Normal human body temperature, also known as normothermia or euthermia, is the typical temperature range found in humans. The normal human body temperature range is typically stated as 36.5–37.5 °C (97.7–99.5 °F).
Individual body temperature depends upon the age, exertion, infection, sex, and reproductive status of the subject, the time of day, the place in the body at which the measurement is made, and the subject's state of consciousness (waking, sleeping or sedated), activity level, and emotional state. It is typically maintained within this range by thermoregulation.
Temperature control (thermoregulation) is part of a homeostatic mechanism that keeps the organism at optimum operating temperature, as the temperature affects the rate of chemical reactions. In humans, the average internal temperature is 37.0 °C (98.6 °F), though it varies among individuals. However, no person always has exactly the same temperature at every moment of the day. Temperatures cycle regularly up and down through the day, as controlled by the person's circadian rhythm. The lowest temperature occurs about two hours before the person normally wakes up. Additionally, temperatures change according to activities and external factors.
In addition to varying throughout the day, normal body temperature may also differ as much as 0.5 °C (0.9 °F) from one day to the next, so that the highest or lowest temperatures on one day will not always exactly match the highest or lowest temperatures on the next day.
Normal human body temperature varies slightly from person to person and by the time of day. Consequently, each type of measurement has a range of normal temperatures. The range for normal human body temperatures, taken orally, is 36.8±0.5 °C (98.2±0.9 °F). This means that any oral temperature between 36.3 and 37.3 °C (97.3 and 99.1 °F) is likely to be normal.
The normal human body temperature is often stated as 36.5–37.5 °C (97.7–99.5 °F). In adults a review of the literature has found a wider range of 33.2–38.2 °C (91.8–100.8 °F) for normal temperatures, depending on the gender and location measured.
Reported values vary depending on how it is measured: oral (under the tongue): 36.8±0.4 °C (98.2±0.72 °F), internal (rectal, vaginal): 37.0 °C (98.6 °F). A rectal or vaginal measurement taken directly inside the body cavity is typically slightly higher than oral measurement, and oral measurement is somewhat higher than skin measurement. Other places, such as under the arm or in the ear, produce different typical temperatures. While some people think of these averages as representing normal or ideal measurements, a wide range of temperatures has been found in healthy people. The body temperature of a healthy person varies during the day by about 0.5 °C (0.9 °F) with lower temperatures in the morning and higher temperatures in the late afternoon and evening, as the body's needs and activities change. Other circumstances also affect the body's temperature. The core body temperature of an individual tends to have the lowest value in the second half of the sleep cycle; the lowest point, called the nadir, is one of the primary markers for circadian rhythms. The body temperature also changes when a person is hungry, sleepy, sick, or cold.
Body temperature normally fluctuates over the day following Circadian rhythms, with the lowest levels around 4 a.m. and the highest in the late afternoon, between 4:00 and 6:00 p.m. (assuming the person sleeps at night and stays awake during the day). Therefore, an oral temperature of 37.3 °C (99.1 °F) would, strictly speaking, be a normal, healthy temperature in the afternoon but not in the early morning. An individual's body temperature typically changes by about 0.5 °C (0.9 °F) between its highest and lowest points each day.
Body temperature is sensitive to many hormones, so women have a temperature rhythm that varies with the menstrual cycle, called a circamensal rhythm. A woman's basal body temperature rises sharply after ovulation, as estrogen production decreases and progesterone increases. Fertility awareness programs use this change to identify when a woman has ovulated in order to achieve or avoid pregnancy. During the luteal phase of the menstrual cycle, both the lowest and the average temperatures are slightly higher than during other parts of the cycle. However, the amount that the temperature rises during each day is slightly lower than typical, so the highest temperature of the day is not very much higher than usual. Hormonal contraceptives both suppress the circamensal rhythm and raise the typical body temperature by about 0.6 °C (1.1 °F).
