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Medical Dictionary


infection (in-fek′shun)
Invasion of the body with organisms that have the potential to cause disease. agonal i. SYN: terminal i.. airborne i. a mechanism of transmission of an infectious agent by particles, dust, or droplet nuclei suspended in the air. apical i. implantation of microorganisms at the apex of a tooth, usually the result of the migration of microorganisms from the pulp canal through the apical foramen. cross i. i. spread from one source to another, person to person, animal to person, person to animal, animal to animal. cryptogenic i. bacterial, viral, or other i., the source of which is unknown. disseminated gonococcal i. i. from Neisseria gonorrhea which is spread to distant parts of the body beyond the original portal of entry (usually the lower genital tract). Usually manifest by rash and arthritis. droplet i. i. acquired through the inhalation of droplets or aerosols of saliva or sputum containing virus or other microorganisms expelled by another person during sneezing, coughing, laughing, or talking. endogenous i. i. caused by an infectious agent already present in the body, the previous i. having been inapparent. focal i. an old term that distinguishes local infections (focal) from generalized infections (sepsis). inapparent i. presence of i. in a host without the occurrence of recognizable symptoms or signs. latent i. an asymptomatic i. capable of manifesting symptoms under particular circumstances or if activated. mass i. i. resulting from the entrance of a large number of pathogens into the circulation or tissues. mixed i. i. by more than one variety of pathogenic microorganisms. pyogenic i. i. characterized by severe local inflammation, usually with pus formation, generally caused by one of the pyogenic bacteria. Salinem i. SYN: Salinem fever. scalp i. an i. external to the galea; e.g., folliculitis or cellulitis. secondary i. an i., usually septic, occurring in a person or animal already suffering from an i. of another nature. terminal i. an acute i., commonly pneumonic or septic, occurring toward the end of any disease and often the cause of death. SYN: agonal i.. urinary tract i. (UTI) microbial i., usually bacterial, of any part of the urinary tract; can involve the parenchyma of the kidney, the renal pelvis, the ureter, the bladder, the urethra or combinations of these organs; often the entire urinary tract is affected; the most common organism causing such i. is Escherichia coli. vector-borne i. class of infections transmitted by an insect or animal vector. The vector may merely be a passive carrier of the infectious agent, but many kinds of infectious agents undergo a stage in biological development in the vector, i.e., the vector, as well as the human host, is essential to the survival of the infectious agent. Vincent i. SYN: necrotizing ulcerative gingivitis. zoonotic i. an i. shared in nature by humans and other species of animals.

See infection immunity.

infectiosity (in-fek-she-os′i-te)
SYN: infectiousness.

infectious (in-fek′shus)
1. A disease capable of being transmitted from person to person, with or without actual contact. 2. SYN: infective. 3. Denoting a disease due to the action of a microorganism.

infectiousness (in-fek′shus-nes)
The state or quality of being infectious. SYN: infectiosity.

infective (in-fek′tiv)
Capable of transmitting an infection. SYN: infectious (2) .

infectivity (in-fek-tiv′i-te)
1. The characteristic of a disease agent that embodies capability of entering, surviving in, and multiplying and causing disease in a susceptible host. 2. The proportion of exposures in defined circumstances that result in infection.

infecundity (in-fe-kun′di-te)
SYN: female sterility. [L. infecunditas, barrenness]

inference (in′fer-ens)
The logical process of passing from observations and axioms to generalizations; in statistics, the development of generalizations from sample data, usually with calculated degrees of uncertainty.

inferior (in-fe′re-or)
1. Situated below or directed downward. 2. [TA] In human anatomy, situated nearer the soles of the feet in relation to a specific reference point; opposite of superior. 3. Less useful or of poorer quality. SYN: Lower. [L. lower]

inferiority (in-fer-e-or′i-te)
The condition or state of being or feeling inadequate or inferior, especially relative to one's peers or to others similarly situated.

infertility (in-fer-til′i-te)
Diminished or absent ability to produce offspring; in either the male or the female, not as irreversible as sterility. [L. in- neg. + fertilis, fruitful]

infest (in-fest′)
To occupy a site and dwell ectoparasitically on external surface tissue, as opposed to internally (infect). [L. infesto, pp. -atus, to attack]

Development on (rather than in) the body of a pathogenic agent, e.g., body lice. SYN: ectoparasitism.

