101 Questions
What is the primary purpose of disease surveillance?
To promote and safeguard public health
What is the foundation of disease control efforts?
Surveillance
What is required for the development of a surveillance system?
Clear objectives regarding the diseases or conditions to be covered
What do epidemiologists study to understand patterns of diseases?
The time and geographic location of cases and the characteristics of persons involved
What may be responsible for the observed changes in disease patterns?
Changes in disease detection or reporting practices
What does a long-term increase in a disease in one region suggest?
A more widespread problem
Why do infectious diseases that are spread by the respiratory route have a higher incidence in the winter and early spring?
Because people spend more time indoors, where the air changes slowly
What is the effect of the introduction of varicella vaccine on the seasonal pattern of varicella?
It has eliminated the seasonal pattern
What is the purpose of incorporating seasonal variation into calculations?
To determine the usual number of cases or rates of disease
What is the significance of a long-term trend in disease?
It is usually of greater significance than an outbreak or epidemic
When are most diseases spread by insect or arthropod vectors typically acquired?
Late spring or summer
What is the purpose of using an 'epidemiologic year'?
To put the high-incidence months near the center of a graph
Why does recreational drowning occur more frequently on weekends?
Because more people engage in water recreation on weekends
What is an epidemic?
An unusual frequency of disease
How does the CDC determine when and where influenza and pneumonia outbreaks occur?
By comparing reported deaths to a seasonally adjusted expected percentage
What is the main concern of surveillance for bioterrorism?
Rapid detection of a problem
What makes detection of bioterrorism more difficult?
If the disease is scattered over a wide geographic area
What is the purpose of special surveillance techniques in bioterrorism?
To enable rapid detection of major increases in the most likely biologic agents
What is the primary objective of surveillance in determining the effectiveness of a vaccine program?
To determine whether a vaccine program is effective
What is typically used to define a case of a reportable disease or condition?
Clinical findings, laboratory results, and epidemiologic data
What is the main difference between active and passive surveillance?
Active surveillance requires periodic telephone calls, while passive surveillance does not
Why is it important to have clear objectives for each surveillance item?
To ensure that the surveillance system is focused and productive
Why is it important to evaluate the full surveillance system continually?
To ensure that the system is effective in detecting disease outbreaks
What is an example of a change in medical care practice that uncovered a previously invisible disease surveillance issue?
A hospital began reporting many cases of pharyngeal gonorrhea in young children
Why are surveillance systems for non-infectious diseases and conditions often difficult to establish?
Lack of significant support and funding from governments
What is a limitation of using death certificates to monitor fatal diseases?
Diagnoses are often inaccurate
What is the main goal of syndromic surveillance?
To characterize 'syndromes' consistent with agents of particular concern
What is shown in Figure 3-9?
The impact of the two types of polio vaccines on reported incident cases of poliomyelitis
Why did the rates of paralytic disease decline quickly after the introduction of the inactivated vaccine in 1955?
Because of the rapid adoption of the inactivated vaccine
What can indicate the failure of a vaccine?
A lack of change in disease rates or an increase in disease rates after an initial decrease
What was the result of postmarketing surveillance of measles vaccines and vaccination schedules?
The detection of the failure of the initial measles vaccines to provide long-lasting protection
What can be inferred from studying the patterns of occurrence of a particular disease over time?
The changing patterns of the disease
Why was there a greater effort to detect tuberculosis in people with AIDS?
Due to the increasing impact of the AIDS epidemic
Why is data on disease patterns important for setting disease control priorities?
Because it helps establish priorities for disease control efforts
What does the oral polio vaccine provide in addition to individual immunity?
Herd immunity
What is the definition of an epidemic?
The unusual occurrence of a disease
What would be considered an epidemic in a region where a disease has been eradicated?
A single case of the disease
What term is used to describe a disease that is deeply entrenched in an animal population?
Enzootic
What is the attack rate used to measure?
The proportion of exposed persons that becomes ill
What is the purpose of the constant multiplier in the attack rate equation?
To express the rate as a percentage
What is the term used to describe a disease that occurs regularly and at a more or less constant level in a population?
