Bacterial Osteomyelitis or Nonbacterial Osteitis in Children: A Study Involving the German Surveillance Unit for Rare Diseases in Childhood

Cachexia, chorea, and pain in chronic nonbacterial osteitis and inflammatory bowel disease: a case report

BACKGROUND

Inflammatory bowel disease is an inflammatory disorder that primarily impacts the gastrointestinal tract, leading to malnutrition and chronic microscopic intestinal blood loss. Uncontrolled systemic inflammation can impact other parts of the body, known as extraintestinal manifestations. Up to 25% of patients with inflammatory bowel disease are reported to have these complications in their skin, joints, bones, eyes, liver, lung, and pancreas (Rogler et al. in Gastroenterology 161(4):1118-1132, 2021). Neurologic involvement as extraintestinal manifestations are less common, reported at 3-19%, including neuropathies, demyelination, and cerebrovascular events (Morís in World J Gastroenterol. 20(5):1228-1237, 2014).

CASE PRESENTATION

A 13-year-old Caucasian boy presented with 1 month of progressive lower-extremity pain, weakness, and weight loss. His physical examination was notable for cachexia, lower-extremity weakness, and chorea. Labs revealed normocytic anemia and systemic inflammation. Imaging revealed symmetric abnormal marrow signal in the pelvis and upper femurs. Pathologic examination of the bone revealed chronic inflammation consistent with chronic nonbacterial osteitis. Endoscopy revealed colonic inflammation consistent with inflammatory bowel disease.

CONCLUSIONS

Children and adolescents with musculoskeletal pain lasting more than 2 weeks with systemic signs or symptoms like weight loss should prompt evaluation for systemic inflammatory disorders such as chronic nonbacterial osteitis, which can occur in isolation or associated with inflammatory bowel disease. This patient also had a nonspecific neurologic abnormality, chorea, which resolved with treatment of underlying inflammatory disorder. These extraintestinal manifestations may be concurrent with or precede intestinal inflammation, requiring a high index of suspicion when investigating nonspecific systemic inflammation.

Transcriptome analysis based on machine learning reveals a role for autoinflammatory genes of chronic nonbacterial osteomyelitis (CNO)

Chronic nonbacterial osteomyelitis (CNO) is an autoinflammatory bone disorder. The origin and development of CNO involve many complex immune processes, resulting in delayed diagnosis and a lack of effective treatment. Although bioinformatics analysis has been utilized to seek key genes and pathways in CNO, only a few bioinformatics studies that focus on CNO pathogenesis and mechanisms have been reported. This study aimed to identify key biomarkers that could serve as early diagnostic or therapeutic markers for CNO. Two RNA-seq datasets (GSE133378 and GSE187429) were obtained from the Gene Expression Omnibus (GEO). Weighted gene coexpression network analysis (WGCNA) and differentially expressed gene (DEG) analysis were conducted to identify the genes associated with CNO. Then, the autoinflammatory genes most associated with CNO were identified based on the GeneCards database and a CNO prediction model, which was created by the LASSO machine learning algorithm. The accuracy of the model and effects of the autoinflammatory genes according to receiver operating characteristic (ROC) curves were verified in external datasets (GSE7014). Finally, we performed clustering analysis with ConsensusClusterPlus. In total, eighty CNO-related genes were identified and were significantly enriched in the biological processes regulation of actin filament organization, cell-cell junction organization and gamma-catenin binding. The main enriched pathways were adherens junctions, viral carcinogenesis and systemic lupus erythematosus. Two autoinflammatory genes with high expression in CNO samples were identified by combining an optimal machine learning algorithm (LASSO) with the GeneCards database. An external validation dataset (GSE187429) was utilized for ROC analysis of the prediction model and two genes, and the results indicated good efficiency. Then, based on consensus clustering analysis, we found that the expression of UTS2 and MPO differed between clusters. Finally, the ceRNA network of lncRNAs and the small molecule compounds targeting the two autoinflammatory genes were predicted. The identification of two autoinflammatory genes, the HCG18/has-mir-147a/UTS2/MPO axis and signalling pathways in this study can help us understand the molecular mechanism of CNO formation and provides candidate targets for the diagnosis and treatment of CNO.

