Infection control

From WikiMD's Health & Wellness Encyclopedia


Measures practiced by healthcare personnel in healthcare facilities to decrease transmission and acquisition of infectious agents (e.g., proper hand hygiene, scrupulous work practices, use of personal protective equipment (PPE) [masks or respirators, gloves, gowns, and eye protection]; infection control measures are based on how an infectious agent is transmitted and include standard, contact, droplet, and airborne precautions.

Glossary

  • Acceptable indoor air quality - Air in which there are no known contaminants at harmful concentrations as determined by knowledgeble authorities and with which a substantial majority (≥80%) of the people exposed do not express dissatisfaction.
  • ACGIH - American Conference of Governmental Industrial Hygienists.
  • Action level - The concentration of a contaminant at which steps should be taken to interrupt the trend toward higher, unacceptable levels.
  • Aerosol - Particles of respirable size generated by both humans and environmental sources and that have the capability of remaining viable and airborne for extended periods in the indoor environment.
  • AIA - American Institute of Architects, a professional group responsible for publishing the Guidelines for Design and Construction of Hospitals and Healthcare Facilities, a consensus document for design and construction of health-care facilities endorsed by the U.S. Department of Health and Human Services, health-care professionals, and professional organizations.
  • Air changes per hour (ACH) - The ratio of the volume of air flowing through a space in a certain period of time (the airflow rate) to the volume of that space (the room volume). This ratio is expressed as the number of air changes per hour (ACH).
  • Air mixing - The degree to which air supplied to a room mixes with the air already in the room, usually expressed as a mixing factor. This factor varies from 1 (for perfect mixing) to 10 (for poor mixing). It is used as a multiplier to determine the actual airflow required (i.e., the recommended ACH multiplied by the mixing factor equals the actual ACH required).
  • Airborne transmission - A means of spreading infection when airborne droplet nuclei (small particle residue of evaporated droplets ≤5 μm in size containing microorganisms that remain suspended in air for long periods of time) are inhaled by the susceptible host.
  • Air-cleaning system - A device or combination of devices applied to reduce the concentration of airborne contaminants (e.g., microorganisms, dusts, fumes, aerosols, other particulate matter, and gases).
  • Air conditioning - The process of treating air to meet the requirements of a conditioned space by controlling its temperature, humidity, cleanliness, and distribution.
  • Allogeneic - Non-twin, non-self. The term refers to transplanted tissue from a donor closely matched to a recipient but not related to that person.
  • Anemometer - A flow meter which measures the wind force and velocity of air. An anemometer is often used as a means of determining the volume of air being drawn into an air sampler.
  • Anteroom - A small room leading from a corridor into an isolation room. This room can act as an airlock, preventing the escape of contaminants from the isolation room into the corridor.
  • ASHE - American Society for Healthcare Engineering, an association affiliated with the American Hospital Association.
  • ASHRAE - American Society of Heating, Refrigerating, and Air-Conditioning Engineers Inc.
  • Autologous self - The term refers to transplanted tissue whose source is the same as the recipient, or an identical twin.
  • Automated cycler - A machine used during peritoneal dialysis which pumps fluid into and out of the patient while he/she sleeps.
  • Biochemical oxygen demand (BOD) - A measure of the amount of oxygen removed from aquatic environments by aerobic microorganisms for their metabolic requirements. Measurement of BOD is used to determine the level of organic pollution of a stream or lake. The greater the BOD, the greater the degree of water pollution. The term is also referred to as Biological Oxygen Demand (BOD).
  • Biological oxygen demand (BOD) - An indirect measure of the concentration of biologically degradable material present in organic wastes (pertaining to water quality). It usually reflects the amount of oxygen consumed in five days by biological processes breaking down organic waste (BOD5).
  • Biosafety level - A combination of microbiological practices, laboratory facilities, and safety equipment determined to be sufficient to reduce or prevent occupational exposures of laboratory personnel to the microbiological agents they work with. There are four biosafety levels based on the hazards associated with the various microbiological agents.