Endemic
Why would a single case of a disease be considered an epidemic in a region where it has been eliminated?
Because it has the potential for spread
What is the difference between an epidemic and an endemic disease?
An epidemic is an unusual occurrence, while an endemic disease is a regular occurrence
What determines the data needed to classify persons as affected or unaffected?
Case definition
What type of graph is used to describe the time dimension of an outbreak?
Epidemic time curve
What type of exposure would result in an epidemic time curve with a sudden onset, peak, and rapid decline?
Common source exposure
What is the term for the case that introduced the organism into the population?
Index case
What type of outbreak would result in an epidemic time curve with a prolonged, irregular pattern?
Person-to-person spread
What can cause an epidemic time curve to have multiple peaks?
All of the above
What is the term for the period of time between exposure to a disease and the onset of symptoms?
Incubation period
What is the purpose of creating an epidemic time curve?
To understand the outbreak and answer important questions
What type of transmission can result in an epidemic time curve similar to a common source exposure?
Respiratory transmission
What is the primary goal of investigating an epidemic?
To discover and correct recent changes to restore balance
What is the first step in investigating a disease outbreak?
Establish the diagnosis
What is the purpose of the epidemiologic case definition?
To decide whether or not a person has the disease of concern
Why is it important to establish a case definition early in an outbreak investigation?
To establish consistent criteria for epidemiologic investigations
What is necessary to determine if an epidemic is occurring?
Cases occurring in sufficient numbers to constitute an epidemic
What is characterized by time, place, and person in an outbreak investigation?
The epidemic
What is the significance of knowing the usual number of cases in ongoing surveillance?
It helps to determine if an epidemic is occurring
Why is it important to investigate an outbreak?
To discover and correct recent changes to restore balance
What can be a result of a correct diagnosis during an outbreak investigation?
The outbreak is stopped
What is a limitation of establishing a case definition?
There are always some false positives and false negatives
What is the primary purpose of using the epidemic time curve in an outbreak investigation?
To determine the probable time of exposure
What is the typical range of incubation period for Shigella organisms?
12 to 96 hours
What can be inferred from the geographic clustering of cases in an outbreak investigation?
Important clues about the source of the outbreak
Why do epidemiologists prefer to show incidence rates by location instead of using spot maps?
Because spot maps do not provide information on the denominator
What is the limitation of using spot maps in outbreak investigations?
They only show the numerator and not the denominator
What was the probable cause of the outbreak of respiratory fungal infection in the Arkansas school?
Coal dust contaminated with Histoplasma capsulatum
What can be inferred from comparing trends in incidence rates in different regions?
The spread of a disease from one region to another
What can help epidemiologists decide whether a cluster of disease cases represents an environmental problem?
The types of cancer in the cluster
What is the next step after identifying a cluster of disease cases?
Begin observing the situation prospectively
What characteristic of affected individuals may help clarify the cause of an outbreak?
All of the above
What may indicate a true environmental problem in an area?
A cluster of disease cases with a single type or a small number of related types of cancer
What is a difficulty in distinguishing 'chance' clusters from 'real' clusters of disease?
The theory of random sampling
What can be a problem in neighborhoods or small areas?
Clusters of disease cases
What is the primary difference between a common-source outbreak and a propagated outbreak?
Common-source outbreaks have a single point of exposure, while propagated outbreaks spread from person to person
What is the purpose of conducting laboratory studies in epidemiology?
To test epidemiologic hypotheses
What is an example of a common-source exposure?
Eating contaminated spaghetti
What is the mode of transmission of an epidemic disease that involves contact with contaminated objects?
Through fomites
What is the purpose of a case-control study in epidemiology?
To identify risk factors
What is the significance of the second dose of measles vaccine in preventing outbreaks?
It prevents outbreaks of measles
What is the purpose of a serum test in laboratory studies?
To detect antibodies to the suspected organism
What is an example of a propagated pattern of spread?
Shaking hands with someone who is sick
What is the term used to describe a disease that occurs regularly and at a more or less constant level in a population?