How Have the Diagnosis and Treatment of Chronic Recurrent Multifocal Osteomyelitis Changed Over Time?

PURPOSE

Chronic recurrent multifocal osteomyelitis (CRMO) is a rare inflammatory condition characterized by sterile bone lesions. There appears to be a shift in the diagnostic modalities and treatment over the past decades despite insufficient published data. The purpose of this study was to document: 1) the number of patients diagnosed with CRMO, 2) patient demographics, 3) disease characteristics at presentation, 4) diagnostic modalities employed, and 5) treatments prescribed at our institution over a 30-year period.

METHODS

This single-center, retrospective cohort study included children diagnosed with CRMO who presented between 1990 and 2020. The electronic medical records were queried using numerous search terms. Patients were excluded if CRMO was included in the differential diagnosis but was not confirmed at the time of chart review or if CRMO was suspected early in the disease course but the patient was ultimately diagnosed with another condition. The predictor (time in years) and outcome variables (diagnostic modalities and treatment types) were tested using bivariate analyses using IBM SPSS, Version 27 (IBM Corp., Armonk, NY).

RESULTS

A total of 224 patients were diagnosed with CRMO during the observation period (68.3% female; 67.4% white). The number of patients diagnosed over the past decade rose by 215%, as compared to the previous 2 decades (1990 to 2010). Regional magnetic resonance imaging (83.8%) and biopsy (66.5%) were the most utilized diagnostic modalities over the past decade, with a statistically significant decline in the proportion of biopsies performed (66.5% during the past decade vs 84.9% in the previous 2 decades, P = .01). Over the past decade, nonsteroidal anti-inflammatory drugs (40.1%), disease-modifying antirheumatic drugs (27.1%), and tumor necrosis factor inhibitors (21.1%) were the most commonly used treatments, with a statistically disproportionate increase in the use of tumor necrosis factor inhibitors (21.1% during the past decade vs 3.8% in the previous 2 decades, P < .001).

CONCLUSIONS

This is one of the largest CRMO cohort studies and the only study to observe changes in diagnostic modalities and treatment over a 30-year period. Future studies should assess the impact of variations in clinical presentation, time to diagnosis, diagnostic modalities, and management as predictors of disease outcomes.

Nonbacterial and bacterial osteomyelitis in children: a case-control retrospective study

Purpose

Osteomyelitis is a group of bone infectious (bacterial osteomyeilitis-BO) and noninfectious inflammatory diseases (nonbacterial osteomyelitis-NBO) with similar clinical, radiology, and laboratory features. Many patients with NBO are misdiagnosed as BO and receive unnecessary antibiotics and surgery. Our study aimed to compare clinical and laboratory features of NBO and BO in children, to define key discriminative criteria, and to create an NBO diagnostic score (NBODS).

Methods

The retrospective multicenter cohort study included clinical, laboratory, and instrumental information about histologically confirmed NBO (n = 91) and BO (n = 31). The variables allowed us to differentiate both conditions used to construct and validate the NBO DS.

Results

The main differences between NBO and BO are as follows: onset age-7.3 (2.5; 10.6) vs. 10.5 (6.5; 12.7) years (p = 0.03), frequency of fever (34.1% vs. 90.6%, p = 0.0000001), symptomatic arthritis (67% vs. 28.1%, p = 0.0001), monofocal involvement (28.6% vs. 100%, p = 0.0000001), spine (32% vs. 6%, p = 0.004), femur (41% vs. 13%, p = 0.004), foot bones (40% vs. 13%, p = 0.005), clavicula (11% vs. 0%, p = 0.05), and sternum (11% vs. 0%, p = 0.039) involvement. The following four criteria are included in the NBO DS: CRP ≤ 55 mg/l (56 points), multifocal involvement (27 points), femur involvement (17 points), and neutrophil bands ≤ 220 cell/μl (15 points). The sum > 17 points allowed to differentiate NBO from BO with a sensitivity of 89.0% and a specificity of 96.9%.

