Describe these data by person place and time (i.e. descriptive epidemiology). For more information on descriptive epidemiology please refer to the Module 3 Home Page.

/in /by

Module 1 Background
INTRODUCTION TO EPIDEMIOLOGY: THE EPIDEMIOLOGIC APPROACH
Required Readings
Coggon D. Rose G. & Barker D.J.P. (2007) Epidemiology for the Uninitiated (4th edition). British Medical Journal. Retrieved May 22 2012 from http://www.bmj.com/about-bmj/resources-readers/publications/epidemiology-uninitiated
Centers for Disease Control and Prevention. PulseNet. Retrieved Retrieved May 22 2012 from http://www.cdc.gov/pulsenet/
Centers for Disease Control and Prevention Timeline for Reporting of E. coli Cases. Retrieved February 26 2011. http://www.cdc.gov/ecoli/reportingtimeline.htm
OMRAN A. (2005). The Epidemiologic Transition: A Theory of the Epidemiology of Population Change. Milbank Quarterly 83(4) 731-757. doi:10.1111/j.1468-0009.2005.00398.x. Retrieved Retrieved May 22 2012 from: http://onlinelibrary.wiley.com/doi/10.1111/j.1468-0009.2005.00398.x/pdf
Principles of Epidemiology. Retrieved Retrieved May 22 2012 from University of Illinois at Chicago Web site: http://www.uic.edu/sph/prepare/courses/ph490/resources/epilesson01.pdf
DNA Fingerprinting. Retrieved May 22 2012 from cphp.sph.unc.edu/focus/vol4/issue4/4-4LabTechniques_slides.ppt
Module 1 Multiple causation
INTRODUCTION TO EPIDEMIOLOGY: THE EPIDEMIOLOGIC APPROACH
Multiple causation refers to the prerequisite that more than one factor must be present for disease to develop in a host. When a factor must be present for a disease to occur it is called the agent of that disease. For example HIV virus is the agent of AIDS. Although an agent is necessary it is not sufficient to cause disease. Factors that may affect the development of disease can be classified into two groups:1) host factors and 2) environmental factors.
Host Factors
The state of the host is affected by genetic factors and past environmental exposures. These factors can affect the susceptibility of a host. For example sickle celltrait (a genetic factor) is associated with a decreased risk of malaria. Past environmental exposures that affect susceptibility include specificimmunity which is a state of altered responsiveness to a specific substance acquired through immunization or natural infection. Other environmental exposures be chemical in nature (e.g. cigarette smoking asbestos).
Environmental Factors
Environmental factors can be categorized as biological social or physical. Biological factors include the agent of the disease the place where the agent lives and multiplies (e.g.human beings animals soil) vectors that transmit disease (e.g. flies andmosquitoes) and antibiotics. Social factors include the technical level of medical care health codes controlling environmental hazards and social customs. For example the custom of serving chicken tataki (undercooked chicken) may expose an individual to infectious agents such as Salmonellaor Campylobacter. Physical factorsinclude heat light air water radiation gravity atmospheric pressure andchemical agents. When weather conditions cause masses of air pollution to be trapped for several days inhabitants can be exposed to noxious substancesthat can lead to chronic diseases.
Ecologic Models
Ecological models have been developed to illustrate the ways in which these interactions influence the occurrence of disease. Two commonly used models include the epidemiologic triangle and the web of causation.
The epidemiologic triangle consists of three components: host environment and agent. A change in any of the components will affect the equilibrium by increasing or decreasing the frequency of disease. For example individuals exposed to the common cold virus may not all become ill because of differences in nutrition or stress (host factors).
The web of causation is often used to explain conditions that have not been linked to specific agents. In this model more emphasis is placed on the multiplicity of interactions between the host and environment rather than the agent. According to this model conditions develop as a result of chains of causation in which each link represent a complex web of antecedents.
Module 1 Outbreak Detection
INTRODUCTION TO EPIDEMIOLOGY: THE EPIDEMIOLOGIC APPROACH
Escherichia coli O157:H7 was first identified as a human pathogen in 1982 in the United States of America following an outbreak of bloody diarrhea associated with contaminated hamburger meat. Sporadic infections and outbreaks have since been reported from many parts of the worldincluding North America Western Europe Australia Asia and Africa. Although other animals are capable of carrying and transmitting theinfection cattle are the primary reservoir for E. coli O157:H7. Implicated foods are typically those derived from cattle (e.g. beefhamburger raw milk); however the infection has also been transmitted through contact with infected persons contaminated water and other contaminated food products.
