Septic arthritis with no organism: a dilemma

Performance of a diagnostic score for gouty arthritis: results from a cohort of acute arthritis suspected of being septic

Septic arthritis (SA) and gout are the main suspected etiologies of acute monoarthritis. Differentiating them is essential because SA is an emergency. The performance of a gout diagnostic score developed by Janssens et al. was investigated in a cohort of patients with acute arthritis suspected of being septic. This was an ancillary study of a single-center cohort of patients with suspected SA. Patients were classified into three groups according to the final diagnosis (gout, SA or other diagnosis). We assessed the performance of the score (sensitivity [Se], specificity [Sp], positive and negative predictive value [PPV, NPV], area under the receiver operating characteristic [ROC] curve) for the diagnosis of gouty arthritis. In total, 138 patients were included: 28 (20.3%) had gout, 42 (30.4%) SA, and 68 (49.3%) another diagnosis. The median diagnostic score was 7.0 [4.5; 8.8] for patients with gout, 3.5 [2.5; 6.0] for those with SA and 3.0 [2.0-5.0] for those with another diagnosis. With a score threshold of ≥ 8, the Se for a diagnosis of gout was 28.6%, Sp 96.4%, PPV 66.7%, and NPV 84.1%. With a threshold of ≤ 4, the Se was 82.1%, Sp 64.5%, PPV 37.1%, and NPV 93.4%. The area under the ROC for the diagnostic score was 0.79. The performance of the clinico-biological score of Janssens et al. for a diagnosis of gout applied to a cohort of patients with acute arthritis and suspected of being septic was poor. Joint aspiration remains necessary to differentiate SA from another etiology.

Changing aetiology of paediatric septic arthritis

The management of septic arthritis in children requires the prompt administration of antibiotic therapy and the identification of the causative pathogen. In the past, Staphylococcus aureus, Streptococcus pyogenes, Streptococcus pneumoniae and Haemophilus influenzae type b were considered the main causative agents of the disease, but a substantial fraction of presumptive joint infections remained unconfirmed by conventional bacteriologic cultures. In the last two decades, our knowledge of the aetiology of paediatric infectious arthritis has substantially changed as the result of the implementation of vaccination programmes against H. influenzae type b and pneumococci, and by the use of improved detection methods. In 1988, the inoculation of synovial fluid aspirates into blood culture vials revealed that Kingella kingae, a commensal member of the oropharyngeal microbiota, was the prime aetiology of skeletal system infections in children aged 6-48 months. The clinical presentation of K. kingae arthritis is subtle, and the disease is frequently missed by classic clinical and laboratory diagnostic criteria. Many children are afebrile, the acute phase reactants levels and the white blood cell counts in the blood and synovial fluid specimens are frequently normal, requiring a high clinical acumen. Increasing use of sensitive molecular methods in recent years, and particularly nucleic acid amplification tests that target K. kingae-specific genes, has further improved the detection of this elusive pathogen, demonstrated that it is responsible for 30-93% of all cases of septic arthritis below 4 years of age and reduced the fraction of culture-negative infections.

Broad-range 16 s rDNA PCR in synovial fluid does not improve the diagnostic performance of septic arthritis in native joints in adults: cross-sectional single-center study in 95 patients

OBJECTIVE

To evaluate the diagnostic performance of bacterial identification by broad-range polymerase chain reaction (PCR) of ribosomal DNA (rDNA) 16 s (16S rDNA PCR) for the diagnosis of septic arthritis on native joints.

METHODS

Patients with acute mono or oligoarthritis who underwent synovial fluid puncture and prospective follow-up allowing definitive diagnosis (septic arthritis, crystal related disease, chronic inflammatory arthritis, undifferentiated arthritis) were recruited in this single-center study. Systematic analysis of synovial fluid included leukocytes count, search for urate and pyrophosphate crystals with polarized light microscopy, direct bacteriological examination (gram staining), bacteriological culture, and 16S rDNA PCR.