Endemic
What is the purpose of testing hypotheses in epidemiology?
To understand the pattern of spread
What is the primary purpose of initiating control measures during an outbreak?
To prevent further transmission of the disease
What is an example of a sanitation effort to control an outbreak?
Removing the pathogenic agent from the source of infection
Why is it important to communicate findings to the appropriate authorities, health professionals, and the public during an outbreak?
To enable other agencies to assist in disease control and contribute to the professional fund of knowledge
What is the purpose of initiating specific follow-up surveillance after an outbreak?
To evaluate the effect of the control measures
What is an example of a prophylaxis measure to control an outbreak?
Putting a barrier to the infection, such as a vaccine
What is the purpose of modification of the environment in sanitation efforts?
To prevent contact with the source of infection
What was the probable source of the outbreak of acute gastrointestinal illness at the college?
A food handler who worked while ill
What was the symptom that most students experienced during the outbreak?
Nausea and vomiting
What is the primary objective of diagnosis and treatment during an outbreak?
To prevent further transmission of the disease
Why is it important to have active surveillance after an outbreak?
It is more reliable than passive surveillance
What was the purpose of developing a case definition for the investigation?
To define a case for the purpose of the investigation
What is the primary function of public health agencies in investigating disease outbreaks?
Detecting and reporting acute outbreaks
What is the significance of laboratory data in investigating disease outbreaks?
To test hypotheses regarding the source of infection
What is the purpose of follow-up surveillance after an outbreak?
To evaluate control measures
What is the main goal of surveillance in public health?
To set disease control policy
What is the role of the practicing physician in disease surveillance?
To detect acute outbreaks
Study Notes
Surveillance of Disease
- Surveillance is the entire process of collecting, analyzing, interpreting, and reporting data on the incidence of death, diseases, and injuries and the prevalence of certain conditions.
- The Centers for Disease Control and Prevention (CDC) is the federal agency responsible for the surveillance of most types of acute diseases in the United States.
Creating a Surveillance System
- A surveillance system requires clear objectives regarding the diseases or conditions to be covered.
- The objectives for each surveillance item should be clear, and the criteria for defining a case of a reportable disease or condition must be known.
- The intensity of the planned surveillance (active vs. passive) and duration of the surveillance (ongoing vs. time-limited) must be known in advance.
Methods and Functions of Disease Surveillance
- Surveillance may be either passive or active.
- Passive surveillance is when physicians, clinics, laboratories, and hospitals report disease cases, while active surveillance involves periodic telephone calls, electronic contact, or personal visits to obtain data.
- The percentage of patients with reportable diseases that are actually reported to public health authorities varies considerably.
Establishment of Baseline Data
- Usual (baseline) rates and patterns of diseases can be known only if there is a regular reporting and surveillance system.
- Epidemiologists study the patterns of diseases by the time and geographic location of cases and the characteristics of the persons involved.
Evaluation of Time Trends
- Secular (long-term) trends in disease are usually different from those of outbreaks or epidemics and often carry greater significance.
- Seasonal variation is a common pattern in infectious diseases, with periods of highest incidence usually depending on the route of spread.
Identification and Documentation of Outbreaks
- An epidemic, or disease outbreak, is the occurrence of disease at an unusual (or unexpected) frequency.
- To determine that the level of a disease is unusual, the usual rates of the disease must be known, and reliable surveillance must show that current rates are considerably elevated.
Surveillance for Bioterrorism
- Epidemiologists have worried about the use of biologic agents for military or terrorist purposes.
- Special surveillance techniques are being developed to enable rapid detection of major increases in the most likely biologic agents.
Evaluation of Public Health and Disease Interventions
- The introduction of major interventions intended to change patterns of disease in a population should be followed by surveillance to determine if the intended changes were achieved.
- Surveillance can help detect the failure of a vaccine to produce satisfactory immunity or the failure of people to use the vaccine.
Setting of Disease Control Priorities
- Data on the patterns of diseases for the current time and recent past can help governmental and voluntary agencies establish priorities for disease control efforts.
