Background: Monofocal necrotizing fasciitis (MONF) involves a single site in a rapidly progressing infection and necrosis of the fascia and surrounding soft tissue. Synchronous multifocal necrotizing fasciitis (SMNF), the simultaneous development of NF in multiple noncontiguous sites, is rarely reported. This study aimed to compare the clinical characteristics and outcomes between patients with SMNF and MONF, and to determine the risk factors of SMNF. Methods: Our retrospective case-control study compared the clinical characteristics and outcomes, between January 2006 and January 2013, of patients with SMNF and of patients with MONF of the extremities. Results: We enrolled 144 patients with NF of the extremities: 19 with SMNF and 125 with MONF. The duration of symptoms before admission was significantly shorter for the former than for the latter (1.7 days vs. 3.3 days, p = 0.001); the prevalence of shock at the initial visit significantly higher (73.7% vs. 36%, p = 0.002); and the total-case postoperative mortality rate significantly higher (68.4% vs. 14.4%, p < 0.001). In further analysis of the total-case mortality, 9 in 13 SMNF deaths (69.2%) within 7 days after fasciotomy were in the majority while 13 with 28-day mortality (72.2%) was the majority of MONF deaths (p < 0.001). SMNF was significantly more likely to involve bacteremia (89.5% vs. 36%, p < 0.001). Independent risk factors for SMNF were liver cirrhosis (LC) (odds ratio [OR] 6.0, p = 0.001) and end-stage renal disease (ESRD) (OR 7.1, p = 0.035). Gram-negative bacteria were most common in SMNF, and Gram-positive bacteria in MONF (83.3% vs. 53.3%, p = 0.005). Vibrio species were the most common single microbial cause (35.4%) of all NF patients and were the overwhelming cause (73.7%) of SMNF. Staphylococcus aureus and group A β-hemolytic streptococcus (45.6%) were the other predominant causes of MONF while both (10.5%) rarely caused multifocal NF. Conclusions: SMNF was more fulminant than was MONF. SMNF was attributable primarily to marine Gram-negative bacteria. Physicians should be aware of SMNF because of its extremely high mortality rate.
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