eMedicine Specialties > Infectious Diseases > Skin and Soft-Tissue Infections
Cellulitis
Updated: Sep 23, 2009
Introduction
Background
Cellulitis refers to an inflammatory process caused by bacterial infection of the dermis and underlying subcutaneous tissues of the skin. A local and systemic host immune response leads to signs of inflammation in the affected tissue.
Pathophysiology
The human integument provides a very effective barrier against environmental pathogens. Squamous epithelial cells, with their tight intercellular bonds, are the first line of defense against the outside environment. When this barrier is breached owing to trauma or underlying dermatitis, bacteria are able to penetrate to the deeper dermis, where infection occurs. Bacteria commonly found on the skin are most often the cause of cellulitis, although bacteria from the environment may also cause disease.
Frequency
United States
Recent evidence suggests that the incidence of cellulitis is increasing in the United States. Outpatient visits for cellulitis increased from 32 to 48 per 1000 population from 1997 to 2005.1
International
The frequency of cellulitis is unknown.
Mortality/Morbidity
The vast majority of cellulitis and soft-tissue infections can be treated on an outpatient basis with oral antibiotics and do not result in lasting sequelae. However, just as the incidence of cellulitis is increasing, so is the severity. Although the exact reason for this is unknown, certain host and pathogen factors play a role in increasing the risk of severe infection.
Perhaps the most important contribution to the increasing severity of cellulitis is the emergence of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA), specifically the USA 300 clone, as a leading pathogen in cellulitis and soft-tissue infections associated with purulence.2 Infections caused by CA-MRSA tend to be more severe and are resistant to many of the antibiotics commonly used to treat cellulitis.
This is a case of cellulitis without associated purulence. Note the presence of lymphedema, a risk factor for cellulitis (photo courtesy of Amy Williams).
Patient with cellulitis of the left ankle. Note the area of drainage. This cellulitis was caused by community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA). (Photo courtesy of Texas Dept. of Public Health)
Abscess and associated cellulitis caused by community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA). (Photo courtesy of Texas Dept. of Public Health)
Hand cellulitis caused by community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA). (Photo courtesy of Texas Dept. of Public Health)
Certain strains of bacteria, most notably group A beta-hemolytic Streptococcus (GABHS) and S aureus, produce toxins. These toxins may mediate a more severe systemic infection, leading to septic shock and death.3,4
Certain host factors predispose to severe infection. Individuals with comorbid conditions such as diabetes mellitus, immunodeficiency, cancer, venous stasis, chronic liver disease, peripheral arterial disease, and chronic kidney disease appear to be at a higher risk for both recurrent and more severe infection owing to an altered host immune response. Concurrent intravenous or subcutaneous “skin popping” drug use also predisposes to cellulitis. Infections in this setting are most often polymicrobial, but CA-MRSA is also a common pathogen.
Race
Cellulitis has no predilection for any race or ethnic group.
Sex
Cellulitis has no predilection for either sex.
Age
In general, no specific age group is at a higher risk for cellulitis. However, certain age groups are at a higher risk in some unique scenarios.
- Historically, buccal cellulitis caused by Haemophilus influenzae type B was more common in children younger than age 3 years. Vaccination against this organism may have decreased the incidence of this infection, but recent data suggest that this remains something to be considered, even in vaccinated cohorts.5
- Facial cellulitis is more common in adults older than 50 years.
- Perianal cellulitis, usually with GABHS, occurs in children younger than 3 years.
- Group B Streptococcus cellulitis occurs in infants younger than 6 months. Underlying osteomyelitis or septic arthritis must be excluded in these infants.
- Elderly patients with cellulitis are predisposed to thrombophlebitis.
Clinical
History
A comprehensive history is vital to diagnosing cellulitis. The patient may or may not relate an episode of trauma that has preceded their symptoms. Cellulitis develops several days after the inciting trauma; this intervening period often means that the patient does not recollect any trauma, which is often minor, at the time of presentation. Rapid progression is concerning sign of a more severe infection, such as necrotizing fasciitis, and should be managed promptly.
