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Aim: This retrospective study's objective was to evaluate osteoarticular infection in infants less than 12 months of age, with a particular focus on biological features and bacteriological etiology. Material & methods: We retrospectively reviewed the medical records of every infant younger than 12 months old admitted in our institution for a suspected osteoarticular infection between January 1980 and December 2016. Results: Sixty-nine patients records were reviewed, including eight neonates, 16 infants from 1 to 5 months old, and 45 from 6 to 12 months old. Conclusion: Neonates and infants aged from 6 to 12 months old were more exposed to infections. Staphylococcus aureus remained the main pathogen in children <6 months, whereas Kingella kingae has become the most frequently isolated microorganism in infants aged from 6 to 12 months old.

Aims: We aimed to describe the epidemiological, biological, and bacteriological characteristics of osteoarticular infections (OAIs) caused by Kingella kingae ., Methods: The medical charts of all children presenting with OAIs to our institution over a 13-year period (January 2007 to December 2019) were reviewed. Among these patients, we extracted those which presented an OAI caused by K. kingae and their epidemiological data, biological results, and bacteriological aetiologies were assessed., Results: K. kingae was the main reported microorganism in our paediatric population, being responsible for 48.7% of OAIs confirmed bacteriologically. K. kingae affects primarily children aged between six months and 48 months. The highest prevalence of OAI caused by K. kingae was between seven months and 24 months old. After the patients were 27 months old, its incidence decreased significantly. The incidence though of infection throughout the year showed no significant differences. Three-quarters of patients with an OAI caused by K. kingae were afebrile at hospital admission, 11% had elevated WBCs, and 61.2% had abnormal CRPs, whereas the ESR was increased in 75%, constituting the most significant predictor of an OAI. On MRI, we noted 53% of arthritis affecting mostly the knee and 31% of osteomyelitis located primarily in the foot., Conclusion: K. kingae should be recognized currently as the primary pathogen causing OAI in children younger than 48 months old. Diagnosis of an OAI caused by K. kingae is not always obvious, since this infection may occur with a mild-to-moderate clinical and biological inflammatory response. Extensive use of nucleic acid amplification assays improved the detection of fastidious pathogens and has increased the observed incidence of OAI, especially in children aged between six months and 48 months. We propose the incorporation of polymerase chain reaction assays into modern diagnostic algorithms for OAIs to better identify the bacteriological aetiology of OAIs. Cite this article: Bone Joint J  2021;103-B(3):578-583.

Background: The aim of this study was to investigate changes in oropharyngeal K. kingae carriage during the first 4 y of life, including seasonal variation and comparison of asymptomatic carriage with cases of invasive osteoarticular infections (OAI)., Methods: Oropharyngeal bacterial K. kingae carriage was screened in 744 healthy children aged 7-48 mo between January 2009 and December 2012. Oropharyngeal swabs were analyzed by rt-PCR targeting the DNA of K. kingae RTX toxin, epidemiological characteristics of asymptomatic carriers and OAI case patients were recorded., Results: The carriage prevalence showed no significant difference between age groups or seasons. Compared with asymptomatic carriers, OAI cases were more likely to be aged from 7 to 12 mo (OR = 2.5; 95% CI (1.2-5.0)) and 13-24 mo (OR = 2.2; 95% CI (1.2-3.9)), and less likely over 36 mo (OR = 0.2; 95% CI (0.1-0.7)). Fewer OAI cases were identified in spring compared to asymptomatic carriers (OR = 0.3; 95% CI (0.1-0.7)), while more were detected in autumn (OR = 2.5; 95% CI (1.4-4.4))., Conclusion: Although oropharyngeal K. kingae colonization is a prerequisite for further invasive infection, this epidemiological study emphasizes that the carriage rate variations do not correlate with the variations of OAI incidence by gender, season, or age group.

