Epidemiology is the study of the distribution and frequency of health problems and diseases. It also focuses on their determinants in human populations. The study mainly considers features of a population because, as a methodology, it is suited for such work. It answers four questions about the problem or disease including, what is the problem, frequency, who is infected, where and when does it occur and why does it occur in the given population (“What is Epidemiology LO 1.1.” 16-18).
The types of epidemiology studies differ. There are descriptive, analytical, experimental variations, each with its purpose. Nevertheless, they all fulfill the main purpose, which is to obtain, interpret and use health information appropriately. For example, one question answered is who gets a disease and why. An epidemiologist aims to collect information about the sick and those who are well and then study the differences in the way sickness comes to exist in the given population. While looking at the disease, the focus expands to look also at mortality, hospitalization, disability, quality of life, and health status. The right answer might not pop up directly from a study.
Therefore, epidemiology is about weighing and balancing information about causes and outcomes. It is the use of comparison and contrast. It also uses rates of events per the population at risk. In fact, when simplified, epidemiology shows the number of people who were affected per the total population facing the same risk (“What is Epidemiology LO 1.1.” 16-18).
Epidemiology comes from the word epidemics, which makes it the study of epidemics. These are events where more than the initially estimated numbers of people get the same disease at a given period. When studying diseases, epidemiologists will look at the etiology. This can be for disease or unhealthy conditions. They seek to find the primary agent responsible, the characteristics of the agent or the factors causing the condition, transmission mode, contributing factors, and the geographic patterns of spread. Practitioners can use the information presented by epidemiology to report, describe and determine the natural course of health conditions, plan and develop parts or whole health services and programs, and offer administrative and planning data. In the United States, epidemiology has led to the determination of the leading causes of death, which include heart disease, neoplasm, cerebrovascular disease, and diabetes mellitus. With the information that epidemiology provides, its results fit being used as the basis for developing disease control and creation of prevention measures for the population segments that are at risk.
Based on the intentions of epidemiology, there are two common types of the study, descriptive and analytic. The first type involves an examination of the distribution of disease in a population. It includes observation of the basic features of the disease’s distribution. The second type begins with a hypothesis that tests the cause of a given disease. It studies how exposures relate to the disease. The second type comes after the first given that it needs information on where to look, what to control so that it develops an appropriate hypothesis. In the descriptive study, epidemiologists examine the person, place, and time. The features of the three categories of areas to look at are examined deeper in each case. For example, for the person, the epidemiologist will consider age, ethnicity, gender, concurrent disease, risk-taking behavior, and education or occupation among other things.
The collection of information on surveillance is by surveys, and the target populations for the survey are people related to the victim in different ways such as survivors, next of kin, and neighbors. Questions included in the survey inform the researcher about the person, place and time characteristics of the condition or disease being studied. Once the study moves from descriptive to analytical, the basis of focus also changes from people, place and time to host agent and environment. According to the epidemiologic homeostasis, host, environment and agent relations form a pyramid. For the host, analytics considers personal traits, immunologic factors, behaviors, genetic predisposition as they influence the chance of disease or its severity. For agents, the consideration is on biological, physical and chemical as they facilitate the occurrence of disease. Finally, for the environment, the focus is on external conditions, physical or biological and social factors in the way they contribute to the disease process.
Host, agents, and environmental factors are always in balance, and when they are not, epidemics occur. Imbalance arises due to new agents, changes in existing agents, changes in the number of susceptibles in the population and environmental changes affecting the transmission of the agent or the growth of the agent. Once the demographic distribution, geographic distribution, seasonal patterns and frequency of disease patterns are established, they serve the allocation of resources, planning programs and hypotheses development. When conducting analytical epidemiology, the focus is on the relationship between exposures and effects.
Globally, communicable diseases are the salient cause of morbidity and mortality in emergencies. The main causes of these outcomes are diarrheal diseases, acute respiratory infections, measles and in some cases endemic malaria. In the past, meningococcal disease, tuberculosis, and relapsing fever, as well as typhus, have caused epidemics. Some populations affected by emergencies suffer from malnutrition and trauma, which cause disease and death. In the case of an emergency, shelter, water, sanitation, food and basic health care are needed to protect the health of victims. Humanitarian responses use a systematic approach. The approach presents the fundamental principles of controlling communicable diseases, which are rapid assessment, prevention, surveillance, outbreak control and disease management.
