Epidemiology: Ideas, Models, Definitions, Morbidity Rate

The study of disease distribution in human populations and the variables influencing that distribution is known as epidemiology. It is a subfield of medical research that mostly uses statistics. In contrast to other medical specialties, epidemiology often takes a retrospective, or historical, approach and focuses on populations rather than individual individuals. 

It originated in the 19th century from the hunt for human causes, and one of its key responsibilities is to identify people who are more susceptible to a certain disease so that the reason may be found and preventative measures can be taken.

Also Read: Marfan Syndrome: Causes , Symptoms, Diagnosis, Treatment

In order to get a deeper understanding of the features of disease both within and within populations, epidemiologists employ a range of measures, such as death rates as well as incidence and prevalence rates. Furthermore, epidemiologic studies can be categorized as analytical or descriptive based on whether their goal is to test hypotheses derived from laboratory observations or descriptive surveys or to characterize the illness. 

Epidemiologic study data is often utilized in the planning of new health services and in assessing the general health condition of a certain group. Public health officials routinely compile epidemiologic data on certain diseases and the death rates of their populations in the majority of the world's nations.

Epidemiology's area is quite multidisciplinary. Not only does it have strong connections to statistics, especially biostatistics, but it also heavily draws from the theories, concepts, and knowledge of the behavioral and social sciences (anthropology, psychology, and sociology) as well as the health and biomedical sciences (biology, pathology, and physiology).

Also Read: Asha: Accessibility, Functions, Obligations, Compensation, Benefits And Facilitators of Asha

Essential Ideas And Resources

Two basic presumptions underlie epidemiology. Firstly, the chance of contracting an illness is not random rather, it is influenced by several circumstances. Second, demographic studies make it possible to pinpoint the origins of the disease and its preventative elements. Epidemiologists use a variety of tools, the most fundamental of which are rates, together with models and definitions of illness incidence to study disease in communities.

Also Read: Screening of Disease

Models Of Epidemiology

Models are frequently used by epidemiologists to explain why diseases develop. A popular model explains illness in terms of exposure variables and susceptibility. People need to be exposed to the disease as well as vulnerable to it in order for them to get sick. 

For instance, a person has to be exposed to someone who is shedding the measles virus (an active case) and does not have immunity to the illness in order to contract measles (rubeola), a highly contagious viral disease that was previously widespread in youngsters. One can become immune to measles by receiving a vaccination or by having experienced the illness in the past.

The epidemiologic triad, often known as the epidemiologic triangle, is another widely used paradigm that sees the balance of host, agent, and environmental variables as the cause of illness incidence. The recipient or sufferer of the sickness, whether real or prospective, is known as the host. Hosts possess traits that can make them more vulnerable to illness or shield them from it. 

These traits might be behavioral (like habits, culture, and way of life), social (like attitudes, norms, and values), or biological (like age, sex, and immune level). The thing that causes sickness is called the agent. Agents might be nutritional (like food additives), physical (like ionizing radiation), chemical (like gasses and natural or manmade chemicals), or biological (like germs and fungus). 

Also Read: Classification Of Epidemiological Studies

Everything outside the host and agent that affects health is considered part of the environment. The three types of environments that make up the environment are the physical environment (such as weather patterns), the biological environment (such as plants and animals), and the social environment (such as political, legal, and economic). 

One may use the example of lung cancer to demonstrate the epidemiologic trio. 

The individual with lung cancer is the host. They may have smoked for a long time as a habit. The smoke, tars, and harmful substances found in tobacco are the agents. The setting might have been places where it was legal to smoke at work and places where tobacco items like cigarettes were easily accessible.

Also Read: The Spectrum of Disease and The Iceberg Phenomenon

Definitions Of The Incidence Of Diseases

Epidemiologists categorize a population as either endemic or epidemic based on the kind of illness cases and the frequency of disease incidence. An endemic illness is one that typically affects a community. On the other hand, an epidemic is a marked and abrupt rise in the prevalence of a disease within a community. It can also be the initial instance of a completely novel illness. A pandemic, or quickly spreading outbreak of a disease affecting populations over a large geographic region, might originate from an epidemic. 

Pandemics frequently affect the entire planet. As an example of the three categories, a tiny percentage of people in a major metropolis may have influenza every year; these people would be regarded as endemic instances of the illness. An epidemic is declared when a city has a significant rise in the number of influenza cases during the winter months. 

A new strain of influenza that spreads quickly and affects individuals all over the world is referred to as a pandemic. 

Also Read: Vaccines & Cold Chain

Crude, specific, and adjusted rates

Epidemiological rates can be categorized as adjusted (standardized), particular, or crude. In their computations, crude rates take into account both the total population and the number of illness cases. Cases and populations are distinguished by specific rates according to characteristics such as race, age, sex, or etiology. It is possible to compare populations with various characteristics using adjusted rates.

