Introduction: Methicillin-sensitive staphylococcus aureus (MSSA) has been the predominant aetiological agent in acute osteomyelitis (AHO) in children. Recent studies from the United States have demonstrated an increase in community-acquired Methicillin-resistant Staphylococcus aureus (CA-MRSA) infections, which have been linked to increased morbidity.

Aim: a) to compare the patterns of AHO including the incidence of CA-MRSA in two tertiary children’s hospitals in Canada (The Hospital for Sick Children) and the United Kingdom (Southampton General Hospital) respectively, b) to compare the clinical course of MSSA versus CA-MRSA AHO in children in these two institutions.

Method: A retrospective review was carried out of all children up to 16 years, who were diagnosed with AHO at both centres over a five-year period. Demographic information, diagnostics, aetiology, treatment and outcomes was collected for comparison across both institutions and between MSSA and CA-MRSA identified patients.

Results: 99 cases of AHO were identified in Toronto (HSC) and 82 cases in Southampton (SGH) over the given time frames. The male: female ratios were 1.5:1 at HSC and 1.7:1 at SGH. The most commonly identified organism at both sites was MSSA, representing 42% of cultures at HSC and 22% at SGH. 2 Cases of CA-MRSA were identified at HSC, while 1 case was identified in Southampton, confirmed to be PVL-positive. No cases of Haemophilus influenzae were identified at either site. There were no significant differences in the median lengths of stay, rates of operative intervention, or complications between the two institutions. CA-MRSA cases were on average younger (7.5 yrs vs 9 yrs) and were all girls, compared with 32% girls in the MSSA group. CA-MRSA patients had similar initial laboratory profiles with the MSSA patients, except for significantly higher C-Reactive Proteins (200 vs 64) (p < 0.05). CA-MRSA patients experienced a significantly longer hospital stay (23 vs 8 days); were more likely to undergo surgical intervention (2/3 vs 34/59); were treated with longer duration of IV antibiotics (34 days vs 10.5 days); and longer total duration of antibiotics (61 days vs 46 days). 1/3 CA-MRSA patients required admission to the ICU for sepsis

Conclusions: MSSA remains the predominant aetiological agent in AHO at two large children’s hospitals in Canada and the UK. The patterns of infection are similar at both sites. CA-MRSA AHO infections have been identified at both centres, and although these remain uncommon, they are associated with a more severe clinical course. One can expect the incidence of CA-MRSA strains to rise, necessitating increased vigilance.