Musculoskeletal

There is swelling in the affected areas with restricted movement.

Dermatological

There is erythema, formation of pustules or simply swelling of the whole area involved, and later on once it starts healing, formation of scars [10].

Immune System

Due to active inflammation, there is a high neutrophil count and eosinophilia [2]. Platelet count may be increased in case of bleeding. If the inflammation goes on for more than a few hours, levels of lymphocytes in plasma may also go up.

The work up of cellulitis includes examination of the site of infection and blood cultures. The blood culture and sensitivity is done to check the causative agent so that specific antibiotics can be given.

If there is abscess formation, fine needle aspiration should be done and the pus drained out. Ultrasonography may be used for better guidance of treatment.

Laboratory

Blood tests showing the total blood count to confirm active inflammation as well as culture and sensitivity are performed to check presence of organisms.

Treatment of cellulitis is a course of antibiotics. Broad spectrum antibiotics may be administered or if deemed suitable, cultures can be sent to check for the causative organism and then specific antibiotics given [6].

Rarely there is abscess formation, but if there is, the pus should be drained and the wound should be cleaned [4].

Needle aspiration and biopsy are rarely conducted but can be carried out in special cases.

Patients with severe cellulitis are given antibiotics either intravenously or parenterally [5].

Prognosis is very good with the infection soon clearing out in a few days to weeks, depending upon its severity.

Initial Stage

Initially there is erythema and swelling in the infected area. The area becomes painful to touch, and if the involved region is in the periphery, movement may become restricted till infection resolves.

Advanced Stage

Usually, infections are resolved within a few hours to days, but if the cellulitis is left untreated or the host has a compromised immune system, the cellulitis may start showing more systemic manifestations. These may include fever with or without chills, malaise, lymphangitic spread showing red lines, pain of severe intensity and in some extremely rare cases, shock due to septicaemia.

Cellulitis always occurs due to an infection which is caused by entry of microorganism through the skin into the blood or subcutaneous tissue. As a consequence of this, inflammatory process begins. The type of infection depends upon the source, organism involved, host factors etc. Here are a few categories that may cause cellulitis:

Host Defences

Whether a person gets an infection or not, and whether it progresses to cellulitis or simply resolves on its own, depends on host factors. More specifically, it depends on host defences.
A weak immune system predisposes to severe cellulitis. Diseases like AIDS and cancer make an individual more susceptible to cellulitis whereas diseases like diabetes mellitus, arterio-venous stasis, chronic liver disease (particularly susceptible to V.vulnificus [9]) and renal diseases appear to predispose to recurrent infections.

Some families are inherently susceptible to some infections so cellulitis may be more prevalent among them.

Hospital Acquired Cellulitis

Post-operative infections leading to cellulitis around surgical incisions, although not that common, may occur in hospitalised patients.

Patients admitted due to open wounds as a result of trauma may contract infections that could result in cellulitis. The most commonly involved microorganisms in such cases include group A beta hemolytic streptococcus and Clostridium perfringens.
Patents who have undergone lymphadenectomy as a part of their cancer treatment may become a target of infections.

Secondary Cellulitis

This form of cellulitis occurs due to infection in a patient already suffering from a temporary ailment. An example of such a scenario is:
A patient of varicella or measles experiences extreme discomfort and itching around the pustules. Repeated scratching over the involved areas may cause an infection which may lead to cellulitis.

Bite Wounds

Bite wounds from animals like dogs, cats and rats may cause cellulitis due to transfer of pathogens from their saliva. The most commonly encountered bite wounds are dog bites which commonly involve organisms like Capnocytophaga canimorsus and Pastuerella multocida. Bite wounds from rats usually cause infections from Streptobacillus moniliformis.

Bites from human to other humans may sometimes result in infection, most commonly from organisms like Eikenella corrodens [3].

Puncture wounds
These may be caused by IV drug abusers where the causative agent most commonly is Staph. aureus.

Puncture wounds may occur in some athletes from their shoes from organisms like Pseudomonas. Scratches and injuries received in damp or wet areas like beaches or swamps may get infections from non-land based bacteria like Aeromonas hydrophilia, etc

Others
Tinea pedis may be associated with cellulitis between or under toes. Prolonged stay in bed may cause venous stasis leading to infection.

Cellulitis is a very common, non-reportable disease so the exact prevalence is heretofore unknown.

Sex

It has no sex predilection, occurring equally in both males and females.

Age

Generally, cellulitis has no age predilection. However, it may be noted that some particular scenarios of cellulitis are more prevalent in individuals belonging to specific age groups. A few examples of such scenarios include:

• Perianal cellulitis, often occurring due to group A beta haemolytic streptococcus is usually found in children under 3 years of age [8].
• Pneumococcal facial cellulitis is more prevalent in young children.
• Facial cellulitis by other causes is generally found more in adults over 50 years.
• Some studies reveal that cellulitis is generally found more in adults aged 45 years and above.