Conclusion

The diagnostic criteria may help discriminate NBO and BO and avoid excessive antibacterial treatment and surgery.

Increasing Cases of Chronic Nonbacterial Osteomyelitis in Children: a series of 215 cases from a single tertiary referral center

Objective

Chronic non-bacterial osteomyelitis (CNO) is a rare autoinflammatory bone disease that is gaining recognition from clinicians and researchers. We aim to publish data from our cohort of CNO patients living in the northwestern United States to increase the awareness of specific demographics, characteristics, and presentation of this rare disease.

Methods

A retrospective chart review was performed of our electronic medical records. Patients with complete chart records that met criteria for a diagnosis of CNO from 2005-2019 were included. Extracted data including patient demographics, bone biopsy results, and lesion locations on advanced imaging were analyzed. King County census data were used to calculate the annual new case rate within our center.

Results

A total of 215 CNO cases were diagnosed at our large tertiary pediatric hospital. The majority of cases were of Caucasian descent residing in Washington's most populous county, specifically, in King County. Most cases were diagnosed in 2016-2019, showing a significant increase in the annual case rate from 8 to 23 per million children in King County, though there did not appear to be a seasonal predilection. Biopsy rate decreased from 75% to 52%. 152 (71%) children had family history of autoimmunity. With increasing use of whole-body MRI, results demonstrated that 68% had multiple lesions.

Conclusion

CNO has been diagnosed at an increased rate in recent years. Whole-body MRI may assist in identifying other lesions that may be asymptomatic on presentation. Bone biopsy is still required in some children at time of diagnosis.

Chronic Nonbacterial Osteomyelitis: Insights into Pathogenesis, Assessment, and Treatment

Chronic nonbacterial osteomyelitis, or its most severe form, chronic recurrent multifocal osteomyelitis, is an autoinflammatory bone disease that causes skeletal inflammation characterized by bone pain and swelling that primarily affects children. It is a diagnosis of exclusion and its clinical presentation may mimic underlying infectious processes and malignancy. Clinical suspicion for this diagnosis and timely referral to pediatric rheumatology is crucial to achieve earlier diagnosis, appropriate treatment, and improved quality of life of affected patients and families. This article focuses on recent insights into the pathogenesis of chronic nonbacterial osteomyelitis and outlines recent advances and ongoing research.

Clinical Practice Guideline by the Pediatric Infectious Diseases Society and the Infectious Diseases Society of America: 2021 Guideline on Diagnosis and Management of Acute Hematogenous Osteomyelitis in Pediatrics

This clinical practice guideline for the diagnosis and treatment of acute hematogenous osteomyelitis (AHO) in children was developed by a multidisciplinary panel representing Pediatric Infectious Diseases Society (PIDS) and the Infectious Diseases Society of America (IDSA). This guideline is intended for use by healthcare professionals who care for children with AHO, including specialists in pediatric infectious diseases, orthopedics, emergency care physicians, hospitalists, and any clinicians and healthcare providers caring for these patients. The panel's recommendations for the diagnosis and treatment of AHO are based upon evidence derived from topic-specific systematic literature reviews. Summarized below are the recommendations for the diagnosis and treatment of AHO in children. The panel followed a systematic process used in the development of other IDSA and PIDS clinical practice guidelines, which included a standardized methodology for rating the certainty of the evidence and strength of recommendation using the GRADE (Grading of Recommendations Assessment, Development and Evaluation) approach. A detailed description of background, methods, evidence summary and rationale that support each recommendation, and knowledge gaps can be found online in the full text.