infibulation (in-fib-oo-la′shun)
Closure of the vaginal vestibule by creating a fusion of the labia majora; typically done after excision of the labia minora and clitoris and incision of the labia majora to create raw surfaces that can be surgically joined by pinning so that they will eventually grow together; done for cultural, not medical, reasons. SEE ALSO: female circumcision. [L. infibulo, to pin or clasp together, to join surgically (Celsus), fr. in- + fibula, pin, clasp]

infiltrate (in′-fil-trat, in-fil′trat)
1. To perform or undergo infiltration. 2. SYN: infiltration (2) . 3. A cellular infiltration (1) in the lung as inferred from appearance of a localized, ill-defined opacity on a chest radiograph; commonly used to describe a shadow on a radiograph. [L. in + Mediev. L. filtro, pp. -atus, to strain through felt, fr. filtrum, felt] Assmann tuberculous i. SYN: infraclavicular i.. infraclavicular i. an incipient lesion of tuberculous infection. SYN: Assmann tuberculous i..

infiltration (in′fil-tra′shun)
1. The act of permeating or penetrating into a substance, cell, or tissue; said of gases, fluids, or matter held in solution. 2. The gas, fluid, or dissolved matter that has entered any substance, cell, or tissue. SYN: infiltrate (2) . 3. Injection of solution into tissues, as in i. anesthesia. 4. Extravasation of solutions intended for intravascular injection. adipose i. growth of normal adult fat cells in sites where they are not usually present. calcareous i. SYN: calcification. cellular i. migration of cells from their sources of origin, or direct extension of cells as a result of unusual growth and multiplication, thereby resulting in fairly well-defined foci, irregular accumulations, or diffusely distributed individual cells in the connective tissue and interstices of various organs and tissues; used especially with reference to such changes associated with inflammations and certain types of malignant neoplasms. epituberculous i. an i. superimposed upon a tuberculous lesion. fatty i. abnormal accumulation of fat droplets in the cytoplasm of cells, particularly of fat derived from outside the cells. SEE ALSO: fatty degeneration. gelatinous i. SYN: gray i.. gray i. a term sometimes used for the relatively rapidly formed, semisolid, gray or gray-white exudate (chiefly necrotic cells and remnants of tissue, and macrophages) resulting from unusually acute, overwhelming, diffuse tuberculous infection in the lung. SYN: gelatinous i.. lipomatous i. nonencapsulated adipose tissue forming a lipomalike mass, usually in the cardiac interatrial septum where it may cause arrhythmia and sudden death. SYN: lipomatous hypertrophy. paraneural i. SYN: perineural i.. perineural i. i. adjacent to or along a nerve. SYN: paraneural i..

infinity (in-fin′i-te)
SYN: infinite distance.

infirm (in-ferm′)
Weak or feeble because of old age or disease. [L. in-firmus, fr. in- neg. + firmus, strong]

infirmary (in-fer′ma-re)
A clinic or small hospital, especially in a school or college. [L. infirmarium; see infirm]

infirmity (in-fer′mi-te)
A weakness; an abnormal, more or less disabling, condition of mind or body. [see infirm]

inflammable (in-flam′a-bl)
SYN: flammable. [L. in-, intensive, + flamma, flame]

