Causes of Necrotizing Fasciitis & Risk Factors

Necrotizing fasciitis (NF), or the ‘flesh-eating bug’ as it tends to be known in the press, is an extremely rapidly progressing infection that is difficult to manage and can lead to significant morbidity and mortality.

Risk Factors of Necrotizing Fasciitis

While anyone with an infection may, in theory, develop NF, in practice the majority of patients with NF (82%) have an immunosuppressive condition such as diabetes mellitus or renal insufficiency,¹ have a history of alcohol abuse,¹ or are taking immunosuppressive drugs for cancer.² Diabetes mellitus seems to be one of the greatest risk factors for the disease, with 57% of NF patients in one study reported to be diabetic.³ Approximately half of all the patients contracting NF have a history of skin injury, while 25% have experienced blunt trauma.³ Infections originating in the deep tissues or bones are also a likely source of the disease, as the infection may progress rapidly with no outward visible signs, reaching a critical stage before becoming apparent.² Although the condition can strike an individual of any age, incidence appears to increase with age, and is also more common in men.³

Causes of Necrotizing Fasciitis

Most cases of NF are bacterial in nature, with other organisms such as fungi being responsible only in rare cases.² Bacterial NF is usually subdivided into two categories. Type I disease can be described as a synergistic polymicrobial infection involving both aerobic and non-anaerobic bacteria and streptococci species other than serogroup A.^4,5 Infection by non-anaerobic bacteria  leads to tissue hypoxia, encouraging subsequent colonization and infection by anaerobic organisms which exacerbates the infection and contributes to its rapid spread.² In contrast, type II NF is a monomicrobial infection only, involving group A streptococci (GAS) bacteria.^4,5 Type I disease tends to occur in individuals with some form of immunosuppression or chronic disease, while type II disease can occur in any individual of any age and even in the absence of any medical complications.⁴

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References

1. Cheung JPY, Fung B, Tang WM, Ip WY. A review of necrotising fasciitis in the extremities. Hong Kong Med J 2009; 15: 44-52
2. MedicineNet.com. Necrotizing fasciitis. Available from http://www.medicinenet.com/necrotizing_fasciitis/article.htm
3. Hung CC, Chang                SC, Lin SF. Clinical manifestations, microbiology  and  prognosis  of 42  patients with  necrotizing  fasciitis. J Formos Med Assoc 1996; 95: 917-22
4. Shimizu T and Tokuda Y. Necrotizing fasciitis. Inter Med 2010; 49: 1051-1057
5. Black JM, Black SB. Surgical wounds, tubes, and drains. In: Baranoski S, Ayello EA, eds. Wound Care Essentials: Practice Principles. 2^nd Edition. Lippincott Williams & Wilkins, Ambler PA. 2008.