- If the patient recalls an episode of trauma, the clinician should ask about circumstances surrounding the incident that may elicit clues to a particular etiology. Identifying the specific inciting cause helps the clinician to identify the most likely pathogen, to choose appropriate antibiotic therapy, and to offer appropriate immunization, if indicated.
- The presence of foreign bodies, including indwelling intravenous catheters, external orthopedic pins, and other surgical devices, predisposes to infection in the local area.
- The patient should also be questioned about the presence of other skin disorders, including various types of dermatitis and especially preceding fungal infection, which serve as a portal of entry for bacterial pathogens.6
- The past medical history should focus on the presence of comorbid conditions that increase the risk for cellulitis, the most common of which include diabetes mellitus, HIV infection/AIDS, chronic kidney disease, and chronic liver disease.
- The surgical history may include a recent surgery that resulted in wound infection. Alternatively, a remote surgical history involving lymph node dissection or venotomy continues to predispose to cellulitis, even years after the surgery, owing to resultant edema.7
Physical
The physical examination should first focus on the area of concern. Most skin and soft-tissue infections have the 4 cardinal signs of infection: erythema, pain, swelling, and warmth. Several physical examination findings may help the clinician to identify the most likely pathogen and to assess the severity of the infection, facilitating appropriate treatment.
- Skin infection without underlying drainage, penetrating trauma, eschar, or abscess is most likely caused by streptococci. On the other hand, S aureus, often CA-MRSA, is the most likely pathogen when these factors are present.8
- Lymphangitic spread (red lines streaking away from the area of infection), crepitus, and hemodynamic instability are indications of severe infection, requiring more aggressive treatment.
- Circumferential cellulitis or pain that is disproportional to examination findings should prompt consideration of more severe soft-tissue infection.
Causes
The most common cause of cellulitis is infection with gram-positive cocci, specifically GABHS and S aureus, whether it be MRSA or methicillin-sensitive S aureus (MSSA). In certain circumstances, organisms such as anaerobes, gram-negative bacteria, and fungi may also cause cellulitis.
Some unique clinical situations to be aware of include the following:
- Individuals with diabetes are predisposed to skin infection. Infections in these patients are often polymicrobial. Common cellulitis pathogens, S aureus and streptococci, are still common in such patients.9
- Mammalian bite wounds represent a specific subset of cellulitis with unique pathogens. These infections are usually polymicrobial.10 Human, dog, cat, and wild-animal bites all predispose to cellulitis with unique pathogens, but dogs are the most commonly encountered bite wound in both the primary care and emergency setting.11 Several organisms are of particular interest in animal bites, including the following:10
- Capnocytophaga canimorsus (dog)
- Eikenella corrodens (human)
- Pasteurella multocida (dog or cat)
- Streptobacillus moniliformis (rat)
- Vibrio vulnificus may cause cellulitis following a traumatic injury in brackish or salt water. Individuals with chronic liver disease are particularly susceptible to V vulnificus infections.12
- Cellulitis in infants is usually caused by hematogenous spread of group B Streptococcus. These patients often have additional sites of infection, such as the blood, joints, bone, kidneys, or central nervous system.
- Immunocompromised individuals are at an increased risk for gram-negative or fungal cellulitis.
- Cellulitis occurring around surgical wounds less than 24 hours postoperatively may result from GABHS or Clostridium perfringens infection. C perfringens produces gas, which may be appreciated on examination as crepitus.
- Puncture wounds, especially through the bottom of athletic shoes, may cause Pseudomonas osteomyelitis and/or cellulitis.