Chronic nonbacterial osteomyelitis (CNO) and chronic recurrent multifocal osteomyelitis (CRMO)

Chronic nonbacterial osteomyelitis (CNO) is an inflammatory bone disorder that most frequently affects children and adolescents. Chronic recurrent multifocal osteomyelitis (CRMO) is a severe form of CNO, usually characterized by symmetrical inflammatory bone lesions and its waxing and waning character. Sometimes severe and chronic pain can significantly affect the quality of life and psychosocial development of individuals affected. In the absence of prospectively tested and widely accepted diagnostic criteria or disease biomarkers, CNO remains a diagnosis of exclusion, and infections, malignancy and other differentials require consideration (1). The pathophysiology of CNO is not fully understood, but imbalanced cytokine expression and increased inflammasome activation in monocytes from CNO patients contribute to a pro-inflammatory phenotype that contributes to bone inflammation (2). Currently, no medications are licensed for the use in CNO. Most patients show at least some response to nonsteroidal anti-inflammatory drugs, others require more aggressive treatment that can include corticosteroids, cytokine-blocking agents and/or bisphosphonates (3). While under the care of an experienced team and sufficient treatment, the prognosis is good, but some patients will develop sequalae which can include vertebral compression fractures (1).

•

CNO is an autoinflammatory bone disorder mostly affecting children and adolescents.

•

Dysregulated cytokine expression and pathological activation of inflammasomes play a central role.

•

Treatment is based on experience from case series and expert consensus treatment plans.

•

Understanding the exact molecular pathophysiology will allow patient stratification and individualized treatment.

Similarities and Differences between Clavicular Bacterial Osteomyelitis and Nonbacterial Osteitis: Comparisons of 327 Reported Cases

Background

Currently, both clavicular bacterial osteomyelitis (BO) and nonbacterial osteitis (NBO) remain not well understood owing to their much lower incidences. This study is aimed at summarizing similarities and differences between clavicular BO and NBO based on comparisons of literature-reported cases.

Methods

We searched the PubMed and Embase databases to identify English published literature between January 1^st, 1980, and December 31^st, 2018. Inclusion criteria were studies evaluating clinical features, diagnosis, and treatment of clavicular BO and NBO, with eligible data for synthesis analysis.

Results

Altogether, 129 studies with 327 patients were included. Compared with BO, clavicular NBO favored females (P < 0.001) and age below 20 years (P < 0.001) and mostly presented in a chronic phase (disease term exceeding 2 months) (P < 0.001). Although local pain and swelling were the top two symptoms for both disorders, fever, erythema, and a sinus tract were more frequently found in BO patients (P < 0.01). Although they both favored the medial side, lesions in the clavicular lateral side mostly occurred in BO patients (P = 0.002). However, no significant differences were identified regarding the serological levels of white blood cell count (P = 0.06), erythrocyte sedimentation rate (P = 0.27), or C-reactive protein (P = 0.33) between BO and NBO patients before therapy. Overall, the BO patients achieved a statistically higher cure rate than that of the NBO patients (P = 0.018).

Conclusions

Females, age below 20 years, and a long duration of clavicular pain and swelling may imply NBO. While the occurrence of a sinus tract and lesions in the lateral side may be clues of BO, inflammatory biomarkers revealed limited values for differential diagnosis. BO patients could achieve a better efficacy than the NBO patients based on current evidence.

