In probability and statistics, a distribution is a function that describes the likelihood of different outcomes in a random event. Simply, it is a frequency plotted as a graph or shown as a table.
How do policymakers decide on whether helmets are compulsory or not while driving two-wheelers or not allowed to smoke in public? And how does WHO decide what healthy eating recommendations to make like salt intake of less than 5 gms per person per day? These are examples of public health decisions made using epidemiology.
Table of Contents
- Epidemiology Definition
- Study in Epidemiology Definition
- What do you mean by the Study of distribution and determinants?
- What are health-related states and events? in Epidemiology Definition?
- Role of Epidemiology & Epidemiologist in Public health
Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations and the application of this knowledge in the control of the disease.
Study in Epidemiology Definition
Now let us understand each word in this definition. Study means gathering evidence. Either by a study on animals in an In-vivo study or in a test tube known as an in-vitro study. But lab studies and studies on animals cannot tell us everything about humans. And we should go for more studies involving real people. But studies on real people are unethical except few conditions. You can’t expose people to potentially dangerous interventions just to see what is happening! This leaves us a choice of observing people in real-world to figure out exposure and its health effects.
What do you mean by the Study of distribution and determinants?
We further explore time place and person distribution. At what time most of the people are affected, are they living close to the exposure in question? What is the age group? Whether men are affected more than women? Exposure doesn’t always mean the occurrence of disease. Availability and accessibility to health services, nutrition, lifestyle, genes, the environment in which we live, and economic stability determine the occurrence of the disease, hence known as determinants of disease.
What are health-related states and events? in Epidemiology Definition?
Indeed, the term health-related states or events may be seen as anything that affects the well-being of the population. Obesity, overweight is a state, so as underweight. many epidemiologists use the term ” disease” for a wide range of health-related states and events. Birth, deaths, and marriage are a few examples of health-related events.
Role of Epidemiology & Epidemiologist in Public health
Policymakers use this information to formulate rules, regulations, and guidelines for the prevention and control of the disease. The role of an epidemiologist is like a detective who tries to solve the puzzle of cause and effect. Which ultimately helps in restoring public health.
Epidemiology is the branch of medicine that deals with the study of the distribution and determinants of health-related states or events (including disease), and the application of this study to the control of diseases and other health problems.
There are several main areas of study in epidemiology, including the study of the distribution and determinants of disease in populations, the design and conduct of epidemiological studies, the analysis and interpretation of data, and the application of epidemiological findings to the control of diseases and other health problems.
Epidemiology is used to study disease by identifying patterns of illness in populations, investigating the causes of disease, and evaluating interventions to prevent or control the spread of disease. Epidemiological methods include observational studies, such as case-control studies and cohort studies, as well as experimental studies, such as randomized controlled trials.
An outbreak is an increase in the number of cases of a disease above what is normally expected in a specific area or among a specific group of people over a particular period of time.
Epidemiology plays a crucial role in controlling disease outbreaks by quickly identifying the cause of the outbreak, determining how the disease is being spread, and implementing control measures to stop the spread of the disease. Epidemiologists also work with public health officials to develop and implement plans to prevent future outbreaks.
Outbreak investigation typically begins with the identification of a cluster or increase in cases of a specific disease or condition. Epidemiologists then collect and analyze data on the cases, including information on symptoms, risk factors, and potential sources of exposure. They use this information to develop hypotheses about the cause of the outbreak and test these hypotheses through further investigation. The ultimate goal of an outbreak investigation is to identify the source of the outbreak and implement control measures to stop its spread.
Epidemiology is used to track the spread of diseases by studying patterns of illness in a population. This can include identifying risk factors for disease, determining how a disease is transmitted, and monitoring the spread of an outbreak. Epidemiology can also be used to evaluate the effectiveness of interventions and public health policies.
Some common epidemiological study designs include case-control studies, cohort studies, and randomized controlled trials. Case-control studies compare individuals with a disease to those without it to identify risk factors. Cohort studies follow a group of individuals over time to see who develops a disease. Randomized controlled trials randomly assign individuals to different groups to test the effectiveness of a treatment or intervention.
