Incidence
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CDC epidemiology incidence definition new cases population time
Incidence is the number of new cases of a disease or condition occurring in a specified population during a specified time period.
[
\text{Incidence} = \frac{\text{New cases during a period}}{\text{Population at risk during that period}}
]
Example: If 50 new cases of dengue occur in a population of 10,000 over one year:
[
\text{Incidence} = \frac{50}{10{,}000} = 0.005
]
= 5 per 1,000 population per year.
It measures the risk of developing a disease. In contrast, prevalence includes both old and new cases. Park's Textbook of Preventive and Social Medicine explains that prevalence is influenced by both incidence and duration of illness.
Prevalence
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prevalence epidemiology
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CDC prevalence definition existing cases population
Prevalence is the proportion of a population that has a disease or condition at a specified time or during a specified period. It includes both new and existing cases.
[
\text{Prevalence} = \frac{\text{All existing cases (new + old)}}{\text{Total population}}
]
Example: If 200 people in a town of 10,000 have diabetes today:
[
\text{Point prevalence} = \frac{200}{10{,}000} = 0.02 = 2%
]
Types
- Point prevalence: cases present at one particular point in time.
- Period prevalence: cases present at any time during a stated interval.
Difference from incidence
- Incidence: new cases occurring over time.
- Prevalence: all people currently affected, whether their illness is new or long-standing.
Prevalence generally rises when incidence increases or disease duration becomes longer. The CDC definition of prevalence distinguishes it from incidence on this basis.
Epidemiology
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CDC Principles of Epidemiology definition distribution determinants health related states events
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Epidemiology is the study of the occurrence, distribution, and determinants of health-related events or diseases in specified populations, and the application of this knowledge to prevent and control health problems.
Main components
- Distribution: Who is affected, where, and when
- Person, place, and time
- Determinants: Factors that influence disease occurrence
- Causes, risk factors, exposures, and protective factors
- Application: Using findings to prevent disease and improve population health
Example
If dengue cases rise in one locality during the monsoon, epidemiology examines:
- Who is affected: age, sex, occupation
- Where cases occur: locality or neighborhood
- When cases increase: seasonal pattern
- Why they occur: mosquito breeding sites, water storage, poor vector control
It uses measures such as incidence, prevalence, mortality, and risk to describe disease patterns. Park's Textbook of Preventive and Social Medicine defines epidemiology in these terms.
Etiology
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etiology disease causation
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CDC etiology definition cause of disease
Etiology means the cause or origin of a disease.
It may refer to:
- A single cause, such as Mycobacterium tuberculosis causing tuberculosis
- Multiple contributing causes, such as genetic predisposition, diet, inactivity, and obesity contributing to type 2 diabetes
- An unknown cause, described as idiopathic
Etiology answers: “Why did this disease occur?”
Pathogenesis answers: “By what mechanism does the disease develop?”
Pathogenesis answers: “By what mechanism does the disease develop?”
Risk factor ,pathology, pathogenesis, clinical features,signs,symptoms, investigation, diagnosis, disorder, prognosis, indication, contraindications, treatment, management, complications, precautions give thd definition for each
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NIH NCI Dictionary risk factor pathology pathogenesis prognosis diagnosis contraindication definitions
| Term | Definition |
|---|---|
| Risk factor | A characteristic, behavior, exposure, or condition that increases the likelihood of developing a disease, but does not necessarily cause it. |
| Pathology | The study of disease, including its causes, structural changes in tissues or organs, and effects on body function. It can also refer to the structural changes caused by a disease. |
| Pathogenesis | The mechanism and sequence of events by which a disease develops, from the initial cause to its clinical effects. |
| Clinical features | The findings associated with a disease, including symptoms, signs, and sometimes relevant laboratory or imaging findings. |
| Signs | Objective findings that can be observed or measured by a healthcare professional, such as fever, rash, high blood pressure, or jaundice. |
| Symptoms | Subjective experiences reported by the patient, such as pain, nausea, fatigue, or dizziness. |
| Investigation | Any test or procedure used to evaluate a health problem, such as blood tests, urine tests, imaging, biopsy, or ECG. |
| Diagnosis | Identification of a disease or condition by interpreting the history, examination findings, and investigations. |
| Disorder | A disturbance of normal physical or mental structure or function. It may be acute or chronic and may have a known or unknown cause. |
| Prognosis | The expected course and outcome of a disease, including chances of recovery, recurrence, complications, disability, or survival. |
| Indication | A valid clinical reason for using a particular drug, test, procedure, or treatment. |
| Contraindication | A condition or situation in which a drug, procedure, or treatment should not be used because it may cause harm. It may be absolute or relative. |
| Treatment | Specific measures used to cure, control, reduce, or relieve a disease and its symptoms. Examples include medicines, surgery, physiotherapy, and counseling. |
| Management | The overall plan of care for a patient. It includes treatment plus monitoring, follow-up, prevention, lifestyle advice, rehabilitation, and management of complications. |
| Complications | Additional medical problems or harmful outcomes that arise during or as a result of a disease, treatment, or procedure. |
| Precautions | Actions taken to reduce risk or prevent harm when giving treatment, performing a procedure, or caring for a patient. Examples include dose adjustment, infection-control measures, and monitoring for adverse effects. |
Quick distinctions
- Etiology: why a disease occurs
- Pathogenesis: how it develops
- Pathology: what changes it produces in tissues/organs
- Signs: clinician observes
- Symptoms: patient feels/reports
- Treatment: specific therapy
- Management: complete care plan
A risk factor is something that increases the chance of disease, and prognosis refers to the likely outcome or chance of recovery, consistent with NIH medical terminology.
Incidence, prevalence, epidemiology, etiology definition for each
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CDC epidemiology incidence prevalence definitions
| Term | Definition |
|---|---|
| Incidence | The number of new cases of a disease or health condition that occur in a population during a specified time period. It indicates the risk of developing the condition. |
| Prevalence | The total number or proportion of all existing cases of a disease in a population at a particular time or over a stated period. It includes both new and old cases. |
| Epidemiology | The study of the distribution of health-related events in populations, their determinants or causes, and the use of this knowledge to prevent and control health problems. |
| Etiology | The cause or origin of a disease. A disease may have one cause or multiple contributing causes. |
Simple memory aid:
- Incidence = new cases
- Prevalence = all cases present
- Epidemiology = study of disease patterns in populations
- Etiology = cause of disease
The CDC epidemiology glossary defines incidence as new cases over a specified period and prevalence as cases present in a population.
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