BioEpi Prefinals 1 PDF

BIO-EPI BIOEPI PREFINALS 1 - E.g., infectious diseases, side effects of vaccines, elevated lead levels, EPIDEMIOLOGIC SURVEILLANCE AND pneumonia-related deaths EPIDEMIC OUTBREAK INV...

BIO-EPI BIOEPI PREFINALS 1 - E.g., infectious diseases, side effects of vaccines, elevated lead levels, EPIDEMIOLOGIC SURVEILLANCE AND pneumonia-related deaths EPIDEMIC OUTBREAK INVESTIGATION Requires clear objectives for each surveillance item I. SURVEILLANCE OF DISEASE - E.g., surveillance of an infectious disease to determine whether a A. Responsibility of Surveillance vaccine program is effective, the search for possible side effects of new vaccines Surveillance - entire process of The case definition usually is based collecting, analyzing, interpreting, and on clinical findings, laboratory results, reporting data on the incidence of and epidemiologic data on the time, death, diseases, and injuries place, and characteristics of affected Considered as the foundation of persons disease control efforts The following should be known in advance Centers for Disease Control and Prevention - Intensity of the planned surveillance (CDC) (active vs. passive) - Duration of the surveillance (ongoing Federal agency responsible for the vs. time-limited) surveillance of most types of acute - Type of analysis needed diseases and the investigation of outbreaks C. Methods and Functions of Disease Conducts surveillance if requested by Surveillance a state or if an outbreak has the potential to affect more than one state Passive Surveillance - physicians, Data are passed from local and state clinics, laboratories, and hospitals that governments to the CDC are required to report disease are given the appropriate forms and Federal gov't has jurisdiction over matters instructions concerning interstate commerce, including - Expected to record all cases of interstate implications (outbreaks originated reportable disease that come to their in one state and spread to other states). State attention gov't has jurisdiction over intrastate Active Surveillance - requires implications (outbreaks confined in one state periodic telephone calls, electronic only). contact or personal visits to the reporting individuals and institutions B. Creating a Surveillance System to obtain the required data - More labor intensive and costly = Requires clear objectives regarding seldom done on a routine basis the diseases or conditions to be covered BIO-EPI Percentage of patients with reportable detection, disease reporting, or both, as is diseases that are actually reported to public frequently the case when an apparent health authorities varies considerably. outbreak of a disease is reported. Sometimes a change in medical care practice uncovers a previously invisible disease Seasonal Variation- Many infectious diseases surveillance issue. Sometimes without show a strong seasonal variation, with significant support and funding from the periods of highest incidence usually government, surveillance systems are difficult depending on the route of spread. to establish. Respiratory route- higher incidence in the 1.Establishment of Baseline Data winter and early spring in the Northern Hemisphere Usual rates and patterns of diseases can be known only if there is a regular Influenza, colds, measles, varicella reporting and surveillance system (chickenpox) Epidemiologists study the patterns of diseases by the time and geographic Insect/Arthropod vectors - summer or early location of cases and the autumn characteristics of the persons involved Lyme disease Continued surveillance detects deviations from the usual pattern of Fecal-oral route - most common in the data, which can prompt them to summer because of the ability of organisms explore whether an epidemic is to multiply faster during the warm weather occurring or other factors Gastrointestinal diseases 2. Evaluation of Time Trends Epidemiologic year - runs from the month of Secular (Long-Term) Trends lowest incidence in a one year to the same month in the next year 3. Identification and Documentation of Outbreaks Epidemic - aka disease outbreak occurrence of disease at an unusual frequency k E.g., To determine when and where The first question to ask is whether the trend influenza and pneumonia outbreaks can be explained by changes in disease occur, the CDC uses a seasonally adjusted expected percentage of BIO-EPI influenza and pneumonia deaths in Shows the impact of the two types of polio the United States and a number vaccine (inactivated and oral vaccine) called epidemic threshold to compare with the reported percentage. Shows that after the inactivated vaccine was introduced in 1955, the rates of paralytic disease declined quickly The public tended to think the problem had gone away and many SURVEILLANCE FOR BIOTERRORISM parents became less concerned about immunizing newborns Special surveillance techniques are Recurrent polio spike occurred in being developed to enable rapid 1958 and 1959 detection of major increases in the Declined again by 1960 after most likely biologic agents obtaining new oral vaccine Syndromic surveillance THE FAILURE OF A VACCINE TO PRODUCE SATISFACTORY IMMUNITY CAN BE Technique developed for more rapid DETECTED BY ONE OF THE FOLLOWING: detection of epidemics and possible bioterrorism Goal: characterize "syndromes" that A lack of change in disease rates would be consistent with agents of An increase in disease rates after an particular concern and to prime the initial decrease