Streptococcal necrotizing fasciitis and the dermatologist

Necrotizing fasciitis was probably first described by Joseph Jones, a Confederate army surgeon. It may be caused by a number of infective organisms, either in isolation or as polymicrobial infections; about 10% of cases are streptococcal (type II necrotizing fasciitis). The high mortality from this infection, and use of terms such as ‘killer bug disease’ or ‘flesheating bacteria’ has generated intense media attention, although analysis of individual cases in apparent outbreaks, such as the UK cases in 1994, often demonstrates that they were due to different organisms or different streptococcal serotypes. However, 10–15% of cases of necrotizing fasciitis are nosocomial and outbreaks of streptococcal infections on dermatological wards have been described. Old age, diabetes, cancer, immunosuppression, chronic skin sepsis, trauma and extensive surgery all predispose to polymicrobial necrotizing fasciitis. By contrast, about 50% of cases of streptococcal necrotizing fasciitis occur in young and previously fit individuals. Accepting a degree of media hype, there is an apparent true increase in virulence of streptococci, and descriptions of new streptococcal diseases such as streptococcal toxic shock syndrome, recalcitrant erythematous desquamating disorder and recurrent toxin-mediated perineal erythema have appeared in the last two decades. Lack of immunity in a cohort who have not been exposed to virulent streptococci has been proposed as an explanation, and an association of invasive group A streptococcal disease with lack of exotoxin antibodies has been demonstrated, but immunization with exotoxin before infection in a mouse model was actually associated with poorer survival. Bacterial factors which affect the severity of streptococcal infections include surface protein expression and production of toxins. The M-1 and M-3 surface proteins increase adherence of streptococci to tissues and protect against phagocytosis by neutrophils. Streptococcal pyrogenic exotoxins (SPE-A, B and C) are directly toxic and (especially SPE-A and SPE-B) are commonly produced by strains of streptococci which cause necrotizing fasciitis. They also, along with streptococcal superantigen (SSA), act as superantigens and lead to cytokine release manifested by clinical symptoms such as hypotension. In a large Canadian study, most cases of streptococcal necrotizing fasciitis had either M1 (35%) or M3 (25%) surface proteins and possessed either the spe-A (40%) or spe-C (30%) gene. Although none of these affected prognosis in this group of patients, poor prognosis has been associated with some specific streptococcal strains. Most cases of streptococcal necrotizing fasciitis are group A infections, but group B has also been reported. The involvement of dermatologists with necrotizing fasciitis has largely been with diagnosis and presurgical management. However, the potential for dermatologists to inadvertently act as a source of infection is described in the case reported in this issue by Gibbon and Bewley (p. 717), in which the patient died after infection of a surgical wound with streptococcus of the same serotype that was subsequently demonstrated in the throat swab of the asymptomatic surgeon. Necrotizing fasciitis has also been described following procedures such as liposuction, surgical or laser blepharoplasty, injection of botulinum toxin, and other injections or needlestick injuries. Although these do not all reflect infection from the surgeon, pharyngeal infections are a probable reservoir for invasive streptococcal clones and dermatologists do need to be aware of this risk. Other cases which might present to dermatologists include those which occur as a complication of varicella, zoster, pilonidal sinus or paronychia, as well as the commoner problem of patients in whom the onset is difficult to distinguish from cellulitis. Features which suggest the possibility of necrotizing fasciitis rather than cellulitis include rapid progression, poor response to adequate doses of an appropriate antibiotic, blistering, necrosis, cyanosis, extreme tenderness, high fever, tachycardia, hypotension and altered conscious level; however, many of the local signs can occur in the oedematous elderly lower leg with ordinary cellulitis. Newer diagnostic tests which may be useful to confirm streptococcal infection include rapid streptococcal diagnostic kits, PCR of exotoxin genes such as spe-B and identification by immunofluorescence in tissue sections. A deep biopsy with frozen sections may distinguish necrotizing fasciitis from cellulitis by demonstration of a dense neutrophilic infiltrate in fascia and deep subcutaneous tissue. Magnetic resonance imaging, especially using a T2 weighted scan, is a good method for identifying fasciitis but the sensitivity of this technique exceeds the specificity. The mortality due to streptococcal necrotizing fasciitis is 30–50% but can be significantly improved by early diagnosis, thorough surgical excision of affected tissue, intensive general supportive measures and appropriate antibiotic treatment; clindamycin is preferable to penicillin when there is a significant bacterial load. Older age, bacteraemia (present in 50%), hypotension and associated streptococcal toxic shock syndrome all adversely affect the prognosis. Newer therapeutic possibilities include protease inhibitors and antioxidants, for which there is strong in vitro support. Intravenous immunoglobulin may opsonize streptococci expressing M-1 protein and neutralize superantigen activity, although administration of antibodies to SPE-A in a mouse model did not increase survival. There may therefore be an British Journal of Dermatology 1999; 141: 613–616.

Field of study: Medicine