Infection with E. coli O157:H7 is diagnosed by detecting the bacterium in the stool. Most laboratories that culture stool do not routinely test for E. coli O157:H7 but require a special request from the health care provider. Only recently has E. coli O157:H7 infection become nationally notifiable in the U.S. Outside the U.S. reporting is limited to a few but increasing number of countries.
In the last week of June 1997 a certain state department of community health in the US noticed an increase in laboratory reports of E. coli O157:H7 infection. Fifty-two infections had been reported that month compared with 18 in June of 1996. In preliminary investigations no obvious epidemiologic linkages between the patients were found. The increase in cases continued into July.
Laboratory subtyping can help determine if an increased number of isolates of the same bacterial species results from a common source outbreak. Subtyping methods are based on selected biologic and/or geneticcharacteristics of bacteria that tend to differ between isolates of the same species. In a common source outbreak however isolates typically arise from the same parent organism. These isolates will be similar to each other with respect to these biologic and genetic characteristics and have similar subtyping results.
One subtyping method is DNA fingerprinting by Pulsed Field Gel Electrophoresis (PFGE). In DNA fingerprinting the bacterial DNA is cut into pieces. The pieces are separated by placing them in a jelly-like substance (i.e. the gel) acting as a sieve to which a pulsing electric fieldis applied. The electric field drives the DNA pieces across the gel over a period of hours. The smaller pieces move through the gel more quickly and the larger pieces more slowly resulting in a separation of the DNA into distinct bands. The bands are made to fluoresce and are read under ultraviolet illumination. This DNAfingerprint resembles a bar code. (Figure 1)
Figure 1. Typical DNA banding pattern resulting from PFGE.
Different DNA composition will result in different PFGE banding patterns. Bacteria descended from the same original parent will have virtually identical DNA and their DNA fingerprints will be in distinguishable. Identification of a cluster of isolates with the same PFGE pattern suggests that they arose from the same parent and could be from the same source.
Similar DNA fingerprints alone however are insufficient to establish a linkage between isolates and a common source outbreak. An epidemiologic investigation is necessary to demonstrate that there is a common source and to identify it. To be most useful PFGE subtyping needs to be performed on a routine basis in realtime so that results are available (and reviewed) soon after a case is first detected.
Figure2. PFGE results on E. coli O157:H7 isolates June-July 1997.
Typically a PFGE pattern is defined as having the same banding pattern but including up to one band difference. By this definition isolates #2 3 4 6 and 7 are indistinguishable by these PFGE results. (Isolate #4 differs by one band.)
DNA finger printing performed during the second week of July showed that 17 of the first 19 E. coli O157:H7 isolates from June-July were indistinguishable. They did not match any fingerprints from a convenience sample of isolates frompatients with E. coli O157:H7 infection before May.
Based on the PFGE findings it was suspected the cases of E. coli O157:H7 infection resulted from a common source. On July 15 an investigation was initiated.
Module 1 Natural History of Disease
INTRODUCTION TO EPIDEMIOLOGY: THE EPIDEMIOLOGIC APPROACH
Natural History refers to the course of disease over time unaffected by treatment. Each disease has its own natural history which occurs through a sequence of stages:
Stage of Susceptibility
During this stagethe disease has not developed but the presence of risk factors favor its occurrence. For example high serum cholesterol levels increase the probability of coronary heart disease and would therefore be considered a risk factor.
Stage of Presymptomatic Disease
Duringthis stage the disease process has begun but there are no detectablesymptoms. For example atherosclerosis (hardening of the arteries) occurring before any signs of disease would be considered presymptomatic disease.
Stage of Clinical Disease
Recognizable symptoms occur during this stage of disease. This stage is often subdivided further for better case management and epidemiologic studies.
Stage of Disability
Some diseases resolve completely and do not reach this stage. However there are a number of conditions that leave a person temporarily or permanently disabled. For example stroke can lead to paralysis.
Levels of Prevention
Preventing the natural history of a disease from occurring is an important objective inpublic health. The levels of prevention include:
Primary Prevention
This level of prevention refers to altering susceptibility or reducing exposure tosusceptible individuals (during the stage of susceptibility). Primary prevention includes general health promotion (e.g. good nutrition adequate rest sex education) and specific protective measures (e.g.immunization environmental sanitation).
Secondary Prevention
This level of prevention refers to early detection and treatment of disease (during the pre-symptomatic and clinical stage) . At this prevention level it is sometimes possible to either cure disease or slow its progression prevent complications limit disability and prevent transmission of infectious disease.