Prevalence is the proportion of a population that has a disease at a given point in time. Incidence is the number of new cases of a disease in a population over a given period of time. Prevalence reflects both the number of new and existing cases of a disease, while incidence only reflects new cases.
Epidemiology is a key tool for informing public health policy by providing insight into the spread and impact of diseases on populations. This information can be used to develop and implement effective interventions, such as vaccination programs and public health campaigns, to prevent and control the spread of diseases. Epidemiology can also be used to evaluate the effectiveness of public health policies and interventions over time.
Epidemiological methods include observational studies (such as case-control and cohort studies), experimental studies (such as randomized controlled trials), and surveillance.
A risk factor is a characteristic or exposure that is associated with an increased likelihood of developing a disease or condition.
A confounding variable is a variable that is associated with both the exposure and the outcome, and that may therefore distort the estimate of the association between the exposure and the outcome.
Bias refers to any systematic error in the design, conduct, or analysis of a study that leads to incorrect estimates of the true association between an exposure and an outcome.
A causal relationship is a relationship between an exposure and an outcome in which the exposure is a necessary and sufficient cause of the outcome.
Herd immunity is the resistance to the spread of a contagious disease within a population that results from a high proportion of individuals being immune to the disease, either through vaccination or previous infection.
Bias can be minimized in epidemiological studies by using appropriate study design, careful selection of study participants, careful measurement of exposures and outcomes, and appropriate statistical analysis.
Incidence and Prevalence are two important parameters of epidemiology, which not only help us to measure the burden of the diseases but also help us to understand the disease behavior which intern helps us control the diseases.
Table of Contents
- Is it possible to have a disease where the incidence rate is going down but the prevalence rate is going up?
- Incidence and prevalence both are measures of morbidity.
- Point prevalence
- Period prevalence
- Numerator and denominator in Incidence and prevalence
- How to Calculate Incidence
- Look carefully at your Denominator! In Incidence and Prevalence Calculation
- How to calculate Prevalence in epidemiology?
- Remember incidence is a measure of risk while prevalence is the measure of the disease burden!
Is it possible to have a disease where the incidence rate is going down but the prevalence rate is going up?
Incidence and prevalence both are measures of morbidity.
Incidence and prevalence both are important measures in epidemiology.
Incidence refers to the occurrence of new cases of disease or injury in a population over a specified period of time. Although some epidemiologists use incidence to mean the number of new cases in a community, others use incidence to mean the number of new cases per unit of the population.
Two types of incidence are commonly used — incidence proportion and incidence rate.
Prevalence, sometimes referred to as prevalence rate, is the proportion of persons in a population who have a particular disease or attribute at a specified point in time or over a specified period of time. Prevalence differs from incidence in that prevalence includes all new and pre-existing cases in the population at the specified time, whereas incidence is limited to new cases only.
Point prevalence refers to the prevalence measured at a particular point in time. It is the proportion of persons with a particular disease or attribute on a particular date.
Period prevalence refers to prevalence measured over an interval of time. It is the proportion of persons with a particular disease or attributes at any time during the interval.
Numerator and denominator in Incidence and prevalence
The numbers above the line are known as the numerator and the ones below the line are known as the denominator.
It’s up to you if you want to calculate the rate per thousand then multiply by 1000, or 100 if you want it in percentage!
How to Calculate Incidence
for example in a group of 10 women who were free of disease, 3 develop uterine cancer in a year, so there will be a 3 divided by 10 multiplied by 1000, giving an incidence rate of 300 cases per 1000 population per year.
It is important to note that every person in the denominator must have the potential to be a part of the numerator. In our example these three women have transitioned from a healthy to a diseased state, Incidence is a measure of events, and therefore a measure of risk. So we said that everyone in the denominator must have the potential to become a member of the disease group.
Look carefully at your Denominator! In Incidence and Prevalence Calculation
Let us come back to our example of uterine cancer, suppose the two women have a history of hysterectomy, then they will no longer have the risk of developing uterine cancer and so they have to be removed from the denominator. Recalculating incidence, now instead of 3/10, it would be 3/8 multiplied by 1000 equals the new incidence rate of 375 per 1000 population.
