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 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.

Methods

: We reviewed our database of skin, soft tissue infections, and osteomyelitis for cases of osteomyelitis caused by

anginosus

.

Streptococcus

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

:

anginosus

Eleven patients with osteomyelitis due to

Streptococcus

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 reported.

anginosus Streptococcus anginosus

Our case series illustrates the proclivity of is rarely

Streptococcus

for associated abscess formation in the context of osteomyelitis, the need for multiple debridements to control infection, and the importance of prolonged treatment.

INTRODUCTION

The

Streptocococcus anginosus (S. anginosus)

species of streptococci.

1 bacteria which are classified group includes three within the viridans Similar to other viridans streptococci, the anginosus group often spreads hematogenously, adhering to damaged endovasculature Uniquely, and

S. anginosus

prosthetic devices, causing complications.

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 pediatric 4,5 and adult literature 6 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

INTRODUCTION ( Cont’d)

abscess.

7 As a sequela of hematogenous dissemination,

S. anginosus

has been found occasionally to infect the cervical 8 spines 9,10 as well as the iliac 11 and femur bones.

12 and lumbar Finally, isolated cases of contiguous osteomyelitis in the setting of prosthetic material 13,14 and a diabetic foot infection 15 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.

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

anginosus S.

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.

RESULTS

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 post surgical 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).

RESULTS ( Cont’d)

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 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.

Table 1.

Demographic and laboratory data for 11 cases of osteomyelitis related to

Streptococcus anginosus.

ª N=11 (No./%) ______________________________________________________________________ Demographic data Age, Mean (SD) Male Sex Comorbidities Hypertension Diabetes Smoking Peripheral arterial disease Peripheral neuropathy Coronary artery disease Cancer Chronic renal disease COPD Bisphosphonate usage Cirrhosis Route of Infection Arising contiguously Arising hematogenously Site of Infection Diabetic foot Mandible Cranium Vertebrae Laboratory WBC (cells/mm³), Mean (SD) ESR (mm/hr), Mean (SD) CRP (mg/dl), Mean (SD) Procalcitonin (ng/ml), Mean (SD) 54.8 (13.9) 7 (63.6) 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) 10 (90.9) 1 (9.1) 5 (45.5) 3 (27.3) 2 (18.2) 1 (9.1) 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. SD, standard deviation; COPD, chronic obstructive pulmonary disease; WBC, white blood cell count; ESR, erythrocyte sedimentation rate; CRP, C-reactive protein; procalcitonin; MIC, minimal inhibitory concentration.

Discussion

The present study documents 11 cases of osteomyelitis due to the

anginosus S.

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.

Future research needs to better characterize

S. anginosus

outcomes in the setting of osteomyelitis and other infections in terms of strain typing, minimal inhibitory concentrations, and serum bactericidal levels.

CONCLUSION

In conclusion, the present study documents cases of osteomyelitis due to

S. anginosus

and illustrates the virulence of this pathogen in terms of the tendency to produce bacteremia and abscess formation in the setting of osteomyelitis. Furthermore, the importance of prolonged treatment and need for extensive debridement are illustrated.

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