  • BOD5 - The amount of dissolved oxygen consumed in five days by biological processes breaking down organic matter.
  • Bonneting - A floor cleaning method for either carpeted or hard surface floors that uses a circular motion of a large fibrous disc to lift and remove soil and dust from the surface.
  • Capped spur - A pipe leading from the water recirculating system to an outlet that has been closed off (“capped”). A capped spur cannot be flushed, and it might not be noticed unless the surrounding wall is removed.
  • CFU/m3 - Colony forming units per cubic meter (of air).
  • Chlamydospores - Thick-walled, typically spherical or ovoid resting spores asexually produced by certain types of fungi from cells of the somatic hyphae.
  • Chloramines - Compounds containing nitrogen, hydrogen, and chlorine. These are formed by the reaction between hypochlorous acid (HOCl) and ammonia (NH3) and/or organic amines in water. The formation of chloramines in drinking water treatment extends the disinfecting power of chlorine. The term is also referred to as Combined Available Chlorine.
  • Cleaning - The removal of visible soil and organic contamination from a device or surface, using either the physical action of scrubbing with a surfactant or detergent and water, or an energy-based process (e.g., ultrasonic cleaners) with appropriate chemical agents.
  • Coagulation-flocculation - Coagulation is the clumping of particles that results in the settling of impurities. It may be induced by coagulants (e.g., lime, alum, and iron salts). Flocculation in water and wastewater treatment is the agglomeration or clustering of colloidal and finely-divided suspended matter after coagulation by gentle stirring by either mechanical or hydraulic means, such that they can be separated from water or sewage.
  • Commissioning (a room) - Testing a system or device to ensure that it meets the pre-use specifications as indicated by the manufacturer or predetermined standard, or air sampling in a room to establish a preoccupancy baseline standard of microbial or particulate contamination. The term is also referred to as benchmarking at 77°F (25°C).
  • Conidia - Asexual spores of fungi borne externally.
  • Conditioned space - That part of a building that is heated or cooled, or both, for the comfort of the occupants.
  • Contaminant - An unwanted airborne constituent that may reduce the acceptibility of air.
  • Convection - The transfer of heat or other atmospheric properties within the atmosphere or in the airspace of an enclosure by the circulation of currents from one region to another, especially by such motion directed upward.
  • Cooling tower - A structure engineered to receive accumulated heat from ventilation systems and equipment and transfer this heat to water, which then releases the stored heat to the atmosphere through evaporative cooling.
  • Critical item (medical instrument) - A medical instrument or device that contacts normally sterile areas of the body or enters the vascular system. There is a high risk of infection from such devices if they are microbiologically contaminated prior to use. These devices must be sterilized before use.
  • Dead legs - Areas in the water system where water stagnates. A dead leg is a pipe or spur, leading from the water recirculating system to an outlet that is used infrequently, resulting in inadequate flow of water from the recirculating system to the outlet. This inadequate flow reduces the perfusion of heat or chlorine into this part of the water distribution system, thereby adversely affecting the disinfection of the water system in that area.
  • Deionization - Removal of ions from water by exchange with other ions associated with fixed charges on a resin bed. Cations are usually removed and H+ ions are exchanged; OH– ions are exchanged for anions.
  • Detritis - Particulate matter produced by or remaining after the wearing away or disintegration of a substance or tissue.
  • Dew point - The temperature at which a gas or vapor condenses to form a liquid; the point at which moisture begins to condense out of the air. At dew point, air is cooled to the point where it is at 100% relative humidity or saturation.
  • Dialysate - The aqueous electrolyte solution, usually containing dextrose, used to make a concentration gradient between the solution and blood in the hemodialyzer (dialyzer).
  • Dialyzer - A device that consists of two compartments (blood and dialysate) separated by a semipermeable membrane. A dialyzer is usually referred to as an artificial kidney.