When managing a communicable disease outbreak, the responders prepare, detect, respond and evaluate their involvement. Preparation involves coordination meetings, a strong surveillance system, an outbreak response plan for each disease, and stocks of antibiotics and vaccines and other resources including laboratory support. Detection happens through surveillance systems that have an early warning system for epidemic-prone diseases, contact with the respective ministry of health and the world health organization (WHO), which globally coordinates responses. The appropriate specimens are taken for laboratory confirmation, and a weekly report of the case is presented. The response covers confirmation of the outbreak, activation of the outbreak control team, investigation of the outbreak and control of the outbreak. The evaluation assesses the appropriateness and effectiveness of the containment measures used and the timelines of the outbreak detection and response. It includes changing public health policy if indicated and writing and disseminating outbreak reports.
Some best practices are in use for preventing and control of common communicable diseases. For acute respiratory infections, early recognition and treatment are encouraged. All children with coughs are carefully accessed, and supportive measures are used. Vaccinations against measles, diphtheria and whooping cough help to reduce the impact of the infections. In the case of cholera, prevention and control are by the establishment of treatment centers with barrier nursing, proper disposal of fecal material and vomit and promotion of washing hands with soap and water when handling food. Other diarrheal diseases also require a safe water supply, which is reasonably clean. Conjunctivitis prevention and control measures include disinfection of articles contaminated by nasal and conjunctival discharges. Dengue is another common communicable disease whose epidemics are prevented and controlled by eliminating habitats of Aedes mosquitos, personal protection against mosquito bites and surveys that determine vector density and larval habitats. Larvicide is used when there is an outbreak, and it is applied to all potential habitats. Social mobilization is also done to eliminate breeding sites. Other diseases that have specific prevention and control strategies include relapsing fever, trypanosomiasis, yellow fever, HIV/AIDS and malaria.
Surveillance covers the health care system and the public health authority. It includes the event, the data, information and intervention all related in a cyclic process (“Communicable Disease Surveillance LO2.1.” 11-14). One process is informed by the previous one, and it informs the design and strategy used to the next. Surveillance serves monitoring and controlling needs while research is for contributing to knowledge about a given phenomenon. Surveillance requires understanding the problem and then identifying opportunities for prevention and control. It must pursue specific, measurable, action-oriented, and timed objectives. In surveillance, the data needed would include the number of cases and number of resistant strains on one side as an example. The other side of comparison would include population under surveillance, live births, and bacterial isolates as examples. The issues that will affect the choice and use of a source of data will include costs, data quality, timeliness, commercial sensitivity, comparability, and representativeness. When designing, one has to consider also sampling vs. comprehensive approach, aggregated vs. individual data and active vs. passive approaches. The other issues are confidential vs. anonymous approaches and the security involved. They are similar to research design considerations.
The analysis is often descriptive and can use time series, outbreak detection, molecular epidemiology and geographical information systems (GIS) options. The results are interpreted by system and data characteristics, and changes are observed. The chance, bias, and truth are considered. When setting up the dissemination of information, practitioners will consider the development of outputs in consultation with users. They will look at the appropriate level of detail for action, regular review of usefulness and avoidance of information overload. After evaluating whether the system designed and used served its purpose as expected, the following surveillance challenges can be reported. First, stakeholders must ask whether it was surveillance or it was research, which was needed. Second, they check reliability and sustainability. They also consider new threats and timeliness as well as human rights. Each of these parameters is a challenge. After surveillance, the report can be in the form of periodic reports, newsletters, and annual reports for the ongoing activities. They can be compared to identify trends.
Outbreak investigations consider descriptive parameters or who, what, when, why and how questions. They use person-to-person modes, common source modes, and vector-borne modes. Their design can be descriptive, case-control, or case-case. In investigations, clustering helps to identify and remove or control cases and effects. Clustering can be temporal or spatial. In other cases, surveillance can be enhanced especially when the intention is to guide policymaking. It includes traditional surveillance and other methods such as increased analytic possibilities or standardized data collection. Another surveillance type is sentinel, which does not seek completion and relies on specific sources of information for filling a particular purpose. Once there are positive findings, they will initiate other surveillance. The sentinels are often passive and have flexible, relevant objectives suggested by participants. The link to professional organizations.
