Mortality-rate comparison — what a properly-baselined reading of the cluster shows
Prosecution claim
The Crown presented the Countess of Chester 2015–2016 mortality increase as anomalous — a rise from low single-figure annual deaths in previous years to substantially more in 2015 and 2016. The jury was invited to read the rise as evidence that something beyond ordinary clinical variation was at work.
Counter-evidence
The Countess of Chester neonatal unit is a small unit, and year-on-year variation in absolute deaths is substantial just from chance. The jury was shown absolute numbers against a local historical baseline that did not adjust for acuity, admission volume, or gestation-mix. Properly baselined against national UK NICU data (the National Neonatal Research Database), against the unit's specific acuity profile (routinely admitting infants below its Level 2 designation), and against the documented outbreak, staffing and infrastructure conditions, the 2015–2016 increase is within the range of expected variation for a struggling Level 2 unit admitting a Level 3 patient mix. Dr Hannah Blencowe (LSHTM perinatal epidemiologist on the Panel) reads this as an epidemiological signal of systems failure, not of criminal pattern.
A cluster of deaths on a struggling Level 2 NICU with an outbreak, staffing strain, and acuity mismatch is what the epidemiology expects. Reading it as criminal pattern requires the systems-failure explanation to be first positively excluded. At trial, it was not.
What the jury heard
Absolute mortality numbers against a local historical baseline. Acuity, admission volume, gestation-mix, outbreak context, and staffing conditions were not systematically folded in to the statistical comparison.
What the Panel says
The Panel's case-by-case medical review implicitly incorporates the baseline-adjustment: when each deterioration is explicable by natural causes or sub-optimal clinical care, there is no residual mortality-rise anomaly requiring a criminal explanation.
What independent experts add
- The Countess of Chester was, in 2015–2016, admitting infants below its Level 2 designation.
- Level 2 units admitting Level 3 patients have substantially higher mortality than pure Level 2 mix predicts.
- The documented multi-drug-resistant bacterial outbreak on the unit raises mortality independently.
- Consultant and middle-grade staffing shortages were chronic during the cluster period.
- Sewage and plumbing failures (Mansutti defence-witness testimony) are a recognised infection-transmission route on NICUs.
- The National Neonatal Research Database is the canonical source for UK NICU outcome baselines.
- Year-on-year variation on a small unit is substantial just from chance, without any additional cause.