How to calculate Prevalence in epidemiology?
As prevalence is defined as all new plus old cases in the total population at a given point in time. In our previous example if one was the old case then the prevalence would be 4 divided by 10, times 1000, giving a prevalence of 400 cases per 1000 population.
Remember incidence is a measure of risk while prevalence is the measure of the disease burden!
Let’s understand this with an example.
Coronary heart disease prevalence in two cities compared, one is Mumbai and the other is Indore.
In this hypothetical example, Mumbai has a prevalence of 60 cases per 1000 population and Indore has a prevalence of 10 cases per 1000 population.
It looks like the risk of disease is higher in Mumbai!
Well! It’s not. Because prevalence is not a measure of risk but it shows the disease burden in the community.
Let’s look at the incidence rate and duration of disease in both locations.
The incidence rate is five per 1000 per year in both places, but the duration of the disease is 12 Years in Mumbai due to better care, whereas in Indore people die within two years of CHD.
So higher prevalence in Mumbai is just because of the better care prolonging life.
Also, remember Prevalence = Incidence X Duration.
Incidence refers to the number of new cases of a disease or condition that occur in a specific population over a certain period of time. Prevalence, on the other hand, refers to the total number of cases of a disease or condition in a specific population at a given point in time.
The incidence rate is calculated by taking the number of new cases of a disease or condition that occur in a specific population over a certain period of time and dividing it by the total number of individuals in the population at risk during that same period of time.
Prevalence is calculated by taking the total number of cases of a disease or condition in a specific population at a given point in time and dividing it by the total number of individuals in the population at that same point in time.
Factors that can affect incidence and prevalence rates include changes in population size, demographic factors (such as age and gender), lifestyle factors (such as smoking and diet), and access to healthcare.
Incidence and prevalence rates can be used in public health to determine the burden of a disease or condition on a population, to identify high-risk groups, and to evaluate the effectiveness of interventions or treatments.
No, incidence and prevalence rates can vary depending on the population being studied. Factors such as age, gender, lifestyle, and access to healthcare can all affect incidence and prevalence rates.
Prevalence is related to the incidence and duration of a disease or condition. A mathematical relationship that is often used to estimate prevalence from incidence is:
Prevalence = Incidence x Duration
Incidence is the number of new cases of a disease or condition that occur in a specific population over a certain period of time.
Duration is the average length of time that an individual remains affected by the disease or condition.
This relationship is based on the assumption that the duration of the disease or condition is constant for all individuals and that there is no recovery or mortality. In reality, the duration of the disease or condition can vary from person to person, and recovery or death can occur.
It’s important to note that this equation is an approximation and that prevalence can be affected by other factors such as the duration of the disease, the recovery rate, and the mortality rate. In general, a high incidence rate over a short period of time will result in a high prevalence, and conversely, a low incidence rate over a longer period of time will result in a low prevalence.
#epidemiology #psmslectures #risk
The p-value is not enough!- in Epidemiology
In my previous post, we looked at the overview of study designs, which try to establish the relation between exposure and outcome, in other words, whether an association exists or not!
Does exposure always mean the outcome?
Sometimes there may be spurious association because the exposure and outcome is not measured using robust study designs like RCT. For example, there is the high rates of sunburns and also high rates of ice cream consumption during hot seasons. But eating ice cream does not lead to sunburn but this third-factor heat is responsible for both high ice-cream eating and sunburns.
Third factor: Tertium quid – Epidemiology
The error in establishing an association may be due to pure chance, bias, or confounders.
Bias is the systematic deviation from the truth due to faulty study design while confounders confuse us by intermingling with the actual cause, check the video below to understand it better.
Statistics and Effect Size in Epidemiology: Must-have tools!
Amidst the confusion created by confounders and other factors not obviously causing the disease, epidemiologist use statistics and derive conclusions using p-value or probability which measure chance! One step ahead of the p-value is measuring the effect size, how big or large the difference between different exposure and the outcome. For example smoking case cancer 20 times more than red meat (only 0.2 times). Hence, the p-value is not enough!