Epidemiological research can be lab research, epidemic investigations, or population-based (field) research. It uses primary and secondary data collection methods and covers qualitative or quantitative research design. The quantitative design can be experimental or observational. Observational research design can be a basis, hybrid or incomplete. In qualitative methods, the epidemiologist uses focus groups, interviews, surveys, self-reports, observations and document analysis (“Study Designs in Epidemiology” 6-7). For quality assurance of the same method, the focus is on trustworthiness and authenticity. Meanwhile, for authenticating quantitative designs, the epidemiologists will be concerned with reliability internally and externally and validity regarding construct, content and face.
Analytical epidemiology research covers the questions of why and how while descriptive epidemiology deals with the initial questions of who, what, when and where. An analytical approach will help to identify the cause of the disease. It involves research for testing hypotheses that are created by descriptive epidemiology. It considers the exposure and outcomes of cases. A case is some standard diagnostic criteria that are needed to identify a person as an attribute of a particular disease. With experimentally designed studies, individuals or communities can participate. A common type is the randomized clinical trial. The table below helps to summarize major designs and uses of analytical epidemiology studies.
|Study||Main criteria||Best for||Criticism|
|1||Randomized control trial (RCT)||Assignment of exposure is random. The non-exposed group is untreated or receives standard treatment.||Yielding an estimate of the effect that is unbiased and consistent||Results may not be the generalization to the whole population (Clay 52). |
The research also leaves out critical information needed such as which patients are to benefit from the treatment
|2||Cohort study||Study population grouped by exposure status, groups followed in future to determine the outcome. A retrospective would have past access of the group and review of outcome that has already occurred. |
Uses observational strategies
|Members can easily be identified and accessed, exposure is rare and multiple diseases may be involved||They introduce a risk of bias, is often expensive regarding resources|
|3||Case-control study||Uses observational strategies||Situations where identification of the entire cohort will be too costly or time-consuming and access would face the same challenges Illness is rare.||There are significant differences in quality of information with cases researched thoroughly |
Case and controls may have different recalls of specific exposures and events relevant to the studied disease outcome (Boston University School of Public Health par. 2).
|4||Cross-sectional studies||Determination of exposure and outcome is simultaneous. |
Uses observational strategies
Measurement is taken once
|Good for situations that need simplified reports such as descriptive studies||Have limited function in demonstrating causal inference and cannot test the temporal relationship between disease outcomes and exposure|
|5||Case report||A detailed description of disease occurrence happens |
Only deals with an individual.
Looks for unusual features of the case to suggest a new hypothesis
|Works when a detailed description of a single subject is needed||The design is useful when it is part of other studies and by itself, it yields little generalizable information.|
|6||Ecological study||Uses observational strategies||Useful for comparing the occurrence of disease between groups that have different levels of exposure||It works only at the group level.|
|7||Clinical experimental study||The researcher controls the exposure that individuals get.||Best for situations where patients are available and treatment is being tested||Does not work for group-level exposure, only works for individuals|
Infectious diseases are approached in an epidemiological way with surveillance designs. They include traditional disease notification, outbreak investigation, enhanced surveillance, sentinel surveillance, emerging infectious diseases surveillance using diagnosis or syndromic options, and molecular biology and surveillance. Each design includes systematic collection, consolidation and evaluation of morbidity and mortality reports and additional relevant data. It excludes the actual control activities. It is easy to confuse surveillance and research as they both include the collection of information; however, the following parameters help to explain their major differences (CDC par. 2-10). Surveillance is ongoing and generates hypotheses. It is incomplete data on population and uses simple analysis. It is the rapid dissemination of results, and they do not have to generalize to wider populations. The results trigger an intervention. On the other hand, in research, the process is time-limited; it tests a hypothesis, uses complete data on the sample and relies on complex analysis. It is also slower on the dissemination of results. The research aims to generalize the findings, and this can have a loose link to the actual intervention intended.
“Communicable Disease Surveillance LO2.1.” Lecture Presentation
“Study Designs in Epidemiology.” Lecture Presentation
“What is Epidemiology LO 1.1.” Lecture Presentation.
Boston University School of Public Health. “Advantages and Disadvantages of Case-Control Studies.” School of Public Health, 2015. Web.
CDC. “Lesson 6: Investigating and Outbreak.” Centers for Disease Control and Prevention, 2012. Web.
Clay, Rebecca A. “More Than One Way to Measure.” Monitor on Psychology 2010. Web.