Read an interesting study in JHI with a novel design that I thought I’d share. The study team evaluated the scale of COVID-19 outbreaks across three hospitals in Wales based on characteristics of the ward. When controlling for the things that you think might predict the scale of COVID-19 outbreaks (like speciality, number of toilets, patient age), the thing that came out as the biggest drive of outbreak size was how many patient transfers occurred into the ward. This suggests that the advice from “central command” to minimise patient moves made sense, and still makes sense to reduce the risk of transmissible infectious diseases in our hospitals.

I remember in our early COVID-19 outbreaks at Imperial observing that these outbreaks were spreading across patient pathways, and not just wards. Commonly, several wards are linked together in common flow – for example, patients have a complex elective procedure, are admitted to ICU, stepped down to HDU stepped down to the ward, then to a rehab ward, and then discharged. Patients often move up and down these pathways as their clinical need requires. When we first looked how to make sense of COVID-19 transmission dynamics in hospitals, this came out strongly in the patterns of transmission that we noted.

Today’s study looked at COVID-19 outbreaks across three hospitals in Wales, and ran a case-control study. The ‘cases’ were the wards with big outbreaks (>9 patients with SARS-CoV-2 identified >7 days after hospital admission within a 28 day period), and the ‘controls’ were wards with small outbreaks. In the multivariable analysis, the only variable that came out as significant was the number of inpatient transfers into the ward. Key factors that were not significant included ward size, speciality, staffing level, or number of isolation cubicles. The type and efficacy of ventilation on the ward was not assessed, which is a shame!

So, what does this tell us? Well, it suggests that the driving factor of COVID-19 outbreak scale was the number of inpatients transferred into the ward (different from the number of admissions to the ward). This suggests that when patients who had been elsewhere in the hospital accumulating increased risk of contracting SARS-CoV-2 infection were aggregated together, this elevated the risk of outbreaks. Part of this is an unavoidable consequence of necessary pathways across multiple wards. But part of this is an avoidable culture of unnecessary patient transfers, which we’d do well to address!