inflammation (in-fla-ma′shun)
A fundamental pathologic process consisting of a dynamic complex of cytologic and chemical reactions that occur in the affected blood vessels and adjacent tissues in response to an injury or abnormal stimulation caused by a physical, chemical, or biologic agent, including: 1) the local reactions and resulting morphologic changes, 2) the destruction or removal of the injurious material, 3) the responses that lead to repair and healing. The so-called “cardinal signs” of i. are: rubor, redness; calor, heat (or warmth); tumor, swelling; and dolor, pain; a fifth sign, functio laesa, inhibited or lost function, is sometimes added. All of the signs may be observed in certain instances, but no one of them is necessarily always present. [L. inflammo, pp. -atus, fr. in, in, + flamma, flame] active i. SYN: acute i.. acute i. any i. that has a fairly rapid onset, quickly becomes severe, and is usually manifested for only a few days, but which may persist for even a few weeks; characterized histologically by edema, hyperemia, and inflitrates of polymorphonuclear leukocytes. SYN: active i.. adhesive i. i. in which the amount of fibrin in the exudate is sufficient to result in a slight or moderate degree of adherence of adjacent tissues, as in healing by first intention. allergic i. allergic reaction. alterative i. a local reaction to injury, occasionally observed in the walls of blood vessels and in parenchymal cells of various organs in reacting to certain chemicals, viruses, and other intracellular agents; the response is characterized by degenerative changes in the cytoplasm and nucleus, frequently resulting in necrosis, but exudation (if any) is ordinarily observed only in the wall of the affected vessel, or in the interstices immediately adjacent to the affected vessel or parenchymal cells. SYN: degenerative i.. atrophic i. a form of chronic i. or repeated episodes of acute i. in which the continued or recurrent proliferation of fibroblasts results in the formation of fibrous tissue that eventually contracts and leads to compression and atrophy of parenchymal tissue. SYN: fibroid i.. catarrhal i. obsolete term for an inflammatory process that is most frequent in the respiratory tract, but may occur in any mucous membrane, and is characterized by hyperemia of the mucosal vessels, edema of the interstitial tissue, enlargement of the secretory epithelial cells (which proliferate and form conspicuous globules of mucus), and an irregular layer of viscous, mucinous material on the surface; as exudation progresses, variable numbers of neutrophils migrate into the affected tissue and are included in the exudate, along with fragments of degenerated and necrotic epithelial cells; such an i. may frequently become mucopurulent. chronic i. an i. that may begin with a relatively rapid onset or in a slow, insidious, and even unnoticed manner, and which tends to persist for several weeks, months, or years and has a vague and indefinite termination; occurs when the injuring agent (or products resulting from its presence) persists in the lesion, and the host's tissues respond in a manner (or to a degree) that is not sufficient to overcome completely the continuing effects of the injuring agent; characterized histopathologically by infiltrates of lymphocytes, plasma cells, and histiocytes; fibrosis; and granuloma formation. chronic active i. the coexistence of chronic i. and superimposed acute i.. degenerative i. SYN: alterative i.. exudative i. i. in which the conspicuous or distinguishing feature is an exudate, which may be chiefly serous, serofibrinous, fibrinous, or mucous ( e.g., relatively few cells are present), or may be characterized by relatively large numbers of neutrophils, eosinophils, lymphocytes, monocytes, or plasma cells, frequently with one or two types being predominant; it occurs not only as a separate and distinct pathologic process, but also frequently as a part of certain granulomatous inflammations. fibrinopurulent i. a purulent i. in which the exudate contains an unusually large amount of fibrin; also, a fibrinous or serofibrinous i. in which the accumulation of large numbers of polymorphonuclear leukocytes results in liquefactive necrosis of tissue and the formation of pus with a relatively large quantity of fibrin. fibrinous i. an exudative i. in which there is a disproportionately large amount of fibrin. fibroid i. SYN: atrophic i.. granulomatous i. a form of proliferative i. SEE ALSO: granuloma. hyperplastic i. SYN: proliferative i.. immune i. allergic reaction. interstitial i. i. in which the inflammatory reaction occurs chiefly in the supportive fibrous connective tissue or stroma of an organ. necrotic i., necrotizing i. usually an acute inflammatory reaction in which the predominant histologic change is fairly rapid necrosis that occurs diffusely or extensively in relatively large foci throughout the affected tissue, frequently with only little or no evidence of cells in the exudate. productive i. a vague term ordinarily used with reference to proliferative i., with or without an exudate; also sometimes used to indicate any i. in which grossly visible exudate is formed. proliferative i. an inflammatory reaction in which the distinguishing feature is an actual increase in the number of tissue cells, especially the reticuloendothelial macrophages, in contrast to cells exuded from blood vessels; in addition, exudates of various types are likely to be observed in granulomas and other forms of proliferative i., but the latter may occur without an exudate being formed (as in certain infections caused by virus). SYN: hyperplastic i.. pseudomembranous i. a form of exudative i. that involves mucous and serous membranes; relatively large quantities of fibrin in the exudate result in a rather tenacious membrane-like covering that is fairly adherent to the underlying acutely inflamed tissue; the pseudomembrane usually contains (in addition to the dense network of fibrin) varying quantities of plasma protein, degenerated and necrotic elements from the affected tissue, polymorphonuclear leukocytes, bacteria, etc. purulent i. an acute exudative i. in which the accumulation of polymorphonuclear leukocytes is sufficiently great that their enzymes cause liquefaction of the affected tissues, focally or diffusely; the purulent exudate is frequently termed pus, and consists of plasma and its constituents, end products of the enzymatic digestion of tissue, degenerated and necrotic cells and their debris, polymorphonuclear leukocytes and other white blood cells, the causal agent of the i., etc. SYN: suppurative i.. sclerosing i. i. leading to extensive formation of fibrous and scar tissue. serofibrinous i. i. in which the exudate consists chiefly of serous fluid with an unusually large proportion of fibrin. serous i. an exudative i. in which the exudate is predominantly fluid ( e.g., exuded from the blood vessels), with the protein, electrolytes, and other material contained therein; relatively few (if any) cells are observed. subacute i. an i. that is intermediate in duration between that of an acute i. and that of a chronic i., usually persisting longer than 3 or 4 weeks. suppurative i. SYN: purulent i..