Temperature also varies with the change of seasons during each year. This pattern is called a circannual rhythm. Studies of seasonal variations have produced inconsistent results. People living in different climates may have different seasonal patterns.
Increased physical fitness increases the amount of daily variation in temperature.
With increased age, both average body temperature and the amount of daily variability in the body temperature tend to decrease. Elderly patients may have a decreased ability to generate body heat during a fever, so even a somewhat elevated temperature can indicate a serious underlying cause in geriatrics.
|Oral||33.2–38.1 °C (91.8–100.6 °F)||35.7–37.7 °C (96.3–99.9 °F)|
|Rectal||36.8–37.1 °C (98.2–98.8 °F)||36.7–37.5 °C (98.1–99.5 °F)|
|Tympanic||35.7–37.5 °C (96.3–99.5 °F)||35.5–37.5 °C (95.9–99.5 °F)|
Different methods used for measuring temperature produce different results. The temperature reading depends on which part of the body is being measured. The typical daytime temperatures among healthy adults are as follows:
Generally, oral, rectal, gut, and core body temperatures, although slightly different, are well-correlated.
Oral temperatures are influenced by drinking, chewing, smoking, and breathing with the mouth open. Mouth breathing, cold drinks or food reduce oral temperatures; hot drinks, hot food, chewing, and smoking raise oral temperatures.
Each measurement method also has different normal ranges depending on sex.
Many outside factors affect the measured temperature as well. "Normal" values are generally given for an otherwise healthy, non-fasting adult, dressed comfortably, indoors, in a room that is kept at a normal room temperature, 22.7 to 24.4 °C (73 to 76 °F), during the morning, but not shortly after arising from sleep. Furthermore, for oral temperatures, the subject must not have eaten, drunk, or smoked anything in at least the previous fifteen to twenty minutes, as the temperature of the food, drink, or smoke can dramatically affect the reading.
Temperature is increased after eating or drinking anything with calories. Caloric restriction, as for a weight-loss diet, decreases overall body temperature. Drinking alcohol decreases the amount of daily change, slightly lowering daytime temperatures and noticeably raising nighttime temperatures.
Exercise raises body temperatures. In adults, a noticeable increase usually requires strenuous exercise or exercise sustained over a significant time. Children develop higher temperatures with milder activities, like playing.
Psychological factors also influence body temperature: a very excited person often has an elevated temperature.
Sleep disturbances also affect temperatures. Normally, body temperature drops significantly at a person's normal bedtime and throughout the night. Short-term sleep deprivation produces a higher temperature at night than normal, but long-term sleep deprivation appears to reduce temperatures. Insomnia and poor sleep quality are associated with smaller and later drops in body temperature. Similarly, waking up unusually early, sleeping in, jet lag and changes to shift work schedules may affect body temperature.
A temperature setpoint is the level at which the body attempts to maintain its temperature. When the setpoint is raised, the result is a fever. Most fevers are caused by infectious disease and can be lowered, if desired, with antipyretic medications.
An early morning temperature higher than 37.2 °C (99.0 °F) or a late afternoon temperature higher than 37.7 °C (99.9 °F) is normally considered a fever, assuming that the temperature is elevated due to a change in the hypothalamus's setpoint. Lower thresholds are sometimes appropriate for elderly people. The normal daily temperature variation is typically 0.5 °C (0.90 °F), but can be greater among people recovering from a fever.
Hyperthermia occurs when the body produces or absorbs more heat than it can dissipate. It is usually caused by prolonged exposure to high temperatures. The heat-regulating mechanisms of the body eventually become overwhelmed and unable to deal effectively with the heat, causing the body temperature to climb uncontrollably. Hyperthermia at or above about 40 °C (104 °F) is a life-threatening medical emergency that requires immediate treatment. Common symptoms include headache, confusion, and fatigue. If sweating has resulted in dehydration, then the affected person may have dry, red skin.