#confoundingfactors #epidemiology #researchmethods
Definition of Epidemiology
Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations, and the application of the knowledge acquired to control disease in that population or geographical area.
Epidemiology definition is not just a definition but a philosophy
If suppose car seller uses this philosophy, he will look for the distribution and determinants, which increase the sales of car units, this is exactly what business analytics try to do to get more leads and increased sales of their products or services.
What do you mean by study in epidemiological study design?
In simple words, it is a scientific procedure involving answering questions using population data.
Now the way you collect data to increase or decrease the credibility of your answers. Now the way we collect data or information is termed as STUDY DESIGN more appropriately.
Ecological study and case-series
An ecological study is done on groups of people but lacks a comparison, so the latter in which specific people with the same exposure or disease are studied to describe something unusual.
as the human mind understands better when comparison or context has been put, so evolved the comparison studies.
Case-control and Cohort study
As we move from simple observations to comparative or analytic study, collected data becomes more valuable as in a case-control study we can calculate the odds ratio and tell the risk involved with the exposure in question. The same is true for cohort studies where we calculate the Risk ratio. A cohort study overcomes the limitation of a case-control study which is temporal association. (Whether the chicken first or egg!)
Randomised Control Trial (RCT): An interventional Epidemiological study
As analytical studies like cohort and case control are not free of bias and error people have found a way to balance it in both the group by randomized control trial (RCT) where study participants are randomly allocated to each group, and neither participants nor investigators know what intervention they are receiving known as double blinding.
Randomization is the heart of RCT, but we can only randomize people for intervention which is having benefits reported from initial observations, and never something potentially harmful to them.
Systematic review and Metanalysis: Summarize all the relevant studies done using RCT
Where systematic review synthesizes, analyzes, interprets, and summarises the findings, meta-analysis tries to combine all the statistical analysis done on similar studies.
Hierarchy of Epidemiological Studies
The hierarchy of study design exists because of our quest to find the most robust evidence which improves the quality of human life by reducing disease-related morbidity and mortality.
#epidemiology #studydesign #psmlectures
#vectors By Dr Khushboo Hadiya PSM
Vector-borne diseases are a major public health concern, affecting around half of the world’s population. Vectors are living organisms that can transmit infectious diseases between humans or from animals to humans.
Many of these vectors are bloodsucking insects, which ingest disease-producing microorganisms during a blood meal from an infected host (human or animal) and later inject it into a new host during their subsequent blood meal.
Mosquitoes are the best-known disease vector. Others include ticks, flies, sandflies, fleas, triatomine bugs, and some freshwater aquatic snails.
By Dr Khushboo Hadiya PSM
Bayes’ theorem is a fundamental concept in probability theory that describes the relationship between the probability of an event occurring (the prior probability) and the probability of that event occurring given certain evidence (the posterior probability). The theorem is named after Thomas Bayes, an 18th-century statistician and theologian who first published the theorem in his 1763 essay “An Essay towards solving a Problem in the Doctrine of Chances.”
The theorem is expressed mathematically as:
P(A|B) = P(B|A) * P(A) / P(B)
- P(A|B) is the probability of event A occurring given that event B has occurred (the posterior probability)
- P(B|A) is the probability of event B occurring given that event A has occurred (the likelihood)
- P(A) is the probability of event A occurring (the prior probability)
- P(B) is the probability of event B occurring (the marginal likelihood or the normalizing constant)
The theorem is used to update the probability of an event occurring based on new information or evidence. It can be used in a wide range of applications, including decision-making, machine learning, natural language processing, and medical diagnosis.
It is important to note that Bayes’ theorem is based on the assumption of conditional independence, which means that the probability of an event occurring is not affected by the occurrence of other events.
A vector-borne disease is a type of illness that is transmitted to humans (or other animals) by an intermediate host, known as a vector. Vectors are organisms that carry pathogens (disease-causing agents) and transmit them to other living creatures.
