Childhood osteomyelitis-incidence and differentiation from other acute onset musculoskeletal features in a population-based study

Abstract

Background: Osteomyelitis can be difficult to diagnose and there has previously not been a prospective approach to identify all children in a defined geographic area. The aim of this study was to assess the annual incidence of osteomyelitis in children, describe the patient and disease characteristics in those with acute (< 14 days disease duration) and subacute osteomyelitis (> or = 14 days disease duration), and differentiate osteomyelitis patients from those with other acute onset musculoskeletal features.

Methods: In a population-based Norwegian study physicians were asked to refer all children with suspected osteomyelitis. Children with osteomyelitis received follow-up at six weeks, six months and thereafter as long as clinically needed.

Results: The total annual incidence rate of osteomyelitis was 13 per 100,000 (acute osteomyelitis 8 and subacute osteomyelitis 5 per 100,000). The incidence was higher in patients under the age of 3 than in older children (OR 2.9, 95%: CI 2.3-3.7). The incidence of non-vertebral osteomyelitis was higher than the incidence of vertebral osteomyelitis (10 vs. 3 per 100 000; p = .002). Vertebral osteomyelitis was more frequent in girls than in boys (OR 7.0, 95%: CI 3.3-14.7). ESR > or = 40 mm/hr had the highest positive predictive laboratory value to identify osteomyelitis patients at 26% and MRI had a positive predictive value of 85%. Long-bone infection was found in 16 (43%) patients. ESR, CRP, white blood cell count, neutrophils and platelet count were higher for patients with acute osteomyelitis than for patients with subacute osteomyelitis. Subacute findings on MRI and doctor's delay were more common in subacute osteomyelitis than in acute osteomyelitis patients. Blood culture was positive in 26% of the acute osteomyelitis patients and was negative in all the subacute osteomyelitis patients.

Conclusion: The annual incidence of osteomyelitis in Norway remains high. ESR values and MRI scan may help to identify osteomyelitis patients and differentiate acute and subacute osteomyelitis.

Figure 1

Flow chart showing recruitment of children with osteomyelitis. JIA- Juvenile Idiopathic Arthritis; SLE – Systemic Lupus Erythematosus.

Figure 2

ROC curves of laboratory tests used during the first visit to discriminate between patients with osteomyelitis (n = 37) and patients without osteomyelitis (n = 392). The curves plot the relationship between the true positive rate (Sensitivity, y-axis) and the false positive rate (1 - Specificity, x-axis) at different cut-off titers. The higher the cut-off titer that is chosen, the lower the sensitivity and the higher the specificity, and visa versa. The diagonal reference line (area under curve (AUC) = .5), indicates no discrimination. The greater the distance of the curve from the diagonal, the higher the overall discriminative ability of the test.

Figure 3

Age on admission of patients with acute osteomyelitis (n = 24) and subacute osteomyelitis (n = 13).