Tertiary Prevention
This level of prevention refers to the alleviation of disability resulting from disease and attempts to restore effective functioning (during the disability stage).
Module 1 Mechanisms Of Disease Transmission
INTRODUCTION TO EPIDEMIOLOGY: THE EPIDEMIOLOGIC APPROACH
The method by which an infectious agent escapes a reservoir and enters a host is referred to as mechanism of transmission. There are two main types of transmission: direct transmission and indirect transmission. In direct transmission an infectious agent is immediately transferred from one infected host or reservoir to another. Direct transmission includes not only direct contact such as kissing but also spray by droplets through sneezing and coughing onto the mucous membranes of others. Droplet spread is classified as direct transmission because it occurs over short distancesthe droplets travel a few feet before falling to the ground.
There are three types of indirect transmission: vehicleborne vectorborne and airborne. Vehicleborne transmissionis indirect contact through inanimate objects such as bedding toys surgical instruments and contaminated food. In vectorborne transmissionthe infectious agent is transmitted by an intermediary (usually an insect) to a susceptible host. In airborne transmission two types of particles may be spread through the airdusts and droplet nuclei. Dusts are particles of varying size that result from resuspension of particles that have settled on floors or bedding as well as particles blown by the wind.
Coccidioidomycosis is an example of a disease that is spread by airborne transmission of fungal spores. Droplet nuclei are very tiny particles that may be suspended in the air for long periods of time. They represent the dried residue of droplets from coughing sneezing or the aerosolization of infective materials.
Infectivity
Infectivity is defined as the ability of the agent to invade and multiply (produce infection in a host). An example of a disease with high infectivity would be measles; a disease with low infectivity would be leprosy. Techniques for evaluating infectivity include speed that an agent spreads through a population and proportion of close contacts who become infected.
Immunity
Immunogenicity is defined as the infections ability to produce specific immunity. Immunogenicity can be affected by host factors such as age nutrition dose and virulence of infection.
Herd immunity is defined as the resistance of a group to invasion and spread of an infectious agent based on the immunity of a high proportion of individual members of the group. Herd immunity is believed to be an important factor in the dynamics of propagated epidemics. Factors that are conducive to the development of large-scale person-to-person epidemics include the introduction of an agent to a population that has never been exposed previously and a large number of susceptible individuals with close contact(e.g. prisons convalescent homes).
Incubation Period
The time interval between the exposure of an agent and the onset of illness is referred to as the incubation period. During epidemics of unknown pathogens the incubation period is frequently used to rule out the likely etiologic agent.
Module 1 Reservoirs
INTRODUCTION TO EPIDEMIOLOGY: THE EPIDEMIOLOGIC APPROACH
Reservoirs are defined as the living organisms or inanimate matter (e.g. soil) where an infectious agent lives and multiplies. The concept of the reservoir is important in infectious disease because the reservoir is the component of the cycle where an infectious agent can survive indefinitely. Humans are the main reservoir for most of the viral and bacterial respiratory diseases. Vertebrate animals are reservoirs for diseases such as brucellosis (from cows pigs and goats) anthrax (from sheep) leptospirosis (from rodents) and rabies (from dogs bats and other animals). These diseases that are acquired from animals are known as zoonoses.
Module 1 Variations in Severity
INTRODUCTION TO EPIDEMIOLOGY: THE EPIDEMIOLOGIC APPROACH
An infectious disease may havea wide variety of clinical symptoms ranging from no symptoms to severe clinical illness or death. Diseases such as tuberculosis have a high proportion of asymptomatic individuals (referred to a slow pathogenicity) while diseases such as measles have a high proportion of symptomatic infections and a small percent of severe or fatal illness. Diseases such as the African hemorrhagic fevers caused by Marburg and Ebolavirus are very severe and usually fatal. For diseases with low pathogenicity only a small fraction of cases are often diagnosed and reported.
Module 1 Case
INTRODUCTION TO EPIDEMIOLOGY: THE EPIDEMIOLOGIC APPROACH
Case Assignment
Your task for this case assignment:
Using the materials in the module homepage and in the background section please address the following:
1. Define and describe the field of Epidemiology (1/2 page)
2. Define and explain epidemiologic transition and describe the factors involved in epidemiologic transition (1 page)
3. Say we suspect a relationship between a specific dietary factor and heart disease. Can you think of ways of epidemiologically assessing whether indeed the dietary factor is a determinant of heart disease? (1/2 page)
4. Which types of diseases do you think pose a greater risk for the population of the United States: infectious diseases or chronic diseases. Please explain (1/2-1 page)
Assignment Expectations
Length: Case assignments should be at least 3 pages (750 words) in length.
