Today is our topic of discussion Definitions in Epidemiology
Definitions in Epidemiology
Susceptibility:
It is the state of being susceptible or become easily affected.
Susceptible host:
A susceptible host (also called a ‘susceptible’) is a member of the population who is at risk of becoming infected by a disease, if he or she is exposed to the infectious agent.
An infectious agent seeks a susceptible host aiming ‘successful parasitism’. Four stages are required for successful parasitism: 1. Portal of entry, 2. Site of election inside the body, 3. Portal of exit and 4. Survival in external environment.
Resistant immunity:
The sum total of body mechanisms that interpose barriers to the invasion or multiplication of infectious agents, or to damage by their toxic products.
Inherent resistance:
An ability to resist disease independent of immunity or of specifically developed tissue responses; it commonly resides in anatomic or physiologic characteristics of the host and may be genetic or acquired, permanen’ or temporary.
Herd immunity:
The chain of infection may be interrupted when a disease agent does not find a susceptible host, which may occur if a high proportion of individuals in a population are resistant or immunized to a disease agent. The immunized persons limit spread to the relatively few unimmunized, who are susceptibles.
This state is achieved through reducing the probability of contact between infected and susceptible persons. This concept is called herd immunity. Practical example of ‘herd immunity’ in our Bangladesh is the OPV. Due to poor sanitary system and socio-cultural status of our country there is chance of immunization of unimmunized childrens.
Portal of entry:
It is the process by which an agent enters a host. Example: Respiratory system, mouth and digestive system, mucous membranes or wounds in the skin.
Portal of exit:
It is the path through which an agent leaves the reservoir. It depends on the site of
growth of the organism. These are –
– Urogenital tract
– Respiratory tract
– Intestinal tract
– Open lesion, skin eruption, blood
– Placenta
Infectious disease:
A clinically manifest disease of man or animals resulting from an infection which can be transmitted to other person.
Emerging infectious disease:
An infectious disease that is newly recognized in a population or has been known for some time but is rapidly increasing in incidence or geographic range.
Re-emerging infectious disease:
A disease rapidly increasing in incidence or geographic range which had previously been present and was eradicated or controlled.
Diseases considered to be re-emerging include avian influenza, West Nile virus, bovine tuberculosis in wildlife, and Lyme disease.
Contact:
A person or animal that has been in such association with an infected person or animal or a contaminated environment as to have had an opportunity to acquire the infection.
Isolation:
As applied to patients, isolation represents separation, for the period of communicability, of infected persons or animals from others in such places and conditions as to prevent or limit the transmission of the infectious agent from those infected to those who are susceptible to infection or may spread the agent to others. In contrast, quarantine applies to restrictions on the healthy contacts of an infectious case
Fomites:
Any inanimate object (as a towel or money or clothing or dishes or books or toys etc.) that can transmit infectious agents from one person to another.
Contamination:
The presence of an infectious agent on the body surface or in clothes, beddings, toys, surgical instruments or dressings, or other inanimate articles or substances including water, milk and food.
Droplets:
A small drop, such as a particle of moisture discharged from the mouth during coughing, sneezing, speaking or singing; these may transmit infections to others by airborne passage.
Dust:
Small infectious particles of widely varying size that may arise from soil, clothes, bedding or contaminated floors and be resuspended by air currents.
Droplet nuclei:
Small residues resulting from evaporation of fluid (droplets emitted by an infected host). They usually remain suspended in the air for long periods of time.
Droplet infection:
An infection acquired by the inhalation of pathogenic microorganisms suspended in particles of liquid exhaled, sneezed, or coughed by another infected person or animal. Example – Chickenpox, common cold, influenza, measles, mumps and tuberculosis (active pulmonary).
Fecal-Oral transmission:
Direct contact is rare in this route, for humans at least. More common are the indirect routes; foodstuffs or water become contaminated (by people not washing their hands before preparing food, or untreated sewage being released into a drinking water supply) and the people who eat and drink them.
Examples – Cholera, Hepatitis A, Polio, Rotavirus, Salmonella etc
Sexual transmission:
This refers to any disease that caught during sexual activity with an infected person. It includes vaginal, anal and oral sex.
Transmission is either directly between genital surfaces or from secretions (semen or the vaginal fluid) which carry infectious agents that get into the partner’s blood stream through tiny tears in the penis, vagina or rectum. Anal sex is more hazardous because penis opens more tears in the rectum than the vagina. Examples are HIV/AIDS, Chlamydia, Genital warts, Gonorrhea, Hepatitis B, Syphilis, Herpes etc.
Vertical transmission:
This is from mother to child, often in utero, during childbirth or rarely via breast milk (also referred to as perinatal infection). Example: HIV, Hepatitis B and Syphilis.
Iatrogenic transmission:
Transmission due to medical procedures, such as injection or transplantation of an infected material.
Contact/Contagious disease:
The disease that is transmitted by direct contact is called contagious. Although all contagious diseases are infectious, not all infectious diseases are contagious. These diseases can also be transmitted by sharing utensils. Example: Impetigo, Scabies, Syphilis (if an uninfected person touches a chancre), Warts, Leprosy etc.
Nosocomial infection:
Nosocomial (hospital acquired) infection is an infection originating in a patient while in a hospital or another health care facility. It has to be a new disorder unrelated to the patient’s primary condition. Examples include infection of surgical wounds, hepatitis B and urinary tract infections.
Opportunistic infection:
This is infection by organisms that take the opportunity provided by a defect in host defense (e.g. immunity) to infect the host and thus cause disease.
Example – Opportunistic infections are common in AIDS and the organisms include herpes simplex, cytomegalovirus and mycobacterium tuberculosis.
Exotic disease:
Exotic diseases are those which are imported into a country in which they do not otherwise occur, as for example, rabies in the UK.
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