RESULTS

Ninety-five patients were included, 34 of which (35.8%) had septic arthritis. Nineteen (20.0%) patients had received probabilistic antibiotic therapy prior to joint puncture. Gram + cocci infection accounted for 79.4% of septic arthritis, of which nearly half (47.1%) was caused by Staphylococcus aureus. Eight (23.5%) septic arthritis patients had a 16S rDNA PCR positive in the synovial fluid with an AUC of 0.618 (95% CI, 0.493-0.742), a sensitivity of 0.24 (95% CI, 0.12-0.40), and a specificity of 1.00 (95% CI 0.94-1.00). The diagnostic performance of 16S rDNA PCR was lower than that of direct examination (AUC at 0.691, CI 95%, 0.570-0.812), blood cultures (AUC at 0.727, CI 95%, 0.610-0.844), and culture (0.925, CI 95%, 0.856-0.994) for the diagnosis of septic arthritis. There was no difference in the positivity of 16S rDNA PCR according to previous exposure to antibiotics.

CONCLUSIONS

16 s rDNA PCR in the synovial fluid does not improve the diagnostic performance of septic arthritis on native adult joints, particularly for Gram-positive cocci infections.

Microbiological Diagnosis of Skeletal System Infections in Children

BACKGROUND

If not timely diagnosed and adequately treated, skeletal system infections in children may result in severe and permanent disability. Prompt identification of the etiology of the disease and determination of its antibiotic susceptibility are crucial for the successful management of septic arthritis, osteomyelitis, and spondylodiscitis. However, the bacteriological diagnosis of these infections has been traditionally limited by the low yield of conventional cultures and, on average, one-third of cases of pediatric joint and bone infections remained unconfirmed.

OBJECTIVE

To review the medical literature to summarize the current approach diagnosing the pediatric skeletal system infections.

METHODS

The relevant publications for the last three decades were reviewed.

RESULTS

In recent years, the detection of skeletal system pathogens has been revolutionized by the use of improved laboratory methods, including seeding of synovial fluid and bone exudates into blood culture vials, and the development and implementation of sensitive nucleic acid amplification assays. These advances have resulted in the recognition of Kingella kingae as the predominant etiology of hematogenous infections of bones, joints, intervertebral discs and tendon sheaths in children aged 6-48 months, and reduced the fraction of culture-negative osteoarthritis.

CONCLUSION

As the exudate and tissue samples obtained from young children with skeletal system infections are frequently insufficient for a comprehensive laboratory workup, physicians should take in consideration the patient's age, predisposing medical conditions and possible exposure to zoonotic organisms, and use a judicious combination of Gram's stain, culture on blood culture vials, and molecular tests to maximize the microbiological diagnosis of these diseases.

[Salmonella glenohumeral arthritis]

We report the first case of glenohumeral Salmonella arthritis in an immunocompetent 86-year-old woman. There was no entry point. An empirical antibiotherapy was started then adapted according to culture results. Given the persistence of symptoms, an arthroscopy was performed at 72 hours for a joint lavage and synovectomy. Postoperative course was good. Apyrexia was obtained by 72 hours and inflammatory syndrome was normalized in 12 days. The patient was reviewed regularly until the 3rd month. She has no clinical sequelae. Her osteoarthritis remained stable throughout follow-up.

Septic arthritis of the hip with psoas abscess caused by Non-typhi Salmonella infection in an immunocompetent patient

Osteoarticular infections caused by Non-typhi Salmonella are exceptionally encountered. We report a case of a bacteriologically documented hip infection associated with a psoas abscess due to Non-typhi Salmonella. A 64-year-old immunocompetent male was admitted in our department for pain and motion range limitation in the right hip with fever. Non-typhi Salmonella was recovered in joint fluid obtained by needle aspiration. Antimicrobial chemotherapy combined with surgical intervention was necessary for eradication of the infection. Physicians should be aware of this rare manifestation of Non-typhi Salmonella infections in non-debilitated patients.