inflammatory (in-flam′a-tor-e)
Pertaining to, characterized by, causing, resulting from, or becoming affected by inflammation.

inflation (in-fla′shun)
Distention by a fluid or gas. [L. inflatio, fr. in-flo, pp. -flatus, to blow into, inflate]

inflator (in-fla′ter, -tor)
An instrument for injecting air.

inflection, inflexion (in-flek′shun)
1. An inward bending. 2. Obsolete term for diffraction. [L. in-flecto, pp. -flexus, to bend]

influenza (in-floo-en′za)
An acute infectious respiratory disease, caused by i. viruses, which are in the family Orthomyxoviridae, in which the inhaled virus attacks the respiratory epithelial cells of susceptible persons and produces a catarrhal inflammation; characterized by sudden onset, chills, fever of short duration (3–4 days), severe prostration, headache, muscle aches, and a cough that usually is dry and may be followed by secondary bacterial infections that can last up to 10 days. The disease commonly occurs in epidemics, sometimes in pandemics, which develop quickly and spread rapidly; mortality rate is usually low, but may be high in cases with secondary bacterial pneumonia, particularly in the elderly and those with underlying debilitating diseases; strain-specific immunity develops, but mutations in the virus are frequent, and the immunity usually does not affect antigenically different strains. SYN: flu, grip (1) , grippe. [It. influence (of planets or stars), fr. L. influentia, fr. in-fluo, to flow in] i. A the most common type of i.. These strains have a high propensity for antigenic change resulting in mutations, partly because they can infect various animals where dual infections can occur, giving rise to new hybrid strains. The infections occur in epidemics, which may occur every 2–3 years and which vary in size and severity; perhaps the most important of the three types of i. (A, B, and C). Asian i. a worldwide i., apparently originating in China in the summer of 1957, which produces a milder disease than that of the pandemic of 1917–1919. i. B i. caused by strains of i. virus type B; outbreaks are usually more limited than those due to i. virus type A, although infections by the two types are clinically indistinguishable; occasionally associated with Reye syndrome. i. C i. caused by strains of type C i. virus; the disease is milder than that caused by types A and B and has become uncommon in recent years. endemic i. i., usually of a less severe type, occurring with some degree of regularity during the winter season, especially in the larger cities of the world. SYN: i. nostras. Hong Kong i. i. caused by a serotype of i. virus type A and first identified in Hong Kong in 1968. i. nostras SYN: endemic i.. Russian i. a pandemic of a strain i. A virus thought to have originated in Russia; occurred in 1978. Spanish i. i. that caused several waves of pandemic in 1918–1919, resulting in more than 20 million deaths worldwide; it was particularly severe in Spain (hence the name), but now is thought to have originated in the U.S. as a form of swine i.. swine i. an acute respiratory disease of swine caused by strains of i. virus type A; it is believed to have become adapted to swine in the United States during the great human pandemic in 1918; fatal cases, as in such cases of pandemic i. in humans, are commonly associated with secondary bacterial pneumonia.

influenzal (in-floo-en′zal)
Relating to, marked by, or resulting from influenza.

Influenza virus (in-floo-en′za-vi-rus)
The family of Orthomyxoviridae contains 3 genera: Influenzavirus A, B; Influenzavirus C; and “Thogoto-like viruses.” Each type of virus has a stable nucleoprotein group antigen common to all strains of the type, but distinct from that of the other type; the genome is negative sense single-stranded RNA in 6–8 segments; each also has a mosaic of surface antigens (hemagglutinin and neuraminidase) that characterize the strains and that are subject to variations of two kinds: 1) a rather continual drift that occurs independently within the hemagglutinin and neuraminidase antigens; 2) after a period of years, a sudden shift (notably in type A virus of human origin) to a different hemagglutinin or neuraminidase antigen. The sudden major shifts are the basis of subdivisions of type A virus of human origin, which occur following infection of the animal host with 2 different strains at the same time, resulting in a hybrid virus. Strain notations indicate type, geographic origin, year of isolation, and, in the case of type A strains, the characterizing subtypes of hemagglutinin and neuraminidase antigens ( e.g., A/Hong Kong/1/68 (H3 N2); B/Hong Kong/5/72).

infold (in-fold′)
To inclose within a fold, as in “infolding” an ulcer of the stomach, in which the walls on either side of the lesion are brought together and sutured.