Study of Changing Patterns of Disease
- By studying the patterns of occurrence of a particular disease over time in populations and subpopulations, epidemiologists can better understand the changing patterns of the disease.
Investigation of Epidemics
- Definition of an epidemic: an unusual occurrence of a disease, derived from Greek roots meaning "upon the population"
- Can be a single case of a disease that has been eliminated or eradicated from a region
Terms for Disease Patterns in Animals
- Epizootic: a disease outbreak in an animal population
- Enzootic: a disease deeply entrenched in an animal population but not changing much
Attack Rate
- Measures disease frequency
- Calculated as: (Number of new cases / Number of persons exposed) x 100
- Expressed as a percentage
Procedures for Investigating an Epidemic
- Establish the diagnosis
- Establish an epidemiologic case definition
- Determine if an epidemic is occurring
- Characterize the epidemic by time, place, and person
Characterizing an Epidemic
- Time: use an epidemic time curve to show the number of new cases over time
- Place: create a spot map to show the location of cases
- Person: gather information on age, gender, race, ethnicity, religion, and other personal characteristics of affected individuals
Developing Hypotheses
- Identify the source of infection
- Determine the pattern of spread (common-source, propagated, or mixed)
- Identify the mode of transmission### Modes of Transmission
- Respiratory transmission
- Fecal-oral transmission
- Vector-borne transmission
- Skin-to-skin transmission
- Transmission through exchange of serum or other body fluids
- Transmission through contact with fomites (objects that can passively carry organisms)
Laboratory Studies
- Cultures from patients and possible vehicles (e.g., food, water)
- Stool examinations for ova and parasites
- Serum tests for antibodies to suspected organisms
- Tests for nonmicrobiologic agents (e.g., toxins, drugs)
Case-Control Studies
- Assemble cases (people with the disease) and controls (people without the disease)
- Question both groups about specific foods eaten before the outbreak
- Calculate the percentage of controls who consumed each food item and subtract from the percentage of cases who consumed it
- Identify the food item with the greatest difference in consumption percentage between cases and controls as the most likely risk factor
Control Measures
- Sanitation: modify the environment to remove the pathogenic agent
- Prophylaxis: use a barrier to infection (e.g., vaccine, immunization)
- Diagnosis and treatment: treat infected individuals to prevent spread
- Control of disease vectors (e.g., mosquitoes, ticks)
Follow-up Surveillance
- Evaluate the effect of control measures
- Detect subsequent outbreaks
- Active surveillance is more reliable than passive surveillance
Investigation of an Outbreak
- Define the case criteria
- Conduct interviews with affected people
- Analyze the epidemic time curve
- Identify possible risk factors (e.g., food handlers working while ill)
- Consider past knowledge from similar outbreaks and disease surveillance
- Make recommendations based on the investigation's findings
Surveillance of Disease Activity
- Surveillance is the foundation of public health control of disease and can be active or passive.
- The functions of surveillance include determining baseline rates of disease, detecting outbreaks, and evaluating control measures.
Investigation of Disease Outbreaks
- Investigation of disease outbreaks is a primary function of public health agencies.
- Practicing physicians contribute to detecting and reporting acute outbreaks.
- The standard approach to investigating disease outbreaks involves:
- Making a diagnosis
- Establishing a case definition
- Determining whether there is a definite outbreak
Characterizing Outbreaks
- If an outbreak is occurring, cases are characterized by:
- Time (using an epidemic time curve)
- Place (determining rates in people who live and work in different locations)
- Person (determining personal characteristics and patterns of people involved in the outbreak)
Developing and Testing Hypotheses
- Hypotheses are developed regarding:
- Source of infection
- Pattern of spread
- Mode of transmission
- Hypotheses are tested using:
- Laboratory data (e.g., cultures, paired sera, analysis for toxins)
- Research methods (e.g., case-control studies)
Control Measures and Follow-up
- Control measures and follow-up surveillance are initiated as soon as practical.
- This is done to prevent further transmission of the disease.
Learn about the process of disease surveillance, its importance, and how it promotes public health. Discover the role of Centers for Disease Control and Prevention (CDC) in the United States.
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