  • Diffuser - The grille plate that disperses the air stream coming into the conditioned air space.
  • Direct transmission - Involves direct body surface-to-body surface contact and physical transfer of microorganisms between a susceptible host and an infected/colonized person, or exposure to cloud of infectious particles within 3 feet of the source; the aerosolized particles are >5 μm in size.
  • Disability - As defined by the Americans with Disabilities Act, a disability is any physical or mental impairment that substantially limits one or more major life activities, including but not limited to walking, talking, seeing, breathing, hearing, or caring for oneself.
  • Disinfection - A generally less lethal process of microbial inactivation (compared to sterilization) that eliminates virtually all recognized pathogenic microorganisms but not necessarily all microbial forms (e.g., bacterial spores).
  • Drain pans - Pans that collect water within the HVAC system and remove it from the system. Condensation results when air and steam come together.
  • Drift - Circulating water lost from the cooling tower in the form as liquid droplets entrained in the exhaust air stream (i.e., exhaust aerosols from a cooling tower).
  • Drift eliminators - An assembly of baffles or labyrinth passages through which the air passes prior to its exit from the cooling tower. The purpose of a drift eliminator is to remove entrained water droplets from the exhaust air.
  • Droplets - Particles of moisture, such as are generated when a person coughs or sneezes, or when water is converted to a fine mist by a device such as an aerator or shower head. These particles may contain infectious microorganisms. Intermediate in size between drops and droplet nuclei, these particles tend to quickly settle out from the air so that any risk of disease transmission is generally limited to persons in close proximity to the droplet source.
  • Droplet nuclei - Sufficiently small particles (1–5 μm in diameter) that can remain airborne indefinitely and cause infection when a susceptible person is exposed at or beyond 3 feet of the source of these particles.
  • Dual duct system - An HVAC system that consists of parallel ducts that produce a cold air stream in one and a hot air stream in the other.
  • Dust - An air suspension of particles (aerosol) of any solid material, usually with particle sizes ≤100 μm in diameter.
  • Dust-spot test - A procedure that uses atmospheric air or a defined dust to measure a filter’s ability to remove particles. A photometer is used to measure air samples on either side of the filter, and the difference is expressed as a percentage of particles removed.
  • Effective leakage area - The area through which air can enter or leave the room. This does not include supply, return, or exhaust ducts. The smaller the effective leakage area, the better isolated the room.
  • Endotoxin - The lipopolysaccharides of gram-negative bacteria, the toxic character of which resides in the lipid portion. Endotoxins generally produce pyrogenic reactions in persons exposed to these bacterial components.
  • Enveloped virus - A virus whose outer surface is derived from a membrane of the host cell (either nuclear or the cell’s outer membrane) during the budding phase of the maturation process. This membrane-derived material contains lipid, a component that makes these viruses sensitive to the action of chemical germicides.
  • Evaporative condenser - A wet-type, heat-rejection unit that produces large volumes of aerosols during the process of removing heat from conditioned space air.
  • Exhaust air - Air removed from a space and not reused therein.
  • Exposure - The condition of being subjected to something (e.g., infectious agents) that could have a harmful effect.


  • Fastidious - Having complex nutritional requirements for growth, as in microorganisms.
  • Fill - That portion of a cooling tower which makes up its primary heat transfer surface. Fill is alternatively known as “packing.”
  • Fixed room-air HEPA recirculation systems - Nonmobile devices or systems that remove airborne contaminants by recirculating air through a HEPA filter. These may be built into the room and permanently ducted or may be mounted to the wall or ceiling within the room. In either situation, they are fixed in place and are not easily movable.
  • Fomite - An inanimate object that may be contaminated with microorganisms and serves in their transmission.
  • Free and available chlorine - The term applied to the three forms of chlorine that may be found in solution (i.e., chlorine [Cl2], hypochlorite [OCl–], and hypochlorous acid [HOCl]).
