It is important to note that an endemic disease or cluster can become an epidemic. An example of this would be with malaria; although malaria is endemic to certain regions in South America, Africa, and South Asia, during certain years or times it can become an epidemic with higher number of cases then usual present in the population. In addition, it is also possible for epidemic or outbreak to progress and become a full fledged pandemic.
Rates refers to the number of cases occurring during a specific period of time and depends on the population size at that time. Calculating disease rates helps epidemiologists to compare health issues among different populations. The general calculation for determining disease rate is to divide the number of cases or health condition by the number of population at risk during a specific period of time, and multiplying that by 100. However, disease rates can also be differentiated into two different types: prevalence rate and incidence rate.
Prevalence rate refers to the number of both old and new cases in a population during a specific time period, which is divided by the total number of cases in the population. Prevalence rates are useful when dealing with investigations relating to chronic diseases, which last for more than 3 months. On the other hand, incidence rate refers to the number of new health related conditions or cases which is divided by the population at risk. Incidence rates are important in studies involving acute diseases, where symptoms of a disease peak and subside within days or weeks and generally lasts less than 3 months.
Epidemiological studies makes use of both experimental and observational studies. Experimental studies are ones where the epidemiologist can control and manipulate different variables throughout the experiment, and usually involves a placebo treatment/group. This type of study is used when epidemiologists are trying to determine the cause of a health issue/disease or evaluating the effectiveness of a cure or interventions. Observational studies include descriptive and analytical studies; descriptive studies investigates epidemiological cases with regards to TPP while analytical study investigates hypothesis regarding relationships between health issues and risk factors. While descriptive studies (TPP) answers questions of when, who, and where, analytical studies tries to answer the question of how a population is affected by a disease and why they are affected. Overall, observational studies do not manipulate any variables and often uses comparison groups for analysis; this type of study is often done in an attempt to discover the links between exposure to certain risk factors and health outcomes. Some examples of observational studies include cohort studies, case-control studies, and cross-sectional studies.
Investigating an outbreak is a very involved multi-step process which ranges from first establishing the existence of an outbreak to communicating the findings of the investigation with the scientific community as well as the general population. The following is a rough sequence of the process of these investigations.
Epidemiology is a multidisciplinary subject. Members in this field mostly includes public health care workers and scientists from related fields such as chemists, biologists, geneticists, and anthropologists. People in epidemiology may work in hospital and research settings, as well as for federal organizations such as the Centers for Disease Control and Prevention (CDC). One particular unit that may be of interest for those pursuing epidemiology is with with Epidemic Intelligence Service (EIS), a subgroup within the CDC specializing in epidemiology. Epidemic Intelligence Service officers are field workers who investigate outbreaks in the US and other countries. Their work aids in understanding causes of outbreaks and quickly stopping spread of diseases from one place to another; notably, they have contributed to helping during various pandemics in the past, such as with smallpox, polio, and Ebola.
One particular field that has had an impact in epidemiology is anthropology. In the past, cultural anthropologists have been a very helpful resource in bridging the gap between different countries/cultures and the epidemiological investigators. They have helped and continues to help with the development and implementation of preventative/control measures in countries in a manner that will not conflict with societal beliefs or values, which may get in the way of treatment or stopping the spread of an outbreak.
In recent years however, medical anthropology in particular has taken on a larger role in the field of epidemiology. Medical anthropology looks at biological, social, cultural, and linguistic anthropology to understand how these factors influence health and well-being, experience and distribution of illness, as well as prevention of treatment. As with cultural anthropologists, medical anthropologists have continued to aid in the development of public health policies. In particular, they have been very helpful in providing a unique perspective on public health discourse. For example, they investigate how culture affects research studies, are able to pick up on seemingly "irrelevant" yet important small details that a epidemiologist might miss, and they are able to provide qualitative data whereas epidemiology only focuses on quantitative data. One main thing of importance here is that while epidemiologist has largely ignored cultural factors when looking at the causes of diseases/health conditions, medical anthropology has challenged this notion and contributed to the field by showing how culture and social factors play a big role in people's willingness to follow public health guidelines/interventions or even accept treatment for their illnesses.
Whereas the nature of epidemiological investigations may lead to a reductionist or limited point of view, medical anthropology provides a more holistic view of the problem and examines the issue from different angles to best understand and help the populations in need. Another critical contribution of medical anthropology has been with regard to critical qualitative data. While epidemiology is focused mainly on quantitative data and trends in health of the population, medical anthropology provides rich source of information on understanding the population's subjective experiences and providing qualitative data explaining why a particular intervention or treatment may have failed among a particular population. Their main contributions in recent years have come from modifying and helping develop epidemiological surveys by taking into account word choice and the "social suitability" of questions, so that responses would be more accurate and thereby helping to increase the validity of the questionnaires. It has also been found that medical anthropologists have played a large role in helping locals better understand the objectives of epidemiologists and thereby helped them become more receptive of their investigations. In addition to all these, one of the major contributions of medical anthropology has come from it's ability to help explain health phenomenon and create and test hypothesis relating to such explanations, in a way that epidemiologists have been unable to due to their strict focus on quantitative data. In short, while epidemiology is good at understanding numerical patterns and biological causes for disease/health conditions, it is unable to fully explain all the factors that underlie certain diseases/health conditions, and this is a gap that medical anthropology has been able to pick up on and complement by providing rich qualitative data which looks at health and diseases from a holistic perspective.