In a medical setting, mild hyperthermia is commonly called heat exhaustion or heat prostration; severe hyperthermia is called heat stroke. Heat stroke may come on suddenly, but it usually follows the untreated milder stages. Treatment involves cooling and rehydrating the body; fever-reducing drugs are useless for this condition. This may be done through moving out of direct sunlight to a cooler and shaded environment, drinking water, removing clothing that might keep heat close to the body, or sitting in front of a fan. Bathing in tepid or cool water, or even just washing the face and other exposed areas of the skin, can be helpful.
With fever, the body's core temperature rises to a higher temperature through the action of the part of the brain that controls the body temperature; with hyperthermia, the body temperature is raised without the influence of the heat control centers.
In hypothermia, body temperature drops below that required for normal metabolism and bodily functions. In humans, this is usually due to excessive exposure to cold air or water, but it can be deliberately induced as a medical treatment. Symptoms usually appear when the body's core temperature drops by 1–2 °C (1.8–3.6 °F) below normal temperature.
Basal body temperature is the lowest temperature attained by the body during rest (usually during sleep). It is generally measured immediately after awakening and before any physical activity has been undertaken, although the temperature measured at that time is somewhat higher than the true basal body temperature. In women, temperature differs at various points in the menstrual cycle, and this can be used in the long-term to track ovulation both for the purpose of aiding conception or avoiding pregnancy. This process is called fertility awareness.
Core temperature, also called core body temperature, is the operating temperature of an organism, specifically in deep structures of the body such as the liver, in comparison to temperatures of peripheral tissues. Core temperature is normally maintained within a narrow range so that essential enzymatic reactions can occur. Significant core temperature elevation (hyperthermia) or depression (hypothermia) that is prolonged for more than a brief period of time is incompatible with human life.
Temperature examination in the rectum is the traditional gold standard measurement used to estimate core temperature (oral temperature is affected by hot or cold drinks and mouth-breathing). Rectal temperature is expected to be approximately one Fahrenheit degree higher than an oral temperature taken on the same person at the same time. Ear thermometers measure eardrum temperature using infrared sensors. The blood supply to the tympanic membrane is shared with the brain. However, this method of measuring body temperature is not as accurate as rectal measurement and has a low sensitivity for fevers, missing three or four out of every ten fevers in children. Ear temperature measurement may be acceptable for observing trends in body temperature but is less useful in consistently identifying fevers.
Until recently, direct measurement of core body temperature required surgical insertion of a probe, so a variety of indirect methods have commonly been used. The rectal or vaginal temperature is generally considered to give the most accurate assessment of core body temperature, particularly in hypothermia. In the early 2000s, ingestible thermistors in capsule form were produced, allowing the temperature inside the digestive tract to be transmitted to an external receiver; one study found that these were comparable in accuracy to rectal temperature measurement.
In the 19th century, most books quoted "blood heat" as 98 °F, until a study published the mean (but not the variance) of a large sample as 36.88 °C (98.38 °F). Subsequently that mean was widely quoted as "37 °C or 98.4 °F" until editors realised 37 °C is closer to 98.6 °F than 98.4 °F. The 37 °C value was set by German physician Carl Reinhold August Wunderlich in his 1868 book , which put temperature charts into widespread clinical use . Dictionaries and other sources that quoted these averages did add the word "about" to show that there is some variance, but generally did not state how wide the variance is.
Dantrolene may also be associated with improved survival and reduced complications, especially in patients with extreme (≥ 42 °C) or severe (≥ 40 °C) hyperpyrexia
Despite the myriad of complications associated with heat illness, an elevation of core temperature above 41.0 °C (often referred to as fever or hyperpyrexia) is the most widely recognized symptom of this syndrome.