  • Germicide - A chemical that destroys microorganisms. Germicides may be used to inactivate microorganisms in or on living tissue (antiseptics) or on environmental surfaces (disinfectants).
  • Health-care associated - An outcome, usually an infection, that occurs in any health-care facility as a result of medical care. The term “health-care associated” replaces “nosocomial,” the latter term being limited to adverse infectious outcomes occurring only in hospitals.
  • Hemodiafiltration - A form of renal replacement therapy in which waste solutes in the patient’s blood are removed by both diffusion and convection through a high-flux membrane.
  • Hemodialysis - A treatment for renal replacement therapy in which waste solutes in the patient’s blood are removed by diffusion and/or convection through the semipermeable membrane of an artificial kidney or dialyzer.
  • Hemofiltration - Cleansing of waste products or other toxins from the blood by convection across a semipermeable, high-flux membrane where fluid balance is maintained by infusion of sterile, pyrogenfree substitution fluid pre- or post-hemodialyzer.
  • HEPA filter - High Efficiency Particulate Air filters capable of removing 99.97% of particles 0.3 μm in diameter and may assist in controlling the transmission of airborne disease agents. These filters may be used in ventilation systems to remove particles from the air or in personal respirators to filter air before it is inhaled by the person wearing the respirator. The use of HEPA filters in ventilation systems requires expertise in installation and maintenance. To test this type of filter, 0.3 μm particles of dioctylphthalate (DOP) are drawn through the filter. Efficiency is calculated by comparing the downstream and upstream particle counts. The optimal HEPA filter allows only three particles to pass through for every 10,000 particles that are fed to the filter.
  • Heterotrophic (heterotroph) - That which requires some nutrient components from exogenous sources. Heterotrophic bacteria cannot synthesize all of their metabolites and therefore require certain nutrients from other sources.
  • High flux - A type of dialyzer or hemodialysis treatment in which large molecules (>8,000 daltons [e.g., β2 microglobulin]) are removed from blood.
  • High-level disinfection - A disinfection process that inactivates vegetative bacteria, mycobacteria, fungi, and viruses, but not necessarily high numbers of bacterial spores.
  • Housekeeping surfaces - Environmental surfaces (e.g., floors, walls, ceilings, and tabletops) that are not involved in direct delivery of patient care in health-care facilities.
  • Hoyer lift - An apparatus that facilitates the repositioning of the non-ambulatory patient from bed to wheelchair or gurney and subsequently to therapy equipment (immersion tanks).
  • Hubbard tank - A tank used in hydrotherapy that may accomodate whole-body immersion (e.g., as may be indicated for burn therapy). Use of a Hubbard tank has been replaced largely by bedside post-lavage therapy for wound care management.
  • HVAC - Heating, Ventilation, Air Conditioning.
  • Iatrogenic - Induced in a patient by a physician’s activity, manner, or therapy. The term is used especially in reference to an infectious complication or other adverse outcome of medical treatment.
  • Impactor - An air-sampling device in which particles and microorganisms are directed onto a solid surface and retained there for assay.
  • Impingement - An air-sampling method during which particles and microorganisms are directed into a liquid and retained there for assay.
  • Indirect transmission - Involves contact of a susceptible host with a contaminated intermediate object, usually inanimate (a fomite).
  • Induction unit - The terminal unit of an in-room ventilation system. Induction units take centrally conditioned air and further moderate its temperature. Induction units are not appropriate for areas with high exhaust requirements (e.g., research laboratories).
  • Intermediate-level disinfection - A disinfection process that inactivates vegetative bacteria, most fungi, mycobacteria, and most viruses (particularly the enveloped viruses), but does not inactivate bacterial spores.
  • Isoform - A possible configuration (tertiary structure) of a protein molecule. With respect to prion proteins, the molecules with large amounts of α-conformation are the normal isoform of that particular protein, whereas those prions with large amounts of β-sheet conformation are the proteins associated with the development of spongiform encephalopathy (e.g., Creutzfeldt-Jakob disease [CJD]).