Table of Contents
- Mosquito-Borne diseases (Mosquito-Transmitted Diseases)
- Vector Born Diseases
- Control of Mosquitos Using Insecticides
- What Is Integrated Vector Control Measure?
- Different Types of Mosquitoes And Diseases They Spread
- 20 most important things about mosquito-born diseases
Mosquito-Borne diseases (Mosquito-Transmitted Diseases)
Mosquitoes are vectors (organisms that transmit diseases) for a number of diseases. Some of the most common mosquito-borne diseases include:
- Malaria: Malaria is a tropical disease caused by parasites that are transmitted to humans through the bites of infected mosquitoes. It can cause fever, chills, and flu-like symptoms, and can be severe or even fatal if left untreated.
- West Nile virus: West Nile virus is a viral illness that is transmitted to humans through the bites of infected mosquitoes. It can cause fever, headache, muscle weakness, and sometimes a rash or swollen lymph nodes. In rare cases, it can lead to severe neurological symptoms such as encephalitis or meningitis.
- Zika virus: Zika virus is a viral illness that is transmitted to humans through the bites of infected mosquitoes. It can cause fever, rash, joint pain, and conjunctivitis (red eyes). Zika virus infection during pregnancy can cause severe birth defects in infants, including microcephaly (a small head and brain).
- Chikungunya virus: Chikungunya virus is a viral illness that is transmitted to humans through the bites of infected mosquitoes. It can cause fever, joint pain, and rash.
- Dengue fever: Dengue fever is a viral illness that is transmitted to humans through the bites of infected mosquitoes. It can cause fever, headache, muscle and joint pain, and a rash. In severe cases, it can lead to dengue hemorrhagic fever, which can be fatal.
To prevent mosquito-borne diseases, it is important to take precautions to avoid mosquito bites, such as using insect repellent, wearing long sleeves and pants, and using mosquito netting. In some areas, insecticides may be used to control the mosquito population. Vaccines are also available for some mosquito-borne diseases, such as yellow fever and Japanese encephalitis.
Vector Born Diseases
A vector-borne disease is a type of illness that is transmitted to humans (or other animals) by an intermediate host, known as a vector. Vectors are organisms that carry pathogens (disease-causing agents) and transmit them to other living creatures.
- Mosquitoes: Mosquitoes are the most common vectors of diseases. They transmit diseases such as malaria, West Nile virus, Zika virus, chikungunya virus, and dengue fever.
- Ticks: Ticks are vectors of diseases such as Lyme disease, Rocky Mountain spotted fever, and tularemia.
- Sand flies: Sand flies are vectors of diseases such as leishmaniasis.
- Lice: Lice are vectors of diseases such as epidemic typhus and trench fever.
- Fleas: Fleas are vectors of diseases such as the plague.
Control of Mosquitos Using Insecticides
Insecticides are chemical compounds that are used to kill or control the population of insects. Mosquitoes are a common target of insecticides, as they are vectors (organisms that transmit diseases) for a number of diseases, including malaria, West Nile virus, Zika virus, chikungunya virus, and dengue fever.
There are several different types of insecticides that can be used to control mosquitoes, including:
- Pyrethroids are synthetic chemicals that are similar to naturally occurring compounds called pyrethrins, which are found in certain plants. Pyrethroids are effective against a wide range of insects, including mosquitoes, and are often used in mosquito control.
- Organophosphates: Organophosphates are a type of insecticide that works by disrupting the nervous system of insects. They are effective against a wide range of insects, including mosquitoes, but can also be toxic to humans and other animals if not used properly.
- Carbamates: Carbamates are a type of insecticide that works by inhibiting an enzyme that is necessary for the proper functioning of the nervous system in insects. They are effective against a wide range of insects, including mosquitoes, but can also be toxic to humans and other animals if not used properly.
Insecticides can be applied to surfaces or released into the air to control mosquito populations. They can also be applied to clothing or skin as a personal insect repellent. It is important to use insecticides according to the manufacturer’s instructions and to follow all safety precautions to avoid exposure to toxic chemicals.