Osteoperiostitis in children: proposal for a diagnostic algorithm

Juvenile osteoperiostites (JOP) are a group of inflammatory bone diseases whose differential diagnosis is often difficult. The main conditions are acute osteomyelitis (AOM), chronic non-bacterial osteomyelitis (CNO) and the Goldbloom syndrome (GS). The study was aimed to develop an algorithm to enable an early diagnosis of JOP. Clinical records of patients with AOM, CNO and GS, followed at our Center over the past 10 years, were reviewed. Twelve additional patients with GS were selected from PubMed/MEDLINE literature search. Data collected included demographics, clinical manifestations, laboratory and instrumental investigations at disease onset. The association between categorical variables was investigated, and the segmentation of patients with different diagnoses was analyzed through a classification tree model (CTREE package) in order to build up a diagnostic algorithm. Ninety-two patients (33 CNO, 44 AOM, 15 GS) entered the study. Among 30 variables considered at onset, nine (age at onset, fever, weight loss, symmetry, focality, functional limitation, anemia, elevated ESR, CRP) resulted statistically significant in differentiating the three clinical entities from each other and were chosen to build up a decisional tree. Three variables, symmetry of bone involvement, presence of fever and age at disease onset, resulted significant to discriminate each of the three diseases from the others. The performance of the diagnostic algorithm was validated by comparing the diagnoses provided by the model with the real diagnoses and showed 85.9% accuracy.Conclusion: We propose a diagnostic algorithm, based on simple clinical data, which can help guide a prompt and appropriate diagnosis of JOP. What is Known: • Juvenile osteoperiostitis (JOP) are a group of inflammatory bone diseases followed by various pediatric specialists. • The distinction between these conditions is not easy as clinical and laboratory features often overlap. What is New: • We propose a diagnostic algorithm, based on clinical data of real patients, with high degree accuracy. • This instrument can help guide the prompt and appropriate diagnosis of JOP.

Chronic nonbacterial osteomyelitis - clinical and magnetic resonance imaging features

BACKGROUND

Chronic nonbacterial osteomyelitis (CNO) is a rare autoinflammatory bone disorder. Little information exists on the use of imaging techniques in CNO.

MATERIALS AND METHODS

We retrospectively reviewed clinical and MRI findings in children diagnosed with CNO between 2012 and 2018. Criteria for CNO included unifocal or multifocal inflammatory bone lesions, symptom duration >6 weeks and exclusion of infections and malignancy. All children had an MRI (1.5 tesla) performed at the time of diagnosis; 68 of these examinations were whole-body MRIs including coronal short tau inversion recovery sequences, with additional sequences in equivocal cases.

RESULTS

We included 75 children (26 boys, or 34.7%), with mean age 10.5 years (range 0-17 years) at diagnosis. Median time from disease onset to diagnosis was 4 months (range 1.5-72.0 months). Fifty-nine of the 75 (78.7%) children presented with pain, with or without swelling or fever, and 17 (22.7%) presented with back pain alone. Inflammatory markers were raised in 46/75 (61.3%) children. Fifty-four of 75 (72%) had a bone biopsy. Whole-body MRI revealed a median number of 6 involved sites (range 1-27). Five children (6.7%) had unifocal disease. The most commonly affected bones were femur in 46 (61.3%) children, tibia in 48 (64.0%), pelvis in 29 (38.7%) and spine in 20 (26.7%). Except for involvement of the fibula and spine, no statistically significant differences were seen according to gender.

CONCLUSION

Nearly one-fourth of the children presented with isolated back pain, particularly girls. The most common sites of disease were the femur, tibia and pelvic bones. Increased inflammatory markers seem to predict the number of MRI sites involved.

Clinical characteristics and treatment of clavicular osteomyelitis: a systematic review with pooled analysis of 294 reported cases

BACKGROUND

It is usually difficult to diagnose clavicular osteomyelitis (OM), and treatment is delayed because of its rarity. This study aimed to summarize clinical characteristics and treatment of this disease.

METHODS

We searched the PubMed and Embase databases to identify English studies that reported on clavicular OM from January 1980 through December 2016. Effective data were pooled for analysis.

RESULTS

In total, 111 studies comprising 294 cases (bacterial OM, 146; nonbacterial OM, 148) were included, with a sex ratio of 1.89:1 indicating female predilection. Overall, the median age at diagnosis was 16 years. The acute to chronic phase ratio was 0.30, with a median symptom duration of 4 months. The most frequently reported symptom was pain (192 cases), followed by swelling (151 cases) and fever (52 cases). Altogether, 86.94% cases of single-site involvement were reported, with the medial side being the most common site (69.95%). The erythrocyte sedimentation rate achieved the highest positive rate (74.44%) before treatment. The total positive rate of culture for bacterial OM was 81.82%, with Staphylococcus aureus being the most frequently detected pathogen (44.70%). The average cure rate was 83.52%, with no significant difference between surgical (89.70%) and nonsurgical (79.63%) cases (P = .079).