- Mycobacterium marinum is an atypical mycobacterium that is ubiquitous in aquatic environments and usually inoculates humans after fish-tank exposure.13
More on Cellulitis |
Overview: Cellulitis |
| Differential Diagnoses & Workup: Cellulitis |
| Treatment & Medication: Cellulitis |
| Follow-up: Cellulitis |
| Multimedia: Cellulitis |
| References |
| Next Page » |
References
Hersh AL, Chambers HF, Maselli JH, Gonzales R. National trends in ambulatory visits and antibiotic prescribing for skin and soft-tissue infections. Arch Intern Med. Jul 28 2008;168(14):1585-91. [Medline].
King MD, Humphrey BJ, Wang YF, Kourbatova EV, Ray SM, Blumberg HM. Emergence of community-acquired methicillin-resistant Staphylococcus aureus USA 300 clone as the predominant cause of skin and soft-tissue infections. Ann Intern Med. Mar 7 2006;144(5):309-17. [Medline].
Bisno AL, Cockerill FR 3rd, Bermudez CT. The initial outpatient-physician encounter in group A streptococcal necrotizing fasciitis. Clin Infect Dis. Aug 2000;31(2):607-8. [Medline].
Francis JS, Doherty MC, Lopatin U, Johnston CP, Sinha G, Ross T. Severe community-onset pneumonia in healthy adults caused by methicillin-resistant Staphylococcus aureus carrying the Panton-Valentine leukocidin genes. Clin Infect Dis. Jan 1 2005;40(1):100-7. [Medline].
Cieslak TJ, Rajnik M, Roscelli JD. Immunization against Haemophilus influenzae type B fails to prevent orbital and facial cellulitis: results of a 25-year study among military children. Mil Med. Oct 2008;173(10):941-4. [Medline].
Björnsdóttir S, Gottfredsson M, Thórisdóttir AS, Gunnarsson GB, Ríkardsdóttir H, Kristjánsson M, et al. Risk factors for acute cellulitis of the lower limb: a prospective case-control study. Clin Infect Dis. Nov 15 2005;41(10):1416-22. [Medline].
El Saghir NS, Otrock ZK, Bizri AR, Uwaydah MM, Oghlakian GO. Erysipelas of the upper extremity following locoregional therapy for breast cancer. Breast. Oct 2005;14(5):347-51. [Medline].
Busch BA, Ahern MT, Topinka M, Jenkins JJ 2nd, Weiser MA. Eschar with cellulitis as a clinical predictor in community-acquired MRSA skin abscess. J Emerg Med. Jul 8 2008;[Medline].
Lipsky BA. New developments in diagnosing and treating diabetic foot infections. Diabetes Metab Res Rev. May-Jun 2008;24 Suppl 1:S66-71. [Medline].
Brook I. Microbiology and management of human and animal bite wound infections. Prim Care. Mar 2003;30(1):25-39, v. [Medline].
Dendle C, Looke D. Review article: Animal bites: an update for management with a focus on infections. Emerg Med Australas. Dec 2008;20(6):458-67. [Medline].
Dechet AM, Yu PA, Koram N, Painter J. Nonfoodborne Vibrio infections: an important cause of morbidity and mortality in the United States, 1997-2006. Clin Infect Dis. Apr 1 2008;46(7):970-6. [Medline].
Aubry A, Chosidow O, Caumes E, Robert J, Cambau E. Sixty-three cases of Mycobacterium marinum infection: clinical features, treatment, and antibiotic susceptibility of causative isolates. Arch Intern Med. Aug 12-26 2002;162(15):1746-52. [Medline].
[Guideline] Stevens DL, Bisno AL, Chambers HF, Everett ED, Dellinger P, Goldstein EJ, et al. Practice guidelines for the diagnosis and management of skin and soft-tissue infections. Clin Infect Dis. Nov 15 2005;41(10):1373-406. [Medline].
Tayal VS, Hasan N, Norton HJ, Tomaszewski CA. The effect of soft-tissue ultrasound on the management of cellulitis in the emergency department. Acad Emerg Med. Apr 2006;13(4):384-8. [Medline].
Schmid MR, Kossmann T, Duewell S. Differentiation of necrotizing fasciitis and cellulitis using MR imaging. AJR Am J Roentgenol. Mar 1998;170(3):615-20. [Medline].