"98.6" is a song written by Tony Powers (lyrics) and George Fischoff (music) and performed by Keith. The song reached No. 7 on the Billboard chart and No. 24 on the UK Singles Chart in 1967. The song appeared on his 1967 album 98.6/Ain't Gonna Lie. The Tokens, who had provided the backing vocals on Keith's debut single, "Ain't Gonna Lie", also provided the backing vocals for "98.6".The song was produced by Jerry Ross and arranged by Joe Renzetti. It sold over one million copies worldwide, earning a gold disc. The track's title relates to the normal human body temperature in degrees Fahrenheit. The personnel on "98.6" included Artie Butler on organ and piano, Vinnie Bell on guitar, Joe Macko on bass, and Bobby Gregg on drums. The song also features a brass section of trumpets and trombones as well. The song is noted for its slow piano introduction, before the rhythm changes to 6/8 time.Aspergillus fumigatus
Aspergillus fumigatus is a species of fungus in the genus Aspergillus, and is one of the most common Aspergillus species to cause disease in individuals with an immunodeficiency.
Aspergillus fumigatus, a saprotroph widespread in nature, is typically found in soil and decaying organic matter, such as compost heaps, where it plays an essential role in carbon and nitrogen recycling. Colonies of the fungus produce from conidiophores; thousands of minute grey-green conidia (2–3 μm) which readily become airborne. For many years, A. fumigatus was thought to only reproduce asexually, as neither mating nor meiosis had ever been observed. In 2008, A. fumigatus was shown to possess a fully functional sexual reproductive cycle, 145 years after its original description by Fresenius. Although A. fumigatus occurs in areas with widely different climates and environments, it displays low genetic variation and a lack of population genetic differentiation on a global scale. Thus, the capability for sex is maintained, though little genetic variation is produced.
The fungus is capable of growth at 37 °C or 99 °F (normal human body temperature), and can grow at temperatures up to 50 °C or 122 °F, with conidia surviving at 70 °C or 158 °F—conditions it regularly encounters in self-heating compost heaps. Its spores are ubiquitous in the atmosphere, and everybody inhales an estimated several hundred spores each day; typically, these are quickly eliminated by the immune system in healthy individuals. In immunocompromised individuals, such as organ transplant recipients and people with AIDS or leukemia, the fungus is more likely to become pathogenic, over-running the host's weakened defenses and causing a range of diseases generally termed aspergillosis. Several virulence factors have been postulated to explain this opportunistic behaviour.When the fermentation broth of A. fumigatus was screened, a number of indolic alkaloids with antimitotic properties were discovered. The compounds of interest have been of a class known as tryprostatins, with spirotryprostatin B being of special interest as an anticancer drug.
Aspergillus fumigatus grown on certain building materials can produce genotoxic and cytotoxic mycotoxins, such as gliotoxin.Babassu oil
Babassu oil or cusi oil is a clear light yellow vegetable oil extracted from the seeds of the babassu palm (Attalea speciosa), which grows in the Amazon region of South America. It is a non-drying oil used in food, cleaners and skin products. This oil has properties similar to coconut oil and is used in much the same context. It is increasingly being used as a substitute for coconut oil. Babassu oil is about 70% lipids, in the following proportions:
Lauric and myristic acids have melting points relatively close to human body temperature, so babassu oil can be applied to the skin as a solid that melts on contact. This heat transfer can produce a cooling sensation. It is an effective emollient.
During February 2008, a mixture of babassu oil and coconut oil was used to partially power one engine of a Boeing 747, in a biofuel trial sponsored by Virgin Atlantic Airways.Carl Reinhold August Wunderlich
Carl Reinhold August Wunderlich (4 August 1815, Sulz am Neckar – 25 September 1877, Leipzig) was a German physician, pioneer psychiatrist, and medical professor. He is known for his measurement of mean healthy human body temperature of 37 °C (98.6 °F), now known more accurately to be about 36.8 °C (98.2 °F).He attended grammar school in Stuttgart and at the age of eighteen he began his medical studies at Tübingen University, where he completed his final exams in 1837. In 1838 he worked as assistant at St Catharine's Hospital in Stuttgart, and wrote his MD thesis. Two years later he wrote his MD habilitation on internal medicine at Tübingen University
In 1846 he was appointed Professor (ordentlicher Professor) and head of the general hospital at Tübingen. Four years later he moved to Leipzig University as Professor and Medical Director of the university hospital. There he introduced clinical pedagogy, combined with a rigorous methodology of diagnosis, and empirical observation of patients. He introduced temperature charts into hospitals, holding that fever is not a disease, but a symptom. The thermometer he used was reportedly a foot long, and required 20 minutes to register the temperature.