  • Laminar flow - HEPA-filtered air that is blown into a room at a rate of 90 ± 10 feet/min in a unidirectional pattern with 100 ACH–400 ACH.
  • Large enveloped virus - Viruses whose particle diameter is >50 nm and whose outer surface is covered by a lipid-containing structure derived from the membranes of the host cells. Examples of large enveloped viruses include influenza viruses, herpes simplex viruses, and poxviruses.
  • Laser plume - The transfer of electromagnetic energy into tissues which results in a release of particles, gases, and tissue debris.
  • Lipid-containing viruses - Viruses whose particle contains lipid components. The term is generally synonymous with enveloped viruses whose outer surface is derived from host cell membranes. Lipid-containing viruses are sensitive to the inactivating effects of liquid chemical germicides.
  • Lithotriptors - Instruments used for crushing caliculi (i.e., calcified stones, and sand) in the bladder or kidneys.
  • Low efficiency filter - The prefilter with a particle-removal efficiency of approximately 30% through which incoming air first passes. See also Prefilter.
  • Low-level disinfection - A disinfection process that will inactivate most vegetative bacteria, some fungi, and some viruses, but cannot be relied upon to inactivate resistant microorganisms (e.g., mycobacteria or bacterial spores).
  • Makeup air - Outdoor air supplied to the ventilation system to replace exhaust air.
  • Makeup water - A cold water supply source for a cooling tower.
  • Manometer - A device that measures the pressure of liquids and gases. A manometer is used to verify air filter performance by measuring pressure differentials on either side of the filter.
  • Membrane filtration - An assay method suitable for recovery and enumeration of microorganisms from liquid samples. This method is used when sample volume is large and anticipated microbial contamination levels are low.
  • Mesophilic - That which favors a moderate temperature. For mesophilic bacteria, a temperature range of 68°F–131°F (20°C–55°C) is favorable for their growth and proliferation.
  • Mixing box - The site where the cold and hot air streams mix in the HVAC system, usually situated close to the air outlet for the room.
  • Mixing faucet - A faucet that mixes hot and cold water to produce water at a desired temperature.
  • MMAD - Mass Median Aerodynamic Diameter. This is the unit used by ACGIH to describe the size of particles when particulate air sampling is conducted.
  • Moniliaceous - Hyaline or brightly colored. This is a laboratory term for the distinctive characteristics of certain opportunistic fungi in culture (e.g., Aspergillus spp. and Fusarium spp.).
  • Monochloramine - The result of the reaction between chlorine and ammonia that contains only one chlorine atom. Monochloramine is used by municipal water systems as a water treatment.
  • Natural ventilation - The movement of outdoor air into a space through intentionally provided openings (i.e., windows, doors, or nonpowered ventilators).
  • Negative pressure - Air pressure differential between two adjacent airspaces such that air flow is directed into the room relative to the corridor ventilation (i.e., room air is prevented from flowing out of the room and into adjacent areas).
  • Neutropenia - A medical condition in which the patient’s concentration of neutrophils is substantially less than that in the normal range. Severe neutropenia occurs when the concentration is <1,000 polymorphonuclear cells/μL for 2 weeks or <100 polymorphonuclear cells /mL for 1 week, particularly for hematopoietic stem cell transplant (HSCT) recipients.
  • Noncritical devices - Medical devices or surfaces that come into contact with only intact skin. The risk of infection from use of these devices is low.
  • Non-enveloped virus - A virus whose particle is not covered by a structure derived from a membrane of the host cell. Non-enveloped viruses have little or no lipid compounds in their biochemical composition, a characteristic that is significant to their inherent resistance to the action of chemical germicides.
  • Nosocomial - An occurrence, usually an infection, that is acquired in a hospital as a result of medical care.
  • NTM - Nontuberculous mycobacteria. These organisms are also known as atypical mycobacteria, or as “Mycobacteria other than tuberculosis” (MOTT). This descriptive term refers to any of the fast- or slow-growing Mycobacterium spp. found in primarily in natural or man-made waters, but it excludes Mycobacterium tuberculosis and its variants.
