MSSA bacteraemia counts and rates of community-onset, by Sub ICB Location (SICBL) and month

Laboratory-confirmed cases of Staphylococcus aureus bacteraemia detected by blood culture confirmed resistant to any of:

• Meticillin
• Oxacillin
• Cefoxitin
• Flucloxacillin

Rationale

In January 2011 the enhanced patient-level mandatory surveillance scheme was extended to include meticillin susceptible S. aureus (MSSA) bacteraemia due to both the high national total of MSSA bacteraemias, and the observation that the strides in reducing MRSA bacteraemias had not also been seen among MSSA. It was noted that at a more local level, some organisations had reported reductions in MSSA bacteraemias and including MSSA bacteraemia in the enhanced surveillance scheme may provide details on how these reductions had been achieved, in order to replicate them elsewhere.

A low value is indicative of a low count of MSSA.

Definition of numerator

All cases of MSSA meeting the 'Definition' section above occurring for the past 11 months are summed with the current month to give a rolling 12-month total. For the calculation of rates, the past 11 months are summed with the current month and the denominator is the sum of the bed-days (for trusts) or population (for SICBLs) for the current month and preceding 11 months.

The rate for a month is then calculated by dividing the numerator by the denominator and multiplying by 100,000 to give a manageable value.

Definition of denominator

Denominator values are calculated as an annual rolling sum. For any given month, the denominator includes the value for the defined geography in the given month and the 11 preceding months.

Caveats

These data do not provide a basis for decisions on the clinical effectiveness of infection control interventions in individual Trusts: further investigations considering potential confounders would need to be undertaken before this could be done. Nor do these data provide a basis for comparisons between acute Trust or SICBLs. Rate information, using rate calculations as currently defined, is not appropriate for comparison. The counts of infections have not been adjusted to give a standardised rate considering factors such as organisational demographics or case mix. Rate information is of use for comparison of an individual organisation over time.

‘All reported cases’ refers to all MSSA-positive blood cultures reported by the Trust whose laboratory processes the specimen. It is important to note that this does not necessarily imply that the infection was acquired there. Cases that the UKHSA's HCAI Data Capture System attributes to a commissioning hub (such as the national commissioning hub, 13Q, or one of the regional Health & Justice commissioning hubs) are not featured in sub ICB Location dashboards but they do still contribute to the highest spatial level—the England national total. This means the England case total may be slightly higher than the sum of all sub ICB Location cases.