system to report any such syndromes An increase in disease rates in a quickly recently vaccinated group Provide an early warning of bioterrorism problem 5. Setting of Disease Control Priorities 4. Evaluation of Public Health and Disease Data on the patterns of diseases for Interventions the current time and recent past can help governmental and voluntary agencies establish priorities for disease control efforts. BIO-EPI The severity of the disease is a critical use of crack and with their lack of feature, which usually can be prenatal care. established by good surveillance. Il. INVESTIGATION OF EPIDEMICS 6. Study of Changing Patterns of Disease A. Nature of Epidemics By studying the patterns of occurrence of a particular disease Epidemic = unusual occurrence of over time in populations and disease; "upon the population" subpopulations, epidemiologists can If a disease has been eradicated from better understand the changing a particular region or if a disease is patterns of the disease. approaching elimination from an area and has the potential for spread, the report of even ONE CASE in the geographic region might be considered unexpected and become a cause for concern Endemic- Disease in a population occurs regularly and at a more or less constant level "Within the population" Epizootic- Disease outbreak in an animal population "Upon the animals" Data derived from the surveillance of Enzootic- Disease deeply entrenched in an syphilis cases in New York City during animal population but not changing much the 1980s, when crack cocaine came into common use, proved valuable in "Within the animals" suggesting the source of changing patterns of acquired and congenital syphilis. Attack Rate Reported number of cases of primary and secondary syphilis among Investigators of acute disease women increased beginning in 1987. outbreaks ordinarily use a measure of Both this trend and the concurrent disease frequency called the attack increase in congenital syphilis were rate, particularly when the period of strongly associated with the women's exposure is short (less than one year. BIO-EPI Proportion of exposed persons that - When were the affected persons becomes ill exposed? What was the incubation period? - In addition to primary cases, were there secondary cases? Common source exposure B. Procedures for Investigating an Epidemic - people come in contact with the same Establish the Diagnosis source (contam. water or food) Establish Epidemiologic Case - epidemic curve has a sudden onset, a Definition peak, and a rapid decline - List of specific criteria used to decide whether or not a person has the Person-to-person spread disease of concern - Established consistent criteria that - epidemic curve has a prolonged, enable epidemiologic investigations irregular pattern aka PROPAGATED to proceed before definitive OUTBREAK diagnoses are available - Important if the disease is unknown Index case Is an Epidemic Occurring? - Even if proven, cases must occur in first person affected in the situation; sufficient numbers to constitute an introduced the organism into the epidemic population Characterize Epidemic by Time, Place, and Person Epidemic time curve from an outbreak of gastrointestinal disease caused bycommon CHARACTERIZE EPIDEMIC BY TIME, source exposure to Shigella boydi. PLACE, AND PERSON Spaghetti was contaminated by a food TIME handler. Time scale is 12-hour periods. Note Epidemic time curve - Time dimension of the outbreak - Graph with time on x-axis and number of new cases on the y-axis - Provides clues about what is happening in an outbreak - What was the type of exposure? - What was the probable route of spread? BIO-EPI the rapid increase and rapid decrease. returned home, they infected others with shigellosis. METHOD 1 Taking the shortest and longest known incubation period for the causative organism and calculating backward in time from the first and last cases E.g., the incubation period for Shigella organisms is usually 1 to 3 days (24 to 72 hours), but it may range from 12 to 96 hours METHOD 2 ——————————————————————— Involves taking the average Sometimes an epidemic has more than one incubation period and measuring peak, either because of multiple common backward from the epidemic peak source exposures or because of secondary cases. CHARACTERIZE EPIDEMIC BY TIME, PLACE, AND PERSON PLACE Involves defining the location of all cases Spot Map - shows where each affected person lives, works, or attends school, is helpful in solving an epidemic puzzle. Use is limited in outbreak investigations kShows only the number of cases and not the number of persons in the area Figure 3-14 shows the epidemic time curve for an outbreak of shigellosis among students Epidemiologists prefer to show the who attended sa summer camp in the incidence rates by location (i.e.Hospital ward, eastern United States. The campers who Work Area or Classroom, or by block or drank contaminated water on the trip were section of a city). infected with Shigella organisms. After they BIO-EPI John Snow - prepared the most famous spot - Travel and contacts with other map in 1855. affected persons. Spot Map of Cholera Deaths in the Soho District of London, 1854, The deaths centered on the intersection of Borad and Lexington streets. ——————————————————————— Incidence of Measles in Residents of Cuyahoga County, Ohio, by Age Group, from October 1973 to February 1974. CHARACTERIZE EPIDEMIC BY TIME, PLACE, AND PERSON PERSON Knowing the characteristics of persons affected