CONCLUSIONS

Clavicular OM, predominant in female patients and young people, usually occurred at a chronic stage. Pain was the most frequent symptom, with the medial side being the most involved site. The erythrocyte sedimentation rate may be a helpful indicator for diagnosis. Regardless of surgery or nonsurgery, most patients achieved a favorable prognosis.

Nationwide epidemiologic study for pediatric osteomyelitis and septic arthritis in South Korea: A cross-sectional study of national health insurance review and assessment service

Epidemiologic studies of pediatric bone and joint infection have been done mostly by developed Western countries, and such results could be expected to be biased. Therefore, an epidemiologic study to identify the distinct features of an Eastern country would be beneficial to improve their health outcomes and to reduce health care cost. A study was planned to investigate the epidemiology of pediatric osteomyelitis and septic arthritis in South Korea and to find out epidemiologic factors related with the occurrence of surgery.We conducted a cross-sectional study among hospitalized pediatric patients (<18 years old) with osteomyelitis and septic arthritis using nationwide cohort based on the Health Insurance Review and Assessment Service (HIRA) from 2008 to 2016. Percentage of hospitalization was additionally calculated according to several epidemiologic factors including age, month, site of infection, and region of residence. Logistic regression analysis was performed to find out the association between epidemiologic factors and occurrence of surgeryAnnual hospitalization rates (per 100,000) in our country were 7.8 to 9.1 for osteomyelitis, and 11.9 to 20.8 for septic arthritis. Frequent sites of osteomyelitis and septic arthritis were pelvis and lower extremity. The hospitalization rates of osteomyelitis and septic arthritis showed increasing trend with age. After multivariate logistic regression analysis, female gender, children, and adolescents rather than infants, rural area rather than urban area were associated with significantly increased odd ratios for surgery.The hospitalization rate of septic arthritis (11.9 to 20.8 per 100,000) in South Korea was higher than the Western countries (1.1 to 11 per 100,000), and the hospitalization rate of osteomyelitis (peak at 12 years) and septic arthritis (peak at 17 years) showed increasing trend with age, which was different from those of the developed Western countries showing higher incidence in children aged under 5 years. After multivariate logistic regression analysis, our study identified female gender, higher age group including children, and adolescents, and rural residence as epidemiologic risk factors associated with surgery.

The role of real-time PCR testing in the investigation of paediatric patients with community-onset osteomyelitis and septic arthritis

BACKGROUND

Culture yield in osteomyelitis and septic arthritis is low, emphasising the role for molecular techniques.

AIMS

The purpose of this study was to review the laboratory investigation of childhood osteomyelitis and septic arthritis.

METHODS

A retrospective review was undertaken in an acute tertiary referral paediatric hospital from January 2010 to December 2016. Cases were only included if they had a positive culture or bacterial PCR result from a bone/joint specimen or blood culture, or had radiographic evidence of osteomyelitis.

RESULTS

Seventy-eight patients met the case definition; 52 (66%) were male. The median age was 4.8 years. Blood cultures were positive in 16 of 56 cases (29%), with 11 deemed clinically significant (Staphylococcus aureus = 8, group A Streptococcus = 3). Thirty-seven of 78 (47%) bone/joint samples were positive by culture with S. aureus (n = 16), coagulase-negative Staphylococcus (n = 9) and group A Streptococcus (n = 4), being the most common organisms. Sixteen culture-negative samples were sent for bacterial PCR, and four were positive (Kingella kingae = 2, Streptococcus pneumoniae = 1, group A Streptococcus = 1).

CONCLUSIONS

Sequential culture and PCR testing can improve the detection rate of causative organisms in paediatric bone and joint infections, particularly for fastidious microorganisms such as K. kingae. PCR testing can be reserved for cases where culture is negative after 48 h. These results have been used to develop a standardised diagnostic test panel for bone and joint infections at our institution.