Zahar JR, Goveia J, Lesprit P, Brun-Buisson C. Severe soft tissue infections of the extremities in patients admitted to an intensive care unit. Clin Microbiol Infect. Jan 2005;11(1):79-82. [Medline].
Edlich RF, Cross CL, Dahlstrom JJ, Long WB 3rd. Modern Concepts of the Diagnosis and Treatment of Necrotizing Fasciitis. J Emerg Med. Dec 10 2008;[Medline].
Hepburn MJ, Dooley DP, Skidmore PJ, Ellis MW, Starnes WF, Hasewinkle WC. Comparison of short-course (5 days) and standard (10 days) treatment for uncomplicated cellulitis. Arch Intern Med. Aug 9-23 2004;164(15):1669-74. [Medline].
Moran GJ, Krishnadasan A, Gorwitz RJ, Fosheim GE, McDougal LK, Carey RB, et al. Methicillin-resistant S. aureus infections among patients in the emergency department. N Engl J Med. Aug 17 2006;355(7):666-74. [Medline].
Cenizal MJ, Skiest D, Luber S, Bedimo R, Davis P, Fox P, et al. Prospective randomized trial of empiric therapy with trimethoprim-sulfamethoxazole or doxycycline for outpatient skin and soft tissue infections in an area of high prevalence of methicillin-resistant Staphylococcus aureus. Antimicrob Agents Chemother. Jul 2007;51(7):2628-30. [Medline].
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. [Medline].
Stryjewski ME, Chambers HF. Skin and soft-tissue infections caused by community-acquired methicillin-resistant Staphylococcus aureus. Clin Infect Dis. Jun 1 2008;46 Suppl 5:S368-77. [Medline].
Davis SL, McKinnon PS, Hall LM, Delgado G Jr, Rose W, Wilson RF. Daptomycin versus vancomycin for complicated skin and skin structure infections: clinical and economic outcomes. Pharmacotherapy. Dec 2007;27(12):1611-8. [Medline].
Krige JE, Lindfield K, Friedrich L, Otradovec C, Martone WJ, Katz DE. Effectiveness and duration of daptomycin therapy in resolving clinical symptoms in the treatment of complicated skin and skin structure infections. Curr Med Res Opin. Sep 2007;23(9):2147-56. [Medline].
Byl B, Clevenbergh P, Jacobs F, Struelens MJ, Zech F, Kentos A. Impact of infectious diseases specialists and microbiological data on the appropriateness of antimicrobial therapy for bacteremia. Clin Infect Dis. Jul 1999;29(1):60-6; discussion 67-8. [Medline].
Falagas ME, Vergidis PI. Narrative review: diseases that masquerade as infectious cellulitis. Ann Intern Med. Jan 4 2005;142(1):47-55. [Medline].
Cox NH. Oedema as a risk factor for multiple episodes of cellulitis/erysipelas of the lower leg: a series with community follow-up. Br J Dermatol. Nov 2006;155(5):947-50. [Medline].
Further Reading
Keywords
cellulitis, gram-positive bacteria, group A beta-hemolytic Streptococcus, GABHS, Staphylococcus aureus, S aureus, MRSA, methicillin-resistant Staphylococcus aureus, CA-MRSA, community-acquired MRSA, Streptococcus pyogenes, S pyogenes, systemic toxins, bacteremia, sepsis, buccal cellulitis, Haemophilus influenzae type B, HIB, facial cellulitis, perianal cellulitis, group B Streptococcus cellulitis, Pseudomonas osteomyelitis, septic arthritis, thrombophlebitis, Pasteurella multocida, P multocida, Vibrio vulnificus, V vulnificus, Aeromonas species, Clostridium perfringens, C perfringens, crepitus, crepitation, Escherichia coli cellulitis, E coli, septic shock













Overview: Cellulitis