  • Nuisance dust - Generally innocuous dust, not recognized as the direct cause of serious pathological conditions.
  • Oocysts - A cyst in which sporozoites are formed; a reproductive aspect of the life cycle of a number of parasitic agents (e.g., Cryptosporidium spp., and Cyclospora spp.).
  • Outdoor air - Air taken from the external atmosphere and, therefore, not previously circulated through the ventilation system.
  • Parallel streamlines - A unidirectional airflow pattern achieved in a laminar flow setting, characterized by little or no mixing of air.
  • Particulate matter (particles) - A state of matter in which solid or liquid substances exist in the form of aggregated molecules or particles. Airborne particulate matter is typically in the size range of 0.01–100 μm diameter.
  • Pasteurization - A disinfecting method for liquids during which the liquids are heated to 140°F (60°C) for a short time (≥30 mins.) to significantly reduce the numbers of pathogenic or spoilage microorganisms.
  • Plinth - A treatment table or a piece of equipment used to reposition the patient for treatment.
  • Positive pressure - Air pressure differential between two adjacent air spaces such that air flow is directed from the room relative to the corridor ventilation (i.e., air from corridors and adjacent areas is prevented from entering the room).
  • Potable (drinking) water - Water that is fit to drink. The microbiological quality of this water as defined by EPA microbiological standards from the Surface Water Treatment Rule:

Giardia lamblia: 99.9% killed/inactivated

viruses: 99.9% inactivated;

Legionella spp.: no limit, but if Giardia and viruses are inactivated, Legionella will also be controlled;

heterotrophic plate count [HPC]: ≤500 CFU/mL; and

>5% of water samples total coliform-positive in a month.

  • PPE - Personal Protective Equipment.
  • ppm - Parts per million. The term is a measure of concentration in solution. Chlorine bleaches (undiluted) that are available in the U.S. (5.25%–6.15% sodium hypochlorite) contain approximately 50,000–61,500 parts per million of free and available chlorine.
  • Prefilter - The first filter for incoming fresh air in a HVAC system. This filter is approximately 30% efficient in removing particles from the air. See also Low-Efficiency Filter.
  • Prion - A class of agent associated with the transmission of diseases knowns as transmissible spongiform encephalopathies (TSEs). Prions are considered to consist of protein only, and the abnormal isoform of this protein is thought to be the agent that causes diseases such as Creutzfeldt-Jakob disease (CJD), kuru, scrapie, bovine spongiform encephalopathy (BSE), and the human version of BSE which is variant CJD (vCJD).
  • Product water - Water produced by a water treatment system or individual component of that system.
  • Protective environment - A special care area, usually in a hospital, designed to prevent transmission of opportunistic airborne pathogens to severely immunosuppressed patients.
  • Pseudoepidemic (pseudo-outbreak) - A cluster of positive microbiologic cultures in the absence of clinical disease. A pseudoepidemic usually results from contamination of the laboratory apparatus and process used to recover microorganisms.
  • Pyrogenic - An endotoxin burden such that a patient would receive ≥5 endotoxin units (EU) per kilogram of body weight per hour, thereby causing a febrile response. In dialysis this usually refers to water or dialysate having endotoxin concentrations of ≥5 EU/mL.
  • Rank order - A strategy for assessing overall indoor air quality and filter performance by comparing airborne particle counts from lowest to highest (i.e., from the best filtered air spaces to those with the least filtration).
  • RAPD - A method of genotyping microorganisms by randomly amplified polymorphic DNA. This is one version of the polymerase chain reaction method.
  • Recirculated air - Air removed from the conditioned space and intended for reuse as supply air.
  • Relative humidity - The ratio of the amount of water vapor in the atmosphere to the amount necessary for saturation at the same temperature. Relative humidity is expressed in terms of percent and measures the percentage of saturation. At 100% relative humidity, the air is saturated. The relative humidity decreases when the temperature is increased without changing the amount of moisture in the air.
