# A Swiss Retrospective Case Series of Pediatric Primary Subacute Hematogenous Osteomyelitis

## TL;DR

This study examines pediatric subacute osteomyelitis cases in Switzerland, highlighting the importance of MRI and NAATs for diagnosis, especially in young children.

## Contribution

The study introduces a modern diagnostic approach using NAATs and emphasizes MRI for early detection of PSAHO in toddlers.

## Key findings

- MRI is essential for diagnosing PSAHO, as radiographs have low sensitivity.
- NAATs identified or suggested a pathogen in nearly half of the cases, outperforming conventional cultures.
- Kingella kingae was the most common pathogen in children under 4 years old.

## Abstract

This study aimed to characterize the clinical spectrum and the bacteriological and microbiological etiology of pediatric primary subacute hematogenous osteomyelitis (PSAHO) and to evaluate a modern diagnostic approach for these infections. A single-center, 25-year retrospective review (2000–2025) of 107 consecutive cases of PSAHO was performed. Clinical presentation, traditional inflammatory markers, conventional cultures and nucleic acid amplification tests (NAATs) on blood, and bone and oropharyngeal samples were assessed. Most patients (73.8%) were <4 years. Fever was uncommon (15.9%), and inflammatory markers were frequently normal (white blood cell counts in 81.1%, C-reactive protein levels in 60.4%) and abnormal in 69.2% for erythrocyte sedimentation rates and in 53.8% for platelet count. Low diagnostic sensitivity of conventional blood (4.2%) and bone (25.7%) sample cultures has been reported. In contrast, a comprehensive NAAT-based approach identified or strongly suggested a pathogen in 44.9% of cases. Kingella kingae was the predominant pathogen in children under 4. Oropharyngeal PCR tests potentially identified the pathogen in another 20 cases, and its presence could be reasonably suspected in a further 68 (63.6%). MRI was essential for diagnosis, identifying all lesions, whereas the sensitivity of radiographs was low (<50%). All patients recovered completely, regardless of the management strategy. This study provides three critical advances for clinical practice: (1) PSAHO should be considered in a limping toddler even without fever or elevated inflammatory markers, and MRI is the imaging modality of choice; (2) NAATs are indispensable for etiologic diagnosis, revealing age-dependent pathogens; (3) Oropharyngeal PCR is a useful diagnostic adjunct.