Chronic non-bacterial osteitis from the patient perspective: a health services research through data collected from patient conferences

OBJECTIVE

Although chronic non-bacterial osteitis (CNO) is an ever-increasingly recognised illness in the paediatric community and the adult healthcare community, a study to assess diagnosing, treatment and the psychosocial aspect of CNO from a large population pool was not available. We aimed to investigate CNO from the patient perspective.

DESIGN

Health services research, patient survey.

SETTING

Ludwig-Maximilians-University (LMU) Pediatric Rheumatology Department CNO Conferences held in June 2013 and June 2015.

PARTICIPANTS

Using a patient survey developed by the LMU Pediatric Rheumatology Department, 105 patients from ages 5 to 63 years were assessed regarding CNO to include epidemiological data, medical history and treatment, initial symptoms, diagnostic procedures, current symptoms, associated diseases, current treating physicians, absences in school and work due to illness and the impact of illness on patient, family and friends.

RESULTS

Active CNO was reported in 90% of patients present, with 73% being women and 27% being men. An overwhelming majority (70%) reported being diagnosed within 18 months of onset of symptoms; however, the initial diagnoses were wide-ranged to include malignancies in 36% to bacterial osteomyelitis in 30%, where the majority were treated with an antibiotic and/or were biopsied. When asked about the psychosocial aspect of this illness, 83% reported that non-bacterial osteitis (NBO) negatively impacted the family, 79% reported that NBO has negatively affected either school or work and 56% reported a negative impact on friendships.

CONCLUSION

Delay of diagnosis, living with differential diagnoses like malignancies and finding specialists for medical care are a few examples of what leads patients into searching for more information. The negative impact on daily life including family relationships, friendships and work/school highlights a need for better psychosocial support such as guidance counselling or psychological support due to three-quarters of patients receiving no such said support.

Treatment of Staphylococcus aureus Infections

Staphylococcus aureus, although generally identified as a commensal, is also a common cause of human bacterial infections, including of the skin and other soft tissues, bones, bloodstream, and respiratory tract. The history of S. aureus treatment is marked by the development of resistance to each new class of antistaphylococcal antimicrobial drugs, including the penicillins, sulfonamides, tetracyclines, glycopeptides, and others, complicating therapy. S. aureus isolates identified in the 1960s were sometimes resistant to methicillin, a ß-lactam antimicrobial active initially against a majority S. aureus strains. These MRSA isolates, resistant to nearly all ß-lactam antimicrobials, were first largely confined to the health care environment and the patients who attended it. However, in the mid-1990s, new strains, known as community-associated (CA-) MRSA strains, emerged. CA-MRSA organisms, compared with health care-associated (HA-) MRSA strain types, are more often susceptible to multiple classes of non ß-lactam antimicrobials. While infections caused by methicillin-susceptible S. aureus (MSSA) strains are usually treated with drugs in the ß-lactam class, such as cephalosporins, oxacillin or nafcillin, MRSA infections are treated with drugs in other antimicrobial classes. The glycopeptide drug vancomycin, and in some countries teicoplanin, is the most common drug used to treat severe MRSA infections. There are now other classes of antimicrobials available to treat staphylococcal infections, including several that have been approved after 2009. The antimicrobial management of invasive and noninvasive S. aureus infections in the ambulatory and in-patient settings is the topic of this review. Also discussed are common adverse effects of antistaphylococcal antimicrobial agents, advantages of one agent over another for specific clinical syndromes, and the use of adjunctive therapies such as surgery and intravenous immunoglobulin. We have detailed considerations in the therapy of noninvasive and invasive S. aureus infections. This is followed by sections on specific clinical infectious syndromes including skin and soft tissue infections, bacteremia, endocarditis and intravascular infections, pneumonia, osteomyelitis and vertebral discitis, epidural abscess, septic arthritis, pyomyositis, mastitis, necrotizing fasciitis, orbital infections, endophthalmitis, parotitis, staphylococcal toxinoses, urogenital infections, and central nervous system infections.