Streptococcus anginosus as a Culprit of Osteomyelitis: A Review of 11 Cases Tristan Timbrook, BA, Allen T. Griffin, MD, Julie Harting, Pharm.D, and Diana Christensen, MD Division of Infectious Diseases, University of Louisville ABSTRACT INTRODUCTION (Cont’d) RESULTS (Cont’d) Discussion Background: The Streptococcus anginosus group is comprised of three species of bacteria that are loosely classified within the viridans streptococci. Like other viridans streptococci, the anginosus group has a penchant to create hematogenous complications by adhering to damaged endovasculature and prosthetic devices. Quite distinct, however, is the proclivity for abscess formation. While a variety of sites in the human body claim anginosus as an etiologic agent of infection, osteomyelitis is unusual, particularly when not originating hematogenously. The objective of the present study was to describe a series of 11 patients with osteomyelitis due to Streptococcus anginosus in terms of demographics, comorbidities, anatomic site of infection, laboratory values, and outcomes. abscess.7 As a sequela of hematogenous dissemination, S. anginosus has been found occasionally to infect the cervical8 and lumbar spines9,10 as well as the iliac11 and femur bones.12 Finally, isolated cases of contiguous osteomyelitis in the setting of prosthetic material13,14 and a diabetic foot infection15 have been described. Given that S. anginosus as an etiology of osteomyelitis has been infrequently reported, the objective of the present study was to describe a series of patients with osteomyelitis due to S. anginosus in terms of demographics, comorbidities, anatomic site of infection, laboratory values, and course. Seventy-five percent of these cases were complicated by abscess formation while S. anginosus bacteremia was present in 30%. All anginosus isolates were sensitive to penicillin and vancomycin (Table 1). Common coinfecting pathogens were Prevotella species (42%), Bacteroides fragilis (25%), and methicillin-resistant Staphylococcus aureus (25%). The present study documents 11 cases of osteomyelitis due to the S. anginosus group. Illustrated herein is the difficulty in treating this group in the setting of osteomyelitis in terms of the need for prolonged treatment ( > 10 weeks), the need for extensive debridement (> 3 surgeries on average), even amputation, and the propensity for abscess formation and bacteremia. This study is unique given the limited literature describing the phenomenon of S. anginosus osteomyelitis. Despite the virulence illustrated here with this group of bacteria, penicillin still appears to be an effective antibiotic against these pathogens. Methods: We reviewed our database of skin, soft tissue infections, and osteomyelitis for cases of osteomyelitis caused by Streptococcus anginosus. Cases were excluded from review if no bone infections were documented. Data collected and described included patient age, comorbidities, anatomic site of infection, route of infection (hematogenous versus contiguous), inflammatory markers, confecting pathogens, susceptibility pattern of the anginosus isolate, length of treatment, and need for amputation. Results: Eleven patients with osteomyelitis due to Streptococcus anginosus were identified. All cases arose from a contiguous anatomic site, with the exception of one case that was hematogenous. Five instances were related to foot osteomyelitis while three, two, and one case, respectively, were related to mandibular, cranial, and vertebral osteomyelitis. Seventy-five percent of patients had associated abscess formation. All required extensive debridement with an average of three surgeries (SD=2.8) per patient to control infection. The mean length of antibiotic treatment was 11 weeks (SD=7.4). All anginosus isolates were sensitive to penicillin. Conclusions: Osteomyelitis due to Streptococcus anginosus is rarely reported. Our case series illustrates the proclivity of Streptococcus anginosus for associated abscess formation in the context of osteomyelitis, the need for multiple debridements to control infection, and the importance of prolonged treatment. MATERIALS AND METHODS Study Design This study was retrospective review of osteomyelitis cases in our database at the University of Louisville hospital in Louisville, KY. Instances of S. anginosus osteomyelitis were selected from 300 patients entered into the database from June 1, 2010 to