by an outbreak may help clarify the problem and its cause. Important Characteristics include: ——————————————————————— - Age - Gender Comparison - Race - Ethnicity The measles in Navajo Nation tended to - Religion occur in very young children - Source of water, milk, food - Immunization Status Outbreak was caused by lack of - Type of Work or Schooling immunization of preschool-age children BIO-EPI Very young children in Cuyahoga County - Occurs when contaminated water or were almost exempt from measles food is consumed by many people in the same time period Younger children had been Propagated Pattern immunized - Infection disseminates itself by Outbreak resulted from the failure of spreading directly from person to measles vaccine to produce person over an extended period long-lasting immunity. Mixed Pattern - Persons acquire a disease through a common source and spread it to family members or others (secondary cases) by personal contact Mode of Transmission may be: Respiratory Fecal-Oral Vector-borne Skin to Skin Through exchange of Serum or other Body Fluids Contact with Fomites B. Procedures for Investigating an Epidemic Fomites - objects that can passively carry organisms from one person to Develop hypotheses regarding source, another, such as soiled sheets or door patterns of spread, and mode of transmission knobs Source of Infection -the person (index case) TEST HYPOTHESIS or vehicle (food, water) that initially brought the infection into the affected community. - Laboratory Studies may include one or more of the following: Pattern of Spread - pattern by which Cultures from patients, and if infection can be carried from the source to appropriate, from possible vehicles the individuals infected (e.g., food or water) Stool examinations for ova and Common-Source Pattern parasites Propagated Pattern Serum tests for antibodies to the Mixed Pattern organism suspected of cauing the disease Pattern of Spread Tests for non-microbiologic agents, such as toxins or drugs Common-Source Pattern BIO-EPI Test Hypothesis Initiate Control Measures - Conducting Case Control Studies - common, efficient way After noting an outbreak, it is usually accompanied by a general outcry that Example: Food Outbreak of Disease something must be done immediately. Control measures - initiated in such a 1. Investigator assembles the cases way as not to interfere with the (persons who have the disease) and investigation of the outbreak controls (sample of persons who ate at the same place at the suspected 4 Common Types of Interventions time but do not have the disease) 2. Look for possible risk factors (e.g. Sanitation food items eaten) Prophylaxis 3. Compare the food eaten by controls Diagnosis and Treatment and food eaten by cases, those that Control of Disease vectors were eaten by both controls and cases were eliminated as possible TYPES OF INTERVENTIONS source of infection 4. Food item that is unique to cases is 1. Sanitation the most likely risk factor a. Modification of the environment i. Removing pathogenic agent from Example: Noninfectious Disease source of infection (Adenocarcinoma of the Vagina, 1971) ii. Removing the human source of infection (quarantine) 1. 8 women treated at one hospital ill. Prevent contact with the source, by 2. 32 controls (4 women per 8 of the cleaning environment or removing cases) susceptible people (evacuation) 3. Define the risk factors 2. Prophylaxis 4. Results showed that 7 of the 8 cancer a. Putting a barrier to the infection patients had been exposed to i. Vaccine (e.g. Antimalarial Drugs, Diethylstilbestrol (DES) in utero. Hyperimmune Globulin against Hep a. Mothers of the cases had been A) given DES during Ist trimester to 3. Diagnosis and Treatment prevent miscarriage a. Performed for those infected (B, b. None of the 32 controls was the Syphilis, Meningococcal Meningitis) to offspring of mothers given DES during prevent spread of disease to others pregnancy 4. Control of Disease Vectors a. Including mosquitoes (malaria, dengue, yellow fever) and Ixodes ticks (Lyme disease) -- use of mosquito nets BIO-EPI Important Aspect: Surveillance- Used for setting disease control policy Written and Oral Communication to: Investigation of Disease Outbreaks- Is the Appropriate Authorities primary function of public health agencies, Appropriate Health Professionals but the practicing physician makes important Public contributions in detecting and reporting acute outbreaks. The Communication: IL. INVESTIGATION OF EPIDEMICS 1. Enables other agencies to assist in disease control Standard Approach to Investigation of 2. Contributes to the professional fund Disease Outbreaks of knowledge about teh causes and control of outbreaks Developed in 20th Century Involves: 3. Adds to the available information on prevention Making a diagnosis Establishing a case definition B. Example of Preparedness and Response Determining whether there is a to a Global Health Threat definite outbreak If outbreak is occurring: Characterize time, place, and person Development and testing of hypotheses, pattern of spread, and mode of transmission Surveillance of Disease Activity Hypotheses are tested using laboratory data or research methods - is the foundation of public health depending on the hypotheses control of disease. Control measures and follow-up surveilance initiated as soon as is May be: Active or Passive practical. Functions include: Determining baseline rates of disease Detecting outbreaks Evaluating Control Measures Ill. SUMMARY