References: At least two references must be included from academic sources (e.g. peer-reviewed journal articles). Required readings are included. Quoted material should not exceed 10% of the total paper (since the focus of these assignments is critical thinking). Use your own words and build on the ideas of others. When material is copied verbatim from external sources it MUST be enclosed in quotes. The references should be cited within the text and also listed at the end of the assignment in the References section (APA format recommended).
Organization: Subheadings should be used to organize your paper according to question
Format: APA format is recommended for this assignment. See Syllabus page for more information on APA format.
Grammar and Spelling: While no points are deducted assignments are expected to adhere to standards guidelines of grammar spelling punctuation and sentence syntax. Points may be deducted if grammar and spelling impact clarity.
The following items will be assessed in particular:
Achievement of learning objectives for case assignment
Relevance (e.g. all content is connected to the question)
Precision (e.g. specific question is addressed. Statements facts and statistics are specific and accurate).
Depth of discussion (e.g. present and integrate points that lead to deeper issues)
Breadth (e.g. multiple perspectives and references multiple issues/factors considered)
Evidence (e.g. points are well-supported with facts statistics and references)
Logic (e.g. presented discussion makes sense conclusions are logically supported by premises statements or factual information)
Clarity (e.g. writing is concise understandable and contains sufficient detail or examples)
Objectivity (e.g. avoid use of first person and subjective bias)
Module 1 SLP
INTRODUCTION TO EPIDEMIOLOGY: THE EPIDEMIOLOGIC APPROACH
A Multistate Outbreak of E. coli 0157:H7
For your session-long project you will conduct an epidemiologic investigation of an outbreak of E. coli 0157:H7. The grade for the SLP is based on the depth of your work and your ability to analyze the information generate hypotheses about the source of the outbreak and mode of transmission. This means that the student is focusing on those factors of importance to disease transmission control and prevention. A public health perspective will be advanced within the assignment.
Click here to read the background information specific for the module 1 SLP THE MODULE 1 OUTBREAK DETECTION (This is included above)
Your Task for this modular component
Please answer these questions
1. What could account for the increase in cases?
2. Compare the DNA fingerprints in Figure 2 from seven of the E. coli O157:H7 cases. Each isolate has its own vertical lane (i.e. column). Controls appear in lanes #1 5 and 10. Which isolates appear similar? In your opinion was DNA typing necessary in this case? Why?
SLP Assignment Expectations
Length: SLP assignments should be at least 2 pages (500 words) in length.
References: At least two references must be included from academic sources (e.g. peer-reviewed journal articles). Required readings are included. Quoted material should not exceed 10% of the total paper (since the focus of these assignments is critical thinking). Use your own words and build on the ideas of others. When material is copied verbatim from external sources it MUST be enclosed in quotes. The references should be cited within the text and also listed at the end of the assignment in the References section (APA format recommended).
Organization: Subheadings should be used to organize your paper according to question
Format: APA format is recommended for this assignment. See Syllabus page for more information on APA format.
Grammar and Spelling: While no points are deducted assignments are expected to adhere to standards guidelines of grammar spelling punctuation and sentence syntax. Points may be deducted if grammar and spelling impact clarity.
The following items will be assessed in particular:
Achievement of learning objectives for SLP assignment
Relevance (e.g. all content is connected to the question)
Precision (e.g. specific question is addressed. Statements facts and statistics are specific and accurate).
Depth of discussion (e.g. present and integrate points that lead to deeper issues)
Breadth (e.g. multiple perspectives and references multiple issues/factors considered)
Evidence (e.g. points are well-supported with facts statistics and references)
Logic (e.g. presented discussion makes sense conclusions are logically supported by premises statements or factual information)
Clarity (e.g. writing is concise understandable and contains sufficient detail or examples)
Objectivity (e.g. avoid use of first person and subjective bias)
Module 2 Background
MEASURING HEALTH AND DISEASE
Required Readings
Coggon D. Rose G. & Barker D.J.P. (2007) . Quantifying Disease in Populations in Epidemiology for the Uninitiated (4th edition). British Medical Journal. Retrieved on May 22 2012 from: http://www.bmj.com/about-bmj/resources-readers/publications/epidemiology-uninitiated
Supercourse: Rates Ratios and Proportions. (n.d.). Retrieved on May 22 2012 from: University of Pittsburgh Web site: http://www.pitt.edu/