He was known for his lectures on psychiatry and on the "pathology and therapy of illnesses of the nervous system." He described an extremely rare eponymous syndrome which consists of retroperitoneal bleeding from the kidney which tracks into the surrounding tissues. This may be due to benign or malignant disease. In 1871 he was appointed to the Department of Medicine's organisational commission for the construction and design of psychiatric hospitals.Cocoa butter
Cocoa butter, also called theobroma oil, is a pale-yellow, edible vegetable fat extracted from the cocoa bean. It is used to make chocolate, as well as some ointments, toiletries, and pharmaceuticals. Cocoa butter has a cocoa flavor and aroma. Its melting point is just below human body temperature.Conversion of units of temperature
This is a collection of temperature conversion formulas and comparisons among eight different temperature scales, several of which have long been obsolete.Degree (temperature)
The term degree is used in several scales of temperature. The symbol ° is usually used, followed by the initial letter of the unit, for example “°C” for degree(s) Celsius. A degree can be defined as a set change in temperature measured against a given scale, for example, one degree Celsius is one hundredth of the temperature change between the point at which water starts to change state from solid to liquid state and the point at which it starts to change from its gaseous state to liquid.Dimorphic fungus
Dimorphic fungi are fungi that can exist in the form of both mold and yeast. An example is Penicillium marneffei, a human pathogen that grows as a mold at room temperature, and as a yeast at human body temperature.Fahrenheit
The Fahrenheit scale is a temperature scale based on one proposed in 1724 by Dutch–German–Polish physicist Daniel Gabriel Fahrenheit (1686–1736). It uses the degree Fahrenheit (symbol: °F) as the unit. Several accounts of how he originally defined his scale exist. The lower defining point, 0 °F, was established as the freezing temperature of a solution of brine made from equal parts of ice, water and salt (ammonium chloride). Further limits were established as the melting point of ice (32 °F) and his best estimate of the average human body temperature (96 °F, about 2.6 °F less than the modern value due to a later redefinition of the scale). The scale is now usually defined by two fixed points: the temperature at which water freezes into ice is defined as 32 °F, and the boiling point of water is defined to be 212 °F, a 180 °F separation, as defined at sea level and standard atmospheric pressure.
At the end of the 2010s, Fahrenheit was used as the official temperature scale only in the United States (including its unincorporated territories), its freely associated states in the Western Pacific (Palau, the Federated States of Micronesia and the Marshall Islands), the Bahamas, the Cayman Islands and Liberia. Antigua and Barbuda and other islands which use the same meteorological service, such as Anguilla, the British Virgin Islands, Montserrat and Saint Kitts and Nevis, as well as Bermuda, Belize and the Turks and Caicos Islands, use Fahrenheit and Celsius. All other countries in the world officially now use the Celsius scale, named after Swedish astronomer Anders Celsius.False precision
False precision (also called overprecision, fake precision, misplaced precision and spurious precision) occurs when numerical data are presented in a manner that implies better precision than is justified; since precision is a limit to accuracy, this often leads to overconfidence in the accuracy, named precision bias.FourU thermometer
FourU thermometers are a class of non-coding RNA thermometers found in Salmonella. They are named 'FourU' due to the four highly conserved uridine nucleotides found directly opposite the Shine-Dalgarno sequence on hairpin II (pictured).