What Is Integrated Vector Control Measure?
Integrated vector control is a public health approach that combines a range of strategies to control vector-borne diseases. Vectors are organisms that transmit diseases, such as mosquitoes, ticks, and sandflies. Integrated vector control involves using a combination of approaches to reduce the risk of vector-borne diseases, including:
- Chemical control: This involves the use of insecticides to kill or control vector populations.
- Physical control: This involves the use of physical barriers, such as screens, to prevent vectors from entering homes and other buildings. It also involves eliminating standing water (where mosquitoes lay their eggs) and improving sanitation to reduce the breeding sites of vectors.
- Biological control: This involves the use of natural predators or parasites to reduce vector populations.
- Educational and behavioral interventions: This involves educating the public about how to prevent vector-borne diseases, such as using insect repellent and wearing protective clothing.
- Engineering Measures: Mosquitoes lay their eggs in standing water, so eliminating sources of standing water can help reduce the mosquito population. This can be done by emptying containers that hold water (such as buckets, tires, and bird baths), repairing leaks, and properly maintaining pools and other water sources. Proper Storage and Disposal of Solid waste is also very important.
Integrated vector control is a multifaceted approach that aims to reduce the risk of vector-borne diseases in a sustainable and cost-effective manner. It is important to use an integrated approach, as no single strategy is sufficient on its own to control vector-borne diseases.
Different Types of Mosquitoes And Diseases They Spread
|Vector||Disease caused||Type of pathogen|
Rift Valley fever
West Nile fever
20 most important things about mosquito-born diseases
- Mosquitoes are small insects that can transmit diseases such as malaria, dengue fever, and Zika virus.
- Mosquitoes are most active during dusk and dawn and are attracted to the carbon dioxide, lactic acid, and other chemicals produced by humans and animals.
- Female mosquitoes require blood to produce eggs, and they can transmit diseases during the blood-feeding process.
- Mosquitoes breed in standing water, such as in pools, ponds, and ditches, and can lay hundreds of eggs at a time.
- Malaria is the most well-known disease transmitted by mosquitoes and is caused by the Plasmodium parasite. It can lead to fever, chills, and flu-like symptoms, and can be fatal if left untreated.
- Dengue fever is also transmitted by mosquitoes and is caused by the dengue virus. It can cause severe fever, headache, muscle and joint pain, and a rash.
- Zika virus is transmitted by mosquitoes and can cause fever, rash, joint pain, and conjunctivitis. It is particularly dangerous for pregnant women as it can cause birth defects in the baby.
- Chikungunya is another mosquito-borne disease caused by the chikungunya virus. It can cause fever, joint pain, and rash.
- West Nile virus is transmitted by mosquitoes and can cause fever, headache, and muscle weakness. It can also lead to more severe symptoms such as encephalitis and meningitis.
- Using mosquito repellent, wearing protective clothing, and staying indoors during peak mosquito hours can help prevent mosquito bites.
- Eliminating standing water and using screens on windows and doors can also help reduce the mosquito population.
- Insecticide-treated bed nets and indoor residual sprays can help control mosquitoes and prevent the transmission of disease.
- Some species of mosquitoes are more likely to transmit certain diseases than others. For example, Anopheles mosquitoes are the primary vectors of malaria.
- Climate change can affect the distribution and population of mosquitoes, potentially increasing the spread of disease.
- Mosquitoes have developed resistance to certain insecticides, making it more difficult to control their populations.
- The World Health Organization (WHO) recommends integrated vector management (IVM) as the most effective approach to controlling mosquitoes and preventing the spread of disease.
- IVM involves using a combination of methods such as source reduction, biological control, and use of pesticides.
- Vaccines are available for some mosquito-borne diseases, such as yellow fever, but not for others like Malaria, dengue, zika and chikungunya.
- Mosquito-borne diseases disproportionately affect people living in low-income countries.
- Research and development of new tools and strategies, such as genetically modified mosquitoes and disease-blocking vaccines, is ongoing to help control mosquitoes and prevent the spread of disease.