  • Reprocessing (of medical instruments) - The procedures or steps taken to make a medical instrument safe for use on the next patient. Reprocessing encompasses both cleaning and the final or terminal step (i.e., sterilization or disinfection) which is determined by the intended use of the instrument according to the Spaulding classification.
  • Residuals - The presence and concentration of a chemical in media (e.g., water) or on a surface after the chemical has been added.
  • Reservoir - A nonclinical source of infection.
  • Respirable particles - Those particles that penetrate into and are deposited in the nonciliated portion of the lung. Particles >10 μm in diameter are not respirable.
  • Return air - Air removed from a space to be then recirculated.
  • Reverse osmosis (RO) - An advanced method of water or wastewater treatment that relies on a semipermeable membrane to separate waters from pollutants. An external force is used to reverse the normal osmotic process resulting in the solvent moving from a solution of higher concentration to one of lower concentration.
  • Riser - Water piping that connects the circulating water supply line, from the level of the base of the tower or supply header, to the tower’s distribution system.
  • RODAC - Replicate Organism Direct Agar Contact. This term refers to a nutrient agar plate whose convex agar surface is directly pressed onto an environmental surface for the purpose of microbiologic sampling of that surface.
  • Routine sampling - Environmental sampling conducted without a specific, intended purpose and with no action plan dependent on the results obtained.
  • Sanitizer - An agent that reduces microbial contamination to safe levels as judged by public health standards or requirements.
  • Saprophytic - A naturally-occurring microbial contaminant.
  • Sedimentation - The act or process of depositing sediment from suspension in water. The term also refers to the process whereby solids settle out of wastewater by gravity during treatment.
  • Semicritical devices - Medical devices that come into contact with mucous membranes or non-intact skin.
  • Service animal - Any animal individually trained to do work or perform tasks for the benefit of a person with a disability.
  • Shedding - The generation and dispersion of particles and spores by sources within the patient area, through activities such as patient movement and airflow over surfaces.
  • Small, non-enveloped viruses - Viruses whose particle diameter is <50 nm and whose outer surface is the protein of the particle itself and not that of host cell membrane components. Examples of small, non-enveloped viruses are polioviruses and hepatitis A virus.
  • Spaulding Classification - The categorization of inanimate medical device surfaces in the medical environment as proposed in 1972 by Dr. Earle Spaulding. Surfaces are divided into three general categories, based on the theoretical risk of infection if the surfaces are contaminated at time of use. The categories are “critical,” “semicritical,” and “noncritical.”
  • Specific humidity - The mass of water vapor per unit mass of moist air. It is expressed as grains of water per pound of dry air, or pounds of water per pound of dry air. The specific humidity changes as moisture is added or removed. However, temperature changes do not change the specific humidity unless the air is cooled below the dew point.
  • Splatter - Visible drops of liquid or body fluid that are expelled forcibly into the air and settle out quickly, as distinguished from particles of an aerosol which remain airborne indefinitely.
  • Sterilization - The use of a physical or chemical procedure to destroy all microbial life, including large numbers of highly-resistant bacterial endospores.
  • Stop valve - A valve that regulates the flow of fluid through a pipe. The term may also refer to a faucet.
  • Substitution fluid - Fluid that is used for fluid management of patients receiving hemodiafiltration. This fluid can be prepared on-line at the machine through a series of ultrafilters or with the use of sterile peritoneal dialysis fluid.
  • Supply air - Air that is delivered to the conditioned space and used for ventilation, heating, cooling, humidification, or dehumidification.
  • Tensile strength - The resistance of a material to a force tending to tear it apart, measured as the maximum tension the material can withstand without tearing.
  • Therapy animal - An animal (usually a personal pet) that, with their owners or handlers, provide supervised, goal-directed intervention to clients in hospitals, nursing homes, special-population schools, and other treatment sites.
