streptococcus agalactiae , also known as group b streptococcus ( gbs ) , is a bacterium often isolated from vaginal or rectal swab of pregnant women and long recognized as the major cause of neonatal sepsis , meningitis , and infection in pregnant women . gbs is a minor pathogen of necrotizing fasciitis ( nf ) ; however , the incidence of gbs nf in nonpregnant adults with underlying disease has increased in recent years . here , we report a case of bilateral gbs nf of the foot with a unique clinical presentation and describe the clinical characteristics of gbs nf based on a review of published cases . a 43-year - old male with a history of type 1 diabetes presented with severe pain in both feet . two weeks before our examination , he began to notice swelling and pain in the left sole , which gradually spread to his left lower leg . one week prior to presentation , the same symptoms began to emerge on his right sole and the dorsum of his right foot . the symptoms worsened , and he was admitted to our clinic because he had developed a fever of 39.2c and was unable to walk unassisted at the time of his first visit . on initial examination , he exhibited a reddish fluctuant cystic nodule on the dorsum of the right foot ( fig 1a ) , an ulcer covered with necrotic tissue on the lateral side of the right foot ( fig 1b ) , and swelling with redness on the dorsum of the left foot ( fig 1c ) . moreover , a large callus and ulcer due to diabetic peripheral neuropathy on the right sole ( fig 1d ) and streaks of necrotic skin on the left sole ( fig 1e ) were observed . laboratory analysis revealed elevated wbc ( 15,100 cells/l ) , c - reactive protein ( 22.8 mg / dl ) , blood glucose ( 434 mg / dl ) , hemoglobin a1c ( 12.2% ) and anti - gad - antibody ( 350 u / ml ) levels . computed tomography showed fluid collection , suggesting a subcutaneous abscess in the dorsum of the right foot ( fig 2a ) , and fascial thickening associated with fat stranding in both soles ( fig 2a , b ) . in addition , gas shadows were detected within the deep fascia of the right sole and left sole up to the lower leg ( fig 2a , b ) . as the gram stain of the exudate obtained from the necrotic skin of the left sole demonstrated the presence of gram - positive cocci and gram - negative rods , we suspected nf of polymicrobial origin , and the patient was empirically treated with meropenem . on the day following admission , debridement of necrotic tissues and amputation of the left fifth metatarsal bone were performed . a large amount of brownish pus was discharged from the dorsum of the right foot . necrosis of subcutaneous tissue , fascia and muscle were observed in both feet and the lower half of the left lower leg . culture of excised tissue of the left foot yielded gbs , group g streptococcus , and morganella morganii . in addition , culture of excised tissue of the right foot yielded gbs , staphylococcus aureus and pseudomonas species . furthermore , blood culture prior to administration of antibiotics yielded solely gbs . based on these findings , although debridement was repeated several times , necrosis of the fascia , muscles and bone developed in the tissues surrounding the excised parts of both feet and we were not able to control the infection . including our case , 22 cases of gbs nf in nonpregnant adults have been reported in english to date ( table 1 ) [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ] . the mean age of patients was 54 years with a male : female ratio of 7 : 15 . nf can be classified as type i nf due to a polymicrobial infection or type ii nf due to a monomicrobial infection , and the majority of gbs nf cases were type ii nf . in the 22 patients , the lower extremity was the most common site of nf , accounting for approximately 70% of cases . notably , 16 patients ( 73% ) had diabetes and 3 had cancer ( 14% ) , suggesting that an immunocompromised host is a risk factor . our case was particularly rare in that nf occurred bilaterally and there was a time lag of 1 week between the development of primary and secondary nf . bilateral nf is rare , and approximately 15 cases have been reported in english to date [ 4 , 16 , 17 , 18 , 19 ] . it can be caused by ( i ) procedures of multiple puncture , cannulation or surgery ; ( ii ) direct spreading of nf to the opposite site , and ( iii ) metastatic seeding of bacterium during the bacteremia . almost all of the reported cases , except gbs nf cases , developed bilateral nf simultaneously . regarding bilateral gbs nf , two cases of bilateral gbs nf of an extremity have been previously reported and both cases developed secondary nf after a 1-week time lag [ 4 , 16 ] . one case developed nf on the right lower leg secondary to nf of the left lower leg , and the other developed nf bilaterally on upper and lower extremities secondary to septic arthritis of the left knee . of note in both cases , secondary nf appeared at remote sites several days after debridement or amputation of the primary infected lesion , and gbs was detected in blood culture even at the start of treatment for the primary infection . thus , hematologic dissemination of gbs is an early event in the development of secondary gbs nf , and it appears that the occurrence of secondary nf with a 1-week delay is due to the slow evolution of inflammation in remote fascia and subcutaneous tissue . including cases of bilateral gbs nf of an extremity , gbs was detected in blood culture in 50% ( 11 of 22 ) of gbs nf cases . importantly , patients with positive blood culture had a high mortality rate of approximately 30% , whereas none of the patients with negative blood culture died ( table 1 ) . although it is difficult to differentiate gbs nf and gbs cellulitis because the speed of evolution of gbs nf is slow , dermatologists must be aware of the characteristics of gbs nf and the possibility of appearance of secondary nf at remote sites with an approximate 1-week delay .
necrotizing fasciitis ( nf ) is a severe bacterial infection involving fascia and subcutaneous tissue . 
 it generally affects upper or lower extremities unilaterally , and there are few reports of bilateral - extremity nf . here 
 , we report a case of a 43-year - old male with type 1 diabetes who had nf on the left foot and subsequently developed nf on the other foot 1 week later . 
 the patient survived with antimicrobial therapy and bilateral below - knee amputation . 
 as group b streptococcus ( gbs ) was isolated by blood culture and culture of excised tissues of both feet , bilateral gbs nf of the foot was diagnosed . 
 gbs is a rare causative pathogen in nf ; however , there have been two case reports of bilateral gbs nf of an extremity in which nf appeared on the opposite extremity 1 week after the primary site infection , as in our case . 
 gbs was isolated from cultures of blood and excised tissues of both extremities in both cases . 
 together , these observations suggest that gbs has a potential to cause secondary nf at remote sites by hematogenous dissemination with approximately 1 week delay and thereby lead to bilateral nf .