RNA thermometers such as FourU control regulation of temperature via heat shock proteins in many prokaryotes. FourU thermometers are relatively small RNA molecules, only 57 nucleotides in length, and have a simple two-hairpin structure.FourU are found in the 5' untranslated region of the gene for heat shock protein Salmonella agsA, they repress translation of this protein by base-pairing the Shine-Dalgardo sequence of the gene's mRNA. This prevents ribosomes from binding the gene's start codon.They are also found in the 5'UTR of htrA (high temperature requirement) genes in Salmonella and E.coli.In V. cholerae fourU thermometer in the 5' of toxT controls its temperature-dependant translation. At human body temperature, the thermometer structure opens and to allow transcriptional activator protein ToxT translation, facilitating V. cholerae virulance.Other known RNA thermometers include the ROSE element and Hsp90 cis-reg element.Gallium
Gallium is a chemical element with symbol Ga and atomic number 31. It is in group 13 of the periodic table, and thus has similarities to the other metals of the group, aluminium, indium, and thallium. Gallium does not occur as a free element in nature, but as gallium(III) compounds in trace amounts in zinc ores and in bauxite. Elemental gallium is a soft, silvery blue metal at standard temperature and pressure, a brittle solid at low temperatures, and a liquid at temperatures greater than 29.76 °C (85.57 °F) (above room temperature, but below the normal human body temperature of 98.6 °F (37.0 °C), hence, the metal will melt in a person's hands).
The melting point of gallium is used as a temperature reference point. Gallium alloys are used in thermometers as a non-toxic and environmentally friendly alternative to mercury, and can withstand higher temperatures than mercury. The alloy galinstan (70% gallium, 21.5% indium, and 10% tin) has an even lower melting point of −19 °C (−2 °F), well below the freezing point of water.
Since its discovery in 1875, gallium has been used to make alloys with low melting points. It is also used in semiconductors as a dopant in semiconductor substrates.
Gallium is predominantly used in electronics. Gallium arsenide, the primary chemical compound of gallium in electronics, is used in microwave circuits, high-speed switching circuits, and infrared circuits. Semiconducting gallium nitride and indium gallium nitride produce blue and violet light-emitting diodes (LEDs) and diode lasers. Gallium is also used in the production of artificial gadolinium gallium garnet for jewelry.
Gallium has no known natural role in biology. Gallium(III) behaves in a similar manner to ferric salts in biological systems and has been used in some medical applications, including pharmaceuticals and radiopharmaceuticals.Heated humidified high-flow therapy
Heated humidified high-flow (HHHF) therapy is a type of respiratory support method that delivers a high flow (liters per minute) of medical gas to a patient through an interface (nasal cannulae) intended to create a wash-out of the upper airway. The applied gas is heated to best match human body temperature (37 Celsius) and humidified targeting ideal body saturation vapor pressure.Hot spring
A hot spring is a spring produced by the emergence of geothermally heated groundwater that rises from the Earth's crust. While some of these springs contain water that is a safe temperature for bathing, others are so hot that immersion can result in injury or death.PrfA thermoregulator UTR
The PrfA thermoregulator UTR is an RNA thermometer found in the 5' UTR of the prfA gene. In Listeria monocytogenes, virulence genes are maximally expressed at 37 °C (human body temperature) but are almost silent at 30 °C. The genes are controlled by PrfA, a transcriptional activator whose expression is thermoregulated. It has been shown that the untranslated mRNA (UTR) preceding prfA, forms a secondary structure, which masks the ribosome binding region. It is thought that at 37 °C, the hairpin structure 'melts' and the SD sequence is unmasked.Spiroplasma
Spiroplasma is a genus of Mollicutes, a group of small bacteria without cell walls. Spiroplasma shares the simple metabolism, parasitic lifestyle, fried-egg colony morphology and small genome of other Mollicutes, but has a distinctive helical morphology, unlike Mycoplasma. It has a spiral shape and moves in a corkscrew motion. Many Spiroplasma are found either in the gut or haemolymph of insects where they can act to manipulate host reproduction, or defend the host as endosymbionts. Spiroplasma are also disease-causing agents in the phloem of plants. Spiroplasmas are fastidious organisms, which require a rich culture medium. Typically they grow well at 30 °C, but not at 37 °C. A few species, notably Spiroplasma mirum, grow well at 37 °C (human body temperature), and cause cataracts and neurological damage in suckling mice. The best studied species of spiroplasmas are Spiroplasma poulsonii, a reproductive manipulator and defensive insect symbiont, Spiroplasma citri, the causative agent of citrus stubborn disease, and Spiroplasma kunkelii, the causative agent of corn stunt disease.Temperature (disambiguation)
Temperature is a physical property of a system that underlies the common notions of hot and cold.
Closely related are:
Normal human body temperatureThe term may also refer to:
Noise temperature, a measure of the noise of an electronic component.
Temperature (game theory), a measure of the value of a game to its players.
Temperature (meat), or doneness, a description of how thoroughly cooked a cut of meat is
Fever, pyrexia, or having a temperature, the elevation of the body temperature.Temperature measurement
Temperature measurement, also known as thermometry, describes the process of measuring a current local temperature for immediate or later evaluation. Datasets consisting of repeated standardized measurements can be used to assess temperature trends.Yersinia enterocolitica
Yersinia enterocolitica is a Gram-negative bacillus-shaped bacterium, belonging to the family Enterobacteriaceae. It is motile at temperatures of 22–29°C, but becomes nonmotile at normal human body temperature. Y. enterocolitica infection causes the disease yersiniosis, which is an animal-borne disease occurring in humans, as well as in a wide array of animals such as cattle, deer, pigs, and birds. Many of these animals recover from the disease and become carriers; these are potential sources of contagion despite showing no signs of disease. The bacterium infects the host by sticking to its cells using trimeric autotransporter adhesins.
The genus Yersinia includes 11 species:
Y. pestis, Y. pseudotuberculosis, Y. enterocolitica, Y. frederiksenii,
Y. intermedia, Y. kristensenii, Y. bercovieri, Y. mollaretii, Y. rohdei, Y. aldovae, and Y. ruckeri. Among them, only Y. pestis, Y. pseudotuberculosis, and certain strains of Y. enterocolitica are of pathogenic importance for humans and certain warm-blooded animals, whereas the other species are of environmental origin and may, at best, act as opportunists. However, Yersinia strains can be isolated from clinical materials, so they have to be identified at the species level.
Y. enterocolitica is a heterogeneous group of strains, which are traditionally classified by biotyping into six biogroups on the basis of phenotypic characteristics, and by serotyping into more than 57 O serogroups, on the basis of their O (lipopolysaccharide or LPS) surface antigen. Five of the six biogroups (1B and 2–5) are regarded as pathogens. However, only a few of these serogroups have been associated with disease in either humans or animals. Strains that belong to serogroups O:3 (biogroup 4), O:5,27 (biogroups 2 and 3), O:8 (biogroup 1B), and O:9 (biogroup 2) are most frequently isolated worldwide from human samples. However, the most important Y. enterocolitica serogroup in many European countries is serogroup O:3 followed by O:9, whereas the serogroup O:8 is mainly detected in the United States.
Y. enterocolitica is widespread in nature, occurring in reservoirs ranging from the intestinal tracts of numerous mammals, avian species, cold-blooded species, and even from terrestrial and aquatic niches. Most environmental isolates are avirulent; however, isolates recovered from porcine sources contain human pathogenic serogroups. In addition, dogs, sheep, wild rodents, and environmental water may also be a reservoir of pathogenic Y. enterocolitica strains. Human pathogenic
strains are usually confined to the intestinal tract and lead to enteritis/diarrhea.