August 1, 2012. Inclusion Criteria: • 18 years of age or older • Confirmed diagnosis of osteomyelitis Exclusion Criteria: • S. anginosus not identified as an infecting organism Categories of data collected in the osteomyelitis database and used for analysis were age, sex, comorbidities, site of infection, route of infection (contiguous or hematogenous), laboratory data, S. anginosus minimal inhibitory concentrations (MIC) (Table 1), presence of orthopedic hardware, presence of abscess formation, presence of S. anginosus bacteremia, coinfecting pathogens, and patient course. Factors included in patient course included length of antibiotic treatment, number of surgeries, and requirement for amputation. Statistics: Data were analyzed descriptively in terms of number (percentages), means, and standard deviations. INTRODUCTION RESULTS The Streptocococcus anginosus (S. anginosus) group includes three species of bacteria which are classified within the viridans streptococci.1 Similar to other viridans streptococci, the anginosus group often spreads hematogenously, adhering to damaged endovasculature and prosthetic devices, causing complications. Uniquely, S. anginosus has a propensity to form visceral abscesses.2 Incidence of osteomyelitis as a result of this group of organisms is quite uncommon. In a review of 186 cases of S. anginosus infection, for example, only a single case of bone infection was documented.3 Both the pediatric4,5 and adult literature6 have elucidated the rare finding of S. anginosus as an agent of cranial osteomyelitis due to abscess extension from the paranasal sinuses while other literature has documented the occurrence of mandibular osteomyelitis related to contiguous spread from an oral Eleven patients with osteomyelitis due to the S. anginosus group were identified. All 11 cases arose from a contiguous anatomic site, with the exception of a single case of hematogenous vertebral osteomyelitis that developed subsequent to gynecologic surgery. In addition to the case of vertebral osteomyelitis, five instances were related to foot osteomyelitis in the context of a progressive diabetic foot ulcer while there were three cases of mandibular osteomyelitis associated with tooth decay, bisphosphonate usage and radiation exposure, or radiation exposure alone, respectively. Finally, two instances of postsurgical cranial osteomyelitis due to S. anginosus were identified. The most common comorbidities in these patients were diabetes mellitus, hypertension, peripheral arterial disease, and peripheral neuropathy (Table 1). The average length of treatment was 10.9 weeks (SD=7.4). Each patient required an average of three surgeries (SD=2.8) to fully debride infected tissue. Four of the five foot osteomyelitis cases required partial amputations of the foot while one of the cranial osteomyelitis cases required the entire skull cap to be removed. No patients died. All patients were treated with intravenous therapy. The most common antibiotic utilized was penicillin G in dosages ranging from 24 to 30 million units per day. Future research needs to better characterize S. anginosus outcomes in the setting of osteomyelitis and other infections in terms of straintyping, minimal inhibitory concentrations, and serum bactericidal levels. CONCLUSION Table 1. Demographic and laboratory data for 11 cases of osteomyelitis related to Streptococcus anginosus.ª N=11 (No./%) ______________________________________________________________________ Demographic data Age, Mean (SD) 54.8 (13.9) Male Sex 7 (63.6) Comorbidities Hypertension Diabetes Smoking Peripheral arterial disease Peripheral neuropathy Coronary artery disease Cancer Chronic renal disease COPD Bisphosphonate usage Cirrhosis 8 (72.7) 6 (54.5) 6 (54.5) 5 (45.5) 4 (36.4) 2 (18.2) 2 (18.2) 1 (9.1) 1 (9.1) 1 (9.1) 0 (0) Route of Infection Arising contiguously Arising hematogenously 10 (90.9) 1 (9.1) Site of Infection Diabetic foot Mandible Cranium Vertebrae 5 (45.5) 3 (27.3) 2 (18.2) 1 (9.1) Laboratory WBC (cells/mm³), Mean (SD) ESR (mm/hr), Mean (SD) CRP (mg/dl), Mean (SD) Procalcitonin (ng/ml), Mean (SD) 16.4 (5.9) 75.8 (50.4) 11.5 (10.5) 2.8 (3.5) S. anginosus MIC Penicillin, Mean (SD) 0.05 (0.03) Vancomycin, Mean (SD) 0.81 (0.24) ______________________________________________________________________ ªAll values are given as No. (%) unless otherwise specified. 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