Race

Cellulitis has no known predilection of race. However, some microbes are found more in some particular areas so cellulitis by those organisms may be more localised there. Overall, cellulitis has no association with any ethnicity or race.

Cellulitis is an inflammation of the skin, it's layers, and the underlying subcutaneous tissue. It begins when the skin is breached by microorganisms either due to preexisting injury or a new cut, laceration or puncture. Sometimes, the skin breach may not be apparent or easily visible as it may be extremely small and may go unnoticed at first.

Once the organism has entered the body, it grows and multiplies, releasing toxins that results in active infection. When the immune system senses that there is an ongoing infection, it sends cells of the acute inflammatory cascade to battle the invading microbes.
The cells of acute inflammation include mostly neutrophils and few eosinophils.

This results in release of cytotoxic substances that paralyse or kill the invaders and lead to their phagocytosis. The temperature of the area involved increases giving calor. Vasodilation leads to redness and erythema. Swelling occurs and cellular debris accumulates, both from the cells involved as well as cells of the surrounding structures. This debris is slowly cleared away, resulting in the swelling going down after a few hours to a few days.

At times, pus may form and collect as a small pustule or a cyst but this is not very common. Sometimes, cellulitis may spread via lymphatic route to other regions creating another bout of infection there.

A safe and careful lifestyle helps in preventing infection. Wounds and injuries should be immediately treated with antiseptics and appropriately bandaged to prevent cellulitis [7].

Cellulitis, as the name indicates, is an inflammation of the skin and subcutaneous tissue. It results from an acute infection due to any microbe leading to an inflammatory process launched by the immune system to fight off the invading microorganisms [1]. This results in the following cardinal signs:

Dolor: Pain in the infected tissues and the surrounding area.

Calor: Warmth in the area involved.

Rubor: Redness or erythema of the skin around the infected area.

Tumor: Swelling of the area involved. Swelling may be minimal in mild infections or extensive in severe cases.

Functio Laesa: Normal functioning of the involved area is disturbed as the inflammatory process does its job.

Definition

Cellulitis is an infection of the skin and underlying tissues which is caused by various bacteria.

Symptoms

Symptoms include redness, swelling and warmth in the affected area. The swelling is accompanied with pain in the region. The swelling remains till the infection has resolved, which takes a few days to complete. If the wound was visible, a small scar may also form which later on disappears as well.

Complications

Complications are very rare and include fever, malaise, widespread infection and shock.

Treatment

Treatment is fairly straightforward, involving antibiotics. If there is a collection of pus, it should be drained out and the wound should be cleaned.

Summary

Cellulitis is a very common occurrence in which acute inflammation occurs due to entry of pathogens. It usually persists for a few hours to a few days. Some common organisms causing cellulitis are:

• Staphylococcus aureus
• Streptococcus
• Pseudomonas
• Neisseria
• Legionella

By a 3 day course of antibiotics, the infection is usually resolved, unless it has extensively spread, in which case, the duration of treatment increases.

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2. Simon MS, Cody RL. Cellulitis after axillary lymph node dissection for carcinoma of the breast. Am J Med. Nov 1992;93(5):543-8.

3. Daum RS. Clinical practice. Skin and soft-tissue infections caused by methicillin-resistant Staphylococcus aureus. N Engl J Med. Jul 26 2007;357(4):380-90.

4. Roberts S, Chambers S. Diagnosis and management of Staphylococcus aureus infections of the skin and soft tissue. Intern Med J. Dec 2005;35 Suppl 2:S97-105.

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7. Brown T. Recurrent Cellulitis: Penicillin Effective for Prevention. Medscape Medical News, May 1, 2013. Available at http://www.medscape.com/viewarticle/803476. Accessed May 8, 2013.

8. Lamagni TL, Darenberg J, Luca-Harari B, et al. Epidemiology of severe Streptococcus pyogenes disease in Europe. J Clin Microbiol. Jul 2008;46(7):2359-67

9. Chuang YC, Yuan CY, Liu CY, Lan CK, Huang AH. Vibrio vulnificus infection in Taiwan: report of 28 cases and review of clinical manifestations and treatment. Clin Infect Dis. Aug 1992;15(2):271-6.

10. Lederman ER, Weld LH, Elyazar IR, et al. Dermatologic conditions of the ill returned traveler: an analysis from the GeoSentinel Surveillance Network. Int J Infect Dis. Nov 2008;12(6):593-602.