Backgrounds: With the development of molecular biology and specific polymerase chain reaction, Kingella kingae has become the primary diagnosis of osteoarticular infections in young children. Clinical features of these osteoarticular infections are typically mild, and outcome is almost always favorable. We report a series of unusually severe cases of K. kingae osteoarticular infections., Methods: All patients with severe osteoarticular infections at presentation were reviewed retrospectively in 2 European pediatric centers. K. kingae was identified using real-time polymerase chain reaction in blood, fluid joint or osseous samples. Clinical, laboratory tests and radiographic data during hospitalization and follow-up were analyzed., Results: Ten children (mean age 21 ± 12 months) with severe osteoarticular infections caused by K. kingae were identified between 2008 and 2011. Diagnostic delay averaged 13.2 ± 8 days. Only 1 patient was febrile at admission, and 50% children had normal C-reactive protein values (≤10 mg/dL) at presentation. Surgical treatment was performed in all cases. Intravenous antibiotic therapy by cephalosporins for an average of 8 ± 6 days was followed by oral treatment for 27 ± 6 days. Mean follow-up was 24.8 ± 9 months, and satisfactory outcomes were reported in all cases. Two patients (20%) developed a central epiphysiodesis of the proximal humerus during follow-up, but without significant clinical consequence for the moment., Conclusions: Because of their mild clinical features at onset, diagnosis of K. kingae osteoarticular infections can be delayed. Care should be taken for early detection and treatment of these infections because bony lytic lesions and potentially definitive growth cartilage damage can occur.

The aim of this study was to evaluate the absolute risk for children younger than 4 years of age with asymptomatic oropharyngeal carriage of Kingella kingae to sustain an osteoarticular infection. The rate of K. kingae carriage in the oropharyngeal mucosa was 9% among healthy children, and the risk for an asymptomatic carrier to develop an osteoarticular infection due to K. Kingae was estimated to be lower than 1%.

Background: Kingella kingae is an emerging pathogen that may be recognized as the most common bacteria responsible for osteoarticular infections (OAI) in young children. However, its diagnosis remains a challenge and thus little evoked in infants, because K. kingae is a difficult germ to isolate on solid medium, and clinical signs are often mild. The main objective of this prospective study is to describe the clinical, biologic, and radiologic features of children with OAI caused by K. kingae. In addition, we describe the usage of a new specific real-time PCR assay in children under 4 years admitted for OAI with a probe that detects 2 independent gene targets from the K. kingae RTX toxin., Patients and Methods: All children less than 4 years admitted in our institution between January 2007 and November 2009 for suspected OAI were enrolled in this prospective study (43 cases). Age, gender, clinical signs, duration of symptoms, bone or joint involved, imaging studies, and laboratory data, including bacterial investigations, full blood count, erythrocyte sedimentation rate, and serum C-reactive protein were collected for analysis., Results: Identification of the microorganism was possible for 28 cases (65.1%) yielding K. kingae in 23 cases (82.1%). Mean age of children with K. kingae OAI was 19.6 months. Less than 15% of these patients were febrile during the admission, but 46% of them presented a history of fever-peak superior to 38.5 degrees C before admission. Thirty-nine percent of the children with K. kingae OAI had normal C-reactive protein; WBC was elevated in only 2 cases, whereas 21 patients had abnormal erythrocyte sedimentation rate, and 13 abnormal platelet counts. Direct Gram staining and classical isolation methods were negative for all cases subsequently detected as K. kingae OAI by specific real-time PCR., Conclusion: This study confirms that K. kingae is the major bacterial cause of OAI in children less than 4 years. The real-time PCR assay, specific to the K. kingae RTX toxin, provides interesting diagnostic performance when implemented in the routine microbiologic laboratory. Needless to say, a bigger cohort is required to adequately study this new qPCR assay, but the results so far seem promising. The most important additional finding is the mild-to-moderate clinical, radiologic, and biologic inflammatory response to K. kingae infection with the result that these children present few criteria evocative of OAI., Level of Evidence: II.

Kingella kingae is an emerging pathogen that is recognized as a causative agent of septic arthritis and osteomyelitis, primarily in infants and children. The bacterium is best detected by rapid inoculation in blood culture systems or by real-time PCR assays. Pathogenesis of the agent was linked recently to the production of a potent cytotoxin, known as RTX, which is toxic to a variety of human cell types. The locus encoding the RTX toxin is thought to be a putative virulence factor, and is, apparently, essential for inducing cytotoxic effects on respiratory epithelial, synovial and macrophage-like cells. Herein, we describe a novel real-time PCR assay that targets the RTX toxin gene. The assay exhibited a sensitivity of 30 c.f.u., which is 10-fold more sensitive than a previously published semi-nested broad-range 16S rRNA gene PCR, and showed no crossreactivity with several related species and common osteoarticular pathogens. Its clinical impact is illustrated by three pediatric cases.