net Sp (sequential) - subj is dse (-) when test (-) in EITHER test
(SpA+SpB)-(SpAxSpB)
Net Sn (simultaneous) - subj is dse (+) when test (+) in EITHER test
(SnA+SnB)-(SnAxSnB)
Net Sp (simultaneous) -subject is dse (-) when test (-) in BOTH tests
SpA x SpB
PREVENTION AND CONTROL
Actions aimed at ERADICATING, ELIMINATING or MINIMIZING the IMPACT of disease and disability, or if none of these are feasible, RETARDING THE PROGRESS of disease and disability
Primordial Prevention
Stage of dse:
-underlying economic. social and environmental conditions leading to causation
Aim:
-establish and maintain conditions that minimize hazards to health
Interventions:
- mass education
- indiv education
- national policies and programs
Primary Prevention
Stage of dse: predisease; susceptible; exposed
Aim: reduce dse incidence
Goal:
-prevent dse from occurring
Interventions:
-health promotion
-specific protection (immunization)
Health Promotion
Process of enabling people to increase control over, and to improve their health. Moves beyond a focus on individual behavior towards a wide range of social and environmental interventions
-health education
-environmental modification
-nutritional interventions
-lifestyle and behavior changes
Specific Protection:
- immunization
- chemoprophylaxis
- use of specific nutrients
- PPEs
- food and drug safety
Secondary Promotion
Stage of dse: latent dse; early stage of dse; sublinical stage; asymptomatic
Aim: reduce prevalence of dse by shortening it duration
Goal:
-delay emergence of dse
-early detection
Interventions:
-screening
Tertiary Prevention
Stage of dse: late or advanced stage; symptomatic
Aim: reduce complications or disability
Goal:
-prevent or minimize progression of the dse or its sequelae
Interventions:
-disability limitations for early symptomatic
-rehabilition for late symptomatic
Control
Ongoing operations or progemas aimed at reducing incidence and/or prevalence or eliminating such conditions. Focus on primary and secondary preventions.
Control of Infectious Diseases (4Cs)
Case (dx,isolate,tx)
Contacts (quarantine)
Carriers (tx)
Community (certain area w/ dse)
Extinction total annhilation of the dse agent
Important precursor of eradication elimination of a dse in a global level
Determinants of prevention
-knowledge of causation
-dynamics of tranmission
-indentification of risk factors and risk groups
-availability of prophylactic or screening and treatment measures
-organization for applying these measure to appropriate persons or groups
-continuous evaluation and development of procedures applied
Preventable causes of diseases
-biologic and behavioral factor
-environmental factor
-immunologic factor
-nutritional factor
-genetic factor
-services and social factor