Rates of mortality and morbidity

A number of epidemiological studies are based on the examination of morbidity and death resulting from acute and chronic illnesses. Whereas mortality is the death brought on by a disease, morbidity is the illness, symptoms, or impairments caused by a disease. Acute illnesses occur suddenly and go away in a month or less (chickenpox, influenza, etc.). 

Long-term conditions are known as chronic illnesses, and many of them like diabetes mellitus and many types of cancer are incurable. Researchers can compare illness cases and fatalities to the population unit size by using morbidity and mortality rates. A rate is a unique kind of percentage in which the denominator contains the numerator of the proportion plus a time specification. 

Any handy format, such as per 1,000, per 10,000, or 100,000, can be used to describe rates. For example, infant mortality rates are usually reported as a percentage of live births, whereas cancer rates are reported as a percentage of the population.

Also Read: Clinical Trials: Animal and Human Study

Rates Of Incidence And Prevalence

Incidence and prevalence rates can be used to quantify the frequency of illness. The incidence rate calculates the number of new instances of a disease that occur within a community over time. The incidence rate has implications for upcoming issues in healthcare and is a crucial metric for assessing disease-control initiatives. For instance, determining the incidence rates of HIV/AIDS might provide information about the disease's spread and the effectiveness of HIV preventive initiatives.

The total number of cases of a disease that exist in a community at any one moment or over an extended period of time is measured by the prevalence rate. An effective measure of how much a disease is affecting the social and medical systems in a given area is its prevalence rate. Only chronic disorders that last for months or years can benefit from it. For instance, prevalence rates within nations can be used to estimate the financial, social, and medical costs associated with AIDS.

The frequency and duration of the condition both directly affect prevalence rates. Prevalence will be high in comparison to incidence if a disease has a lengthy duration but a low incidence, as is the case with chronic illnesses. On the other hand, a disease's prevalence will be lower than the incidence if it has a brief duration (caused by recovery, migration, or death).

Sources Of Information About Epidemiology

To determine rates and carry out research, epidemiologists employ primary and secondary data sources. Original information gathered by an investigator for a particular goal is known as primary data. 

For instance, in order to determine which particular items were ingested, an epidemiologist may interview individuals who feel unwell after dining at a restaurant in order to get primary data. Since gathering primary data is costly and time-consuming, it is often reserved for situations in which secondary data is unavailable. Secondary data is information gathered by other people or organizations for a different reason. 

Birth and death certificates, population census records, patient medical records, disease registries, insurance claim forms, billing records, public health department case reports, and surveys of individuals and households are a few examples of secondary data sources that are frequently used in epidemiological studies.

Analytical And Descriptive Epidemiology

The distribution of disease within a community is described using descriptive epidemiology. It explains the features of the illness incidence in terms of person, place, and time. Conversely, analytical epidemiology tests theories to see if there are statistical relationships between putative causes and the prevalence of disease. 

It is also employed in the evaluation of therapeutic and medical therapies' efficacy and safety. Four main research study designs are used to investigate analytic epidemiology: cross-sectional studies, case-control studies, cohort studies, and controlled clinical trials.

Studies that examine the relationships between an illness and relevant factors are called cross-sectional studies. For instance, the amount of radon gas in the houses of lung cancer patients may be examined in a cross-sectional research intended to determine if exposure to the radioactive gas radon at home raises the risk of lung cancer. 

One benefit of cross-sectional studies is that they are easy and inexpensive to perform. The primary drawback of their approach is that it only establishes connections, not causality. In case-control studies, an appropriate control group without the disease and individuals with a specific disease (cases) are compared for their exposure to the factor suspected of causing the disease. 

The best way to determine the source of uncommon occurrences, such as uncommon malignancies, is through case-control research. The advantages of case-control studies are their low cost and speed of execution, as well as their low requirement for the number of cases and controls. Their primary drawback is that they rely on records or recollections, both of which might be biased, to ascertain exposure status.

Cohort studies are observational research projects that track a specific group of people (the cohort) throughout time and compare the results for those who were exposed to a factor at varying degrees and those who were not. Cohorts can be discovered from historical data (a historical cohort study) or formed in the present and tracked into the future (a contemporaneous cohort study). 

Cohort studies provide the primary benefit of determining the direction and timing of occurrences. Their primary drawbacks are the length of follow-up periods and the need for high sample numbers. Furthermore, they are not appropriate for researching uncommon illnesses.

Studies that test medicinal medications or other health or medical interventions to determine their safety and efficacy are known as controlled clinical trials. The results of a novel medication or intervention administered to an experimental group are compared to those of a control group that does not receive the same medication or intervention in a controlled clinical trial. 

Clinical trial participants may be randomized to the experimental and control groups to reduce bias. Before being released to the general public, novel medicinal substances, and medical technologies must pass stringent regulated clinical studies in several nations. Although controlled clinical trials are exceedingly expensive to run, they have the significant benefit of providing impartial data.

Download the PrepLadder app now to access high-yield content with 24-hr Free Trial. Explore premium study resources like Video Lectures, digital notes, QBank, and Mock Tests for a seamless exam preparation. Time to begin NEET PG preparation courses online with PrepLadder.