Invasive Mycobacterium chimaera Infections and Heