The typical signs and symptoms of cellulitis is an area which is red, hot, and painful. The photos shown here of are of mild to moderate cases, and are not representative of earlier stages of the condition.

Cellulitis is caused by a type of bacteria entering the skin, usually by way of a cut, abrasion, or break in the skin. This break does not need to be visible. Group A "Streptococcus" and "Staphylococcus" are the most common of these bacteria, which are part of the normal flora of the skin, but normally cause no actual infection while on the skin's outer surface.

About 80% of cases of Ludwig's angina, or cellulitis of the submandibular space, are caused by dental infections. Mixed infections, due to both aerobes and anaerobes, are commonly associated with this type of cellulitis. Typically, this includes alpha-hemolytic streptococci, staphylococci, and bacteroides groups.

Predisposing conditions for cellulitis include insect or spider bite, blistering, animal bite, tattoos, pruritic (itchy) skin rash, recent surgery, athlete's foot, dry skin, eczema, injecting drugs (especially subcutaneous or intramuscular injection or where an attempted intravenous injection "misses" or blows the vein), pregnancy, diabetes, and obesity, which can affect circulation, as well as burns and boils, though debate exists as to whether minor foot lesions contribute. Occurrences of cellulitis may also be associated with the rare condition hidradenitis suppurativa or dissecting cellulitis.

The appearance of the skin assists a doctor in determining a diagnosis. A doctor may also suggest blood tests, a wound culture, or other tests to help rule out a blood clot deep in the veins of the legs. Cellulitis in the lower leg is characterized by signs and symptoms similar to those of a deep vein thrombosis, such as warmth, pain, and swelling (inflammation).

This reddened skin or rash may signal a deeper, more serious infection of the inner layers of skin. Once below the skin, the bacteria can spread rapidly, entering the lymph nodes and the bloodstream and spreading throughout the body. This can result in influenza-like symptoms with a high temperature and sweating or feeling very cold with shaking, as the sufferer cannot get warm.

In rare cases, the infection can spread to the deep layer of tissue called the fascial lining. Necrotizing fasciitis, also called by the media "flesh-eating bacteria", is an example of a deep-layer infection. It is a medical emergency.

Orbital cellulitis

is inflammation of eye tissues behind the orbital septum. It most commonly refers to an acute spread of infection into the eye socket from either the adjacent sinuses or through the blood. It may also occur after trauma.

When it affects the rear of the eye, it is known as retro-orbital cellulitis.

It should not be confused with periorbital cellulitis, which refers to cellulitis anterior to the septum.

Common signs and symptoms of orbital cellulitis include pain with eye movement, sudden vision loss, chemosis, bulging of the infected eye, and limited eye movement. Along with these symptoms, patients typically have redness and swelling of the eyelid, pain, discharge, inability to open the eye, occasional fever and lethargy. It is usually caused by a previous sinusitis. Other causes include infection of nearby structures, trauma and previous surgery.

People usually complain of intense pain that may seem excessive given the external appearance of the skin. People initially have signs of inflammation, fever and a fast heart rate. With progression of the disease, often within hours, tissue becomes progressively swollen, the skin becomes discolored and develops blisters. Crepitus may be present and there may be a discharge of fluid, said to resemble "dish-water". Diarrhea and vomiting are also common symptoms.

In the early stages, signs of inflammation may not be apparent if the bacteria are deep within the tissue. If they are "not" deep, signs of inflammation, such as redness and swollen or hot skin, develop very quickly. Skin color may progress to violet, and blisters may form, with subsequent necrosis (death) of the subcutaneous tissues.

Furthermore, people with necrotizing fasciitis typically have a fever and appear sick. Mortality rates are as high as 73% if left untreated. Without surgery and medical assistance, such as antibiotics, the infection will rapidly progress and will eventually lead to death.

When it affects the groin it is known as Fournier gangrene.

Periorbital cellulitis must be differentiated from orbital cellulitis, which is an emergency and requires intravenous (IV) antibiotics. In contrast to orbital cellulitis, patients with periorbital cellulitis do not have bulging of the eye (proptosis), limited eye movement (ophthalmoplegia), pain on eye movement, or loss of vision. If any of these features is present, one must assume that the patient has orbital cellulitis and begin treatment with IV antibiotics. CT scan may be done to delineate the extension of the infection.

Affected individuals may experience the following;

swelling,

redness,

discharge,

pain,

shut eye,

conjunctival injection,

fever (mild), slightly blurred vision, teary eyes, and some reduction in vision.

Typical signs include periorbital erythema, induration, tenderness and warmth.

Abscesses may occur in any kind of solid tissue but most frequently on skin surface (where they may be superficial pustules (boils) or deep skin abscesses), in the lungs, brain, teeth, kidneys, and tonsils. Major complications are spreading of the abscess material to adjacent or remote tissues, and extensive regional tissue death (gangrene).

The main symptoms and signs of a skin abscess are redness, heat, swelling, pain, and loss of function. There may also be high temperature (fever) and chills.

An internal abscess is more difficult to identify, but signs include pain in the affected area, a high temperature, and generally feeling unwell.

Internal abscesses rarely heal themselves, so prompt medical attention is indicated if such an abscess is suspected.

An abscess could potentially be fatal (although this is rare) if it compresses vital structures such as the trachea in the context of a deep neck abscess.

If superficial, abscesses may be fluctuant when palpated. This is a wave-like motion that is caused by movement of the pus inside the abscess.

This most common form of impetigo, also called nonbullous impetigo, most often begins as a red sore near the nose or mouth which soon breaks, leaking pus or fluid, and forms a honey-colored scab, followed by a red mark which heals without leaving a scar. Sores are not painful, but they may be itchy. Lymph nodes in the affected area may be swollen, but fever is rare. Touching or scratching the sores may easily spread the infection to other parts of the body.

Skin ulcers with redness and scarring also may result from scratching or abrading the skin.

Tuberculous cellulitis is a skin condition resulting from infection with mycobacterium, and presenting as cellulitis.

Ecthyma, the nonbullous form of impetigo, produces painful fluid- or pus-filled sores with redness of skin, usually on the arms and legs, become ulcers that penetrate deeper into the dermis. After they break open, they form hard, thick, gray-yellow scabs, which sometimes leave scars. Ecthyma may be accompanied by swollen lymph nodes in the affected area.

Affected individuals typically develop symptoms including high fevers, shaking, chills, fatigue, headaches, vomiting, and general illness within 48 hours of the initial infection. The erythematous skin lesion enlarges rapidly and has a sharply demarcated, raised edge. It appears as a red, swollen, warm, and painful rash, similar in consistency to an orange peel. More severe infections can result in vesicles (pox or insect bite-like marks), blisters, and petechiae (small purple or red spots), with possible skin necrosis (death). Lymph nodes may be swollen, and lymphedema may occur. Occasionally, a red streak extending to the lymph node can be seen.

The infection may occur on any part of the skin, including the face, arms, fingers, legs, and toes; it tends to favour the extremities. Fat tissue and facial areas, typically around the eyes, ears, and cheeks, are most susceptible to infection. Repeated infection of the extremities can lead to chronic swelling (lymphangitis).

Anaerobes can be isolated from most types of upper respiratory tract and head and neck and infection and are especially common in chronic ones. These include tonsillar, peritonsillar and retropharyngeal abscesses, chronic otitis media, sinusitis and mastoiditis, eye ocular) infections, all deep neck space infections, parotitis, sialadenitis, thyroiditis, odontogenic infections, and postsurgical and nonsurgical head and neck wounds and abscesses., The predominant organisms are of oropharyngeal flora origin and include AGNB, "Fusobacterium" and Peptostreptococcus spp.

Anaerobes involve almost all dental infections. These include dental abscesses, endodontal pulpitis and periodontal (gingivitis and periodontitis) infections, and perimandibular space infection. Pulpitis can lead to abscess formation and eventually spread to the mandible and other neck spaces. In addition to strict anaerobic bacteria, microaerophilic streptococci and "Streptococcus salivarius" can also be present.

"Fusobacterium" spp. and anaerobic spirochetes are often the cause of acute necrotizing ulcerative gingivitis (or Vincent's angina) which is a distinct form of ulcerative gingivitis.

Deep neck infections that develop as a consequence of oral, dental and pharyngeal infections are generally polymicrobial in nature. These include extension of retropharyngeal cellulitis or abscess, mediastinitis following esophagus perforation, and dental or periodontal abscess.

Boils are bumpy, red, pus-filled lumps around a hair follicle that are tender, warm, and very painful. They range from pea-sized to golf ball-sized. A yellow or white point at the center of the lump can be seen when the boil is ready to drain or discharge pus. In a severe infection, an individual may experience fever, swollen lymph nodes, and fatigue. A recurring boil is called chronic furunculosis. Skin infections tend to be recurrent in many patients and often spread to other family members. Systemic factors that lower resistance commonly are detectable, including: diabetes, obesity, and hematologic disorders. Boils can be caused by other skin conditions that cause the person to scratch and damage the skin.

Boils may appear on the buttocks or near the anus, the back, the neck, the stomach, the chest, the arms or legs, or even in the ear canal. Boils may also appear around the eye, where they are called styes. A boil on the gum is called intraoral dental sinus, or more commonly, a gumboil.

"Staphylococcus aureus", "Streptococcus pneumoniae", other streptococci, and anaerobes are the most common causes, depending on the origin of the infection.

The advent of the "Haemophilus influenzae" vaccine has dramatically decreased the incidence.

Necrotizing fasciitis (NF), commonly known as flesh-eating disease, is an infection that results in the death of the body's soft tissue. It is a severe disease of sudden onset that spreads rapidly. Symptoms include red or purple skin in the affected area, severe pain, fever, and vomiting. The most commonly affected areas are the limbs and perineum.

Typically the infection enters the body through a break in the skin such as a cut or burn. Risk factors include poor immune function such as from diabetes or cancer, obesity, alcoholism, intravenous drug use, and peripheral vascular disease. It is not typically spread between people. The disease is classified into four types, depending on the infecting organism. Between 55% and 80% of cases involve more than one type of bacteria. Methicillin-resistant "Staphylococcus aureus" (MRSA) is involved in up to a third of cases. Medical imaging is helpful to confirm the diagnosis.

Prevention is by good wound care and handwashing. It is usually treated with surgery to remove the infected tissue and intravenous antibiotics. Often a combination of antibiotics are used such as penicillin G, clindamycin, vancomycin, and gentamicin. Delays in surgery are associated with a higher risk of death. Despite high quality treatment the risk of death is between 25% and 35%.

Necrotizing fasciitis affects 0.4 to 1 person per 100,000 per year. Both sexes are affected equally. It becomes more common among older people and is very rare in children. Necrotizing fasciitis has been described at least since the time of Hippocrates. The term "necrotising fasciitis" first came into use in 1952.

Surgery of the anal fistula to drain an abscess treats the fistula and reduces likelihood of its recurrence and the need for repeated surgery. There is no evidence that fecal incontinence is a consequence of this surgery for abscess drainage.

Perianal abscesses can be seen in patients with for example inflammatory bowel disease (such as Crohn's disease) or diabetes. Often the abscess will start as an internal wound caused by ulceration, hard stool or penetrative objects with insufficient lubrication. This wound typically becomes infected as a result of the normal presence of feces in the rectal area, and then develops into an abscess. This often presents itself as a lump of tissue near the anus which grows larger and more painful with time. Like other abscesses, perianal abscesses may require prompt medical treatment, such as an incision and debridement or lancing.

Aeromonas infections may cause skin infections manifesting as cellulitis, pustules, and furuncles. An infection usually only causes mild infections of the skin but can also cause a more a serious infection called gastroenteritis?

Secondary peritonitis and intra-abdominal abscesses including splenic and hepatic abscesses generally occur because of the entry of enteric micro-organisms into the peritoneal cavity through a defect in the wall of the intestine or other viscus as a result of obstruction, infarction or direct trauma. Perforated appendicitis, diverticulitis, inflammatory bowel disease with perforation and gastrointestinal surgery are often associated with polymicrobial infections caused by aerobic and anaerobic bacteria, where the number of isolates can average 12 (two-thirds are generally anaerobes). The most common aerobic and facultative bacteria are "Escherichia coli", "Streptococcus" spp. (including Enterococcus spp.), and the most frequently isolated anaerobic bacteria are the "B. fragilis" group, "Peptostreptococcus" spp., and "Clostridium" spp.

Abdominal infections are characteristically biphasic: an initial stages of generalized peritonitis associated with "Escherichia coli" sepsis, and a later stages, in which intra abdominal abscesses harboring anaerobic bacteria ( including "B. fragilis" group ) emerge.

The clinical manifestations of secondary peritonitis are a reflection of the underlying disease process. Fever, diffuse abdominal pain, nausea and vomiting are common. Physical examination generally show signs of peritoneal inflammation, isuch as rebound tenderness, abdominal wall rigidity and decrease in bowel sounds. These early findings may be followed by signs and symptoms of shock.

Biliary tract infection is usually caused by "E. coli, Klebsiella" and "Enterococcus" spp. Anaerobes (mostly "B. fragilis" group, and rarely "C. perfringens") can be recovered in complicated infections associated with carcinoma, recurrent infection, obstruction, bile tract surgery or manipulation.

Laboratory studies show elevated blood leukocyte count and predominance of polymorphonuclear forms. Radiographs studies may show free air in the peritoneal cavity, evidence of ileus or obstruction and obliteration of the psoas shadow. Diagnostic ultrasound, gallium and CT scanning may detect appendiceal or other intra-abdominal abscesses. Polymicrobial postoperative wound infections can occur.

Treatment of mixed aerobic and anaerobic abdominal infections requires the utilization of antimicrobials effective against both components of the infection as well as surgical correction and drainage of pus. Single and easily accessible abscesses can be drained percutaneously.

The first symptom is a sudden onset of swelling of the face, which develops within two days into papules and pustues on the lips, nose, and around the eyes. These pustules release a purulent discharge, causing a crust to form on the skin. There is also lymphadenopathy (swelling of lymph nodes) in the main lymph nodes of the head. The feet, body, prepuce or perianal area may be affected. Pustular otitis externa can occur, with the pinnae (ear flaps) becoming thickened by edema. Affected areas are painful but not itchy. Approximately half of affected puppies have lethargy and depression. Less common symptoms include pyrexia, anorexia, and joint pain, caused by sterile suppurative arthritis.

Erysipelas is an acute infection typically with a skin rash, usually on any of the legs and toes, face, arms, and fingers. It is an infection of the upper dermis and superficial lymphatics, usually caused by beta-hemolytic group A "Streptococcus" bacteria on scratches or otherwise infected areas. Erysipelas is more superficial than cellulitis, and is typically more raised and demarcated. The term is from Greek ἐρυσίπελας, meaning "red skin".

Clinically, neonates with omphalitis present within the first two weeks of life with signs and symptoms of a skin infection (cellulitis) around the umbilical stump (redness, warmth, swelling, pain), pus from the umbilical stump, fever, fast heart rate (tachycardia), low blood pressure (hypotension), somnolence, poor feeding, and yellow skin (jaundice). Omphalitis can quickly progress to sepsis and presents a potentially life-threatening infection. In fact, even in cases of omphalitis without evidence of more serious infection such as necrotizing fasciitis, mortality is high (in the 10% range).

A boil, also called a furuncle, is a deep folliculitis, infection of the hair follicle. It is most commonly caused by infection by the bacterium "Staphylococcus aureus", resulting in a painful swollen area on the skin caused by an accumulation of pus and dead tissue. Boils which are expanded are basically pus-filled nodules. Individual boils clustered together are called carbuncles.

Most human infections are caused by coagulase-positive "S. aureus" strains, notable for the bacteria's ability to produce coagulase, an enzyme that can clot blood. Almost any organ system can be infected by "S. aureus".

Ludwig's angina is a fascial space infection with bilateral involvement of the submandibular, sublingual and submental spaces. The external signs may include bilateral lower facial edema around the mandible and upper neck. Intraoral signs may include a raised floor of mouth due to sublingual space involvement and posterior displacement of the tongue. Symptoms may include dysphagia, pain with swallowing, difficulty breathing, and pain.

Ludwig's angina should be treated urgently due to the airway being compromised. The infection may rapidly spread to other fascial spaces of the head and neck, further compromising the airway.

A skin and skin structure infection (SSSI), also referred to as skin and soft tissue infection (SSTI) or acute bacterial skin and skin structure infection (ABSSSI), is an infection of skin and associated soft tissues (such as loose connective tissue and mucous membranes). The pathogen involved is usually a bacterial species. Such infections often requires treatment by antibiotics.

Until 2008, two types were recognized, complicated skin and skin structure infection (cSSSI) and uncomplicated skin and skin structure infection (uSSSI). "Uncomplicated" SSSIs included simple abscesses, impetiginous lesions, furuncles, and cellulitis. "Complicated" SSSIs included infections either involving deeper soft tissue or requiring significant surgical intervention, such as infected ulcers, burns, and major abscesses or a significant underlying disease state that complicates the response to treatment. Superficial infections or abscesses in an anatomical site, such as the rectal area, where the risk of anaerobic or gram-negative pathogen involvement is higher, should be considered complicated infections. The two categories had different regulatory approval requirements. The uncomplicated category (uSSSI) is normally only caused by "Staphylococcus aureus" and "Streptococcus pyogenes", whereas the complicated category (cSSSI) might also be caused by a number of other pathogens. In cSSSI, the pathogen is known in only about 40% of cases.

Because cSSSIs are usually serious infections, physicians do not have the time for a culture to identify the pathogen, so most cases are treated empirically, by choosing an antibiotic agent based on symptoms and seeing if it works. For less severe infections, microbiologic evaluation via tissue culture has been demonstrated to have high utility in guiding management decisions. To achieve efficacy, physicians use broad-spectrum antibiotics. This practice contributes in part to the growing incidence of antibiotic resistance, a trend exacerbated by the widespread use of antibiotics in medicine in general. The increased prevalence of antibiotic resistance is most evident in methicillin-resistant "Staphylococcus aureus" (MRSA). This species is commonly involved in cSSSIs, worsening their prognosis, and limiting the treatments available to physicians. Drug development in infectious disease seeks to produce new agents that can treat MRSA.

Since 2008, the U.S. Food and Drug Administration has changed the terminology to "acute bacterial skin and skin structure infections" (ABSSSI). The Infectious Diseases Society of America (IDSA) has retained the term "skin and soft tissue infection".

Acute rheumatic fever (ARF) is a complication of respiratory infections caused by GAS. The M-protein generates antibodies that cross-react with autoantigens on interstitial connective tissue, in particular of the endocardium and synovium, that can lead to significant clinical illness.

Although common in developing countries, ARF is rare in the United States, possibly secondary to improved antibiotic treatment, with small isolated outbreaks reported only occasionally. It is most common among children between 5 and 15 years old and occurs 1–3 weeks after an untreated GAS pharyngitis.

ARF is often clinically diagnosed based on Jones Criteria, which include: pancarditis, migratory polyarthritis of large joints, subcutaneous nodules, erythema marginatum, and sydenham chorea (involuntary, purposeless movement). The most common clinical finding is a migratory arthritis involving multiple joints.

Other indicators of GAS infection such as a DNAase or ASO serology test must confirm the GAS infection. Other minor Jones Criteria are fever, elevated ESR and arthralgia. One of the most serious complications is pancarditis, or inflammation of all three heart tissues. A fibrinous pericarditis can develop with a classic friction rub that can be auscultated. This will give increasing pain upon reclining.

Further endocarditis can develop with aseptic vegetations along the valve closure lines, in particular the mitral valve. Chronic rheumatic heart disease mostly affects the mitral valve, which can become thickened with calcification of the leaflets, often causing fusion of the commissures and chordae tendineae.

Other findings of ARF include erythema marginatum (usually over the spine or other bony areas) and a red expanding rash on the trunk and extremities that recurs over weeks to months. Because of the different ways ARF presents itself, the disease may be difficult to diagnose.

A neurological disorder, Sydenham chorea, can occur months after an initial attack, causing jerky involuntary movements, muscle weakness, slurred speech, and personality changes. Initial episodes of ARF as well as recurrences can be prevented by treatment with appropriate antibiotics.

It is important to distinguish ARF from rheumatic heart disease. ARF is an acute inflammatory reaction with pathognomonic Aschoff bodies histologically and RHD is a non-inflammatory sequela of ARF.