  • Thermophilic - Capable of growing in environments warmer than body temperature.
  • TLV® - An exposure level under which most people can work consistently for 8 hours a day, day after day, without adverse effects. The term is used by the ACGIH to designate degree of exposure to contaminants. TLV® can be expressed as approximate milligrams of particulate per cubic meter of air (mg/m3). TLVs® are listed as either an 8-hour TWA (time weighted average) or a 15-minute STEL (short term exposure limit).
  • TLV-TWA - Threshold Limit Value-Time Weighted Average. The term refers to the time-weighted average concentration for a normal 8-hour workday and a 40-hour workweek to which nearly all workers may be exposed repeatedly, day after day, without adverse effects. The TLV-TWA for “particulates (insoluble) not otherwise classified” (PNOC) – (sometimes referred to as nuisance dust) – are those particulates containing no asbestos and <1% crystalline silica. A TLV-TWA of 10 mg/m3 for inhalable particulates and a TLV-TWA of 3 mg/m3 for respirable particulates (particulates ≤5 μm in aerodynamic diameter) have been established.
  • Transient - A change in the condition of the steady state that takes a very short time compared with the steady state. Opening a door, and shaking bed linens are examples of transient activities.
  • TWA - Average exposure for an individual over a given working period, as determined by sampling at given times during the period. TWA is usually presented as the average concentration over an 8-hour workday for a 40-hour workweek.
  • Ultraclean air - Air in laminar flow ventilation that has also passed through a bank of HEPA filters.
  • Ultrafilter - A membrane filter with a pore size in the range of 0.001–0.05 μm, the performance of which is usually rated in terms of a nominal molecular weight cut-off (defined as the smallest molecular weight species for which the filter membrance has more than 90% rejection).
  • Ultrafiltered dialysate - The process by which dialysate is passed through a filter having a molecular weight cut-off of approximately 1 kilodalton for the purpose of removing bacteria and endotoxin from the bath.
  • Ultraviolet germicidal irradiation lamps - Lamps that kill or inactivate microorganisms by emitting ultraviolet germicidal radiation, predominantly at a wavelength of 254 nm. UVGI lamps can be used in ceiling or wall fixtures or within air ducts of ventilation systems.
  • Vapor pressure - The pressure exerted by free molecules at the surface of a solid or liquid. Vapor pressure is a function of temperature, increasing as the temperature rises.
  • Vegetative bacteria - Bacteria that are actively growing and metabolizing, as opposed to a bacterial state of quiescence that is achieved when certain bacteria (gram-positive bacilli) convert to spores when the environment can no longer support active growth.
  • Vehicle - Any object, person, surface, fomite, or media that may carry and transfer infectious microorganisms from one site to another.
  • Ventilation - The process of supplying and removing air by natural or mechanical means to and from any space. Such air may or may not be conditioned.
  • Ventilation air - That portion of the supply air consisting of outdoor air plus any recirculated air that has been treated for the purpose of maintaining acceptable indoor air quality.
  • Ventilation, dilution - An engineering control technique to dilute and remove airborne contaminants by the flow of air into and out of an area. Air that contains droplet nuclei is removed and replaced by contaminant-free air. If the flow is sufficient, droplet nuclei become dispersed, and their concentration in the air is diminished.
  • Ventilation, local exhaust - Ventilation used to capture and removed airborne contaminants by enclosing the contaminant source (the patient) or by placing an exhaust hood close to the contaminant source.
  • v/v - Volume to volume. This term is an expression of concentration of a percentage solution when the principle component is added as a liquid to the diluent.
  • w/v - Weight to volume. This term is an expression of concentration of a percentage solution when the principle component is added as a solid to the diluent.
  • Weight-arrestance - A measure of filter efficiency, used primarily when describing the performance of low- and medium-efficiency filters. The measurement of weight-arrestance is performed by feeding a standardized synthetic dust to the filter and weighing the fraction of the dust removed.
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