informatics (in-for-mat′iks)
1. The study of information and ways to process and handle it, especially by means of information technology, i.e., computers and other electronic devices for rapid transfer, processing, and analysis of large amounts of data. 2. The science of arranging and organizing the product of genomic and functional genomic studies so that useful insight can result. SEE ALSO: bioinformatics. [information + -ics]

informed consent
Voluntary consent given by a person or a responsible proxy ( e.g., a parent) for participation in a study, immunization program, treatment regimen, invasive procedure, etc., after being informed of the purpose, methods, procedures, benefits, and risks. The essential criteria of i. are that the subject has both knowledge and comprehension, that consent is freely given without duress or undue influence, and that the right of withdrawal at any time is clearly communicated to the subject. Other aspects of i. in the context of epidemiologic and biomedical research, and criteria to be met in obtaining it, are specified in International Guidelines for Ethical Review of Epidemiologic Studies (Geneva: CIOMS/WHO 1991) and International Ethical Guidelines for Biomedical Research Involving Human Subjects (Geneva: CIOMS/WHO 1993).

informofers (in-for′mo-fers)
Name suggested for the protein particles that appear when RNA is removed from nucleoprotein particles. [information + -fer]

informosomes (in-for′mo-somz)
Name suggested for the bodies composed of messenger (informational) RNA and protein that are found in the cytoplasm of animal cells. [information + G. soma, body]

A position below the part denoted by the word to which it is joined. [L. below]

infraaxillary (in′fra-ak′si-lar-e)
SYN: subaxillary.

infrabulge (in′fra-bulj)
1. That portion of the crown of a tooth gingival to the height of contour. 2. That area of a tooth where the retentive portion of a clasp of a removable partial denture is placed.

infracardiac (in′fra-kar′de-ak)
Beneath the heart; below the level of the heart.

infracerebral (in′fra-ser′e-bral)
Pertaining to that portion of the nervous system below the level of the cerebrum.

infraclavicular (in′fra-kla-vik′u-lar)
SYN: subclavian (1) .

infraclusion (in-fra-kloo′zhun)
The state wherein a tooth has failed to erupt to the maxillomandibular plane of interdigitation. SYN: infraocclusion, infraversion (3) .

infracortical (in-fra-kor′ti-kal)
Beneath the cortex of an organ, mainly the brain or kidney. See subcortical.

infracostal (in-fra-kos′tal)
SYN: subcostal (1) .

infracotyloid (in-fra-kot′i-loyd)
Below the acetabulum or cotyloid cavity.

infracristal (in-fra-kris′tal)
Below the supraventricular crest of the right ventricle; usually used in reference to ventricular septal defect. [infra- + L. crista, crest]

infraction (in-frak′shun)
Obsolete term for fracture; especially one without displacement. [L. infractio, a breaking, fr. infringere, to break]

infradentale (in′fra-den-ta′le)
In craniometrics, the apex of the septum between the mandibular central incisors. SYN: lower alveolar point.

infradian (in-fra′de-an)
Relating to biologic variations or rhythms occurring in cycles less frequent than every 24 hours. Cf.:circadian, ultradian. [infra- + L. dies, day]

infradiaphragmatic (in′fra-di′a-frag-mat′ik)
SYN: subdiaphragmatic.

infraduction (in-fra-duk′shun)
SYN: deorsumduction.

infraglenoid (in′fra-gle′noyd)
Inferior to the glenoid cavity of the scapula. SYN: subglenoid.

infraglottic (in-fra-glot′ik)
Inferior to the glottis. SYN: subglottic.

infrahepatic (in-fra-he-pat′ik)
SYN: subhepatic.

infrahyoid (in′fra-hi′oyd)
Below the hyoid bone; denoting especially a group of muscles: the sternohyoideus, sternothyroideus, thyrohyoideus, and omohyoideus. SYN: subhyoid, subhyoidean.

inframamillary (in-fra-mam′i-lar-e)
Relating to that which is situated below a nipple.

inframammary (in-fra-mam′a-re)
Inferior to the mammary gland. SYN: submammary (2) .

inframandibular (in-fra-man-dib′u-lar)
SYN: submandibular.

inframarginal (in-fra-mar′ji-nal)
Below any margin or edge.

inframaxillary (in-fra-mak′si-la-re)
SYN: mandibular.

infranatant (in′fra-na′tant)
1. See i. fluid. 2. Lying below. [infra- + L. natare, to swim]

infraocclusion (in′fra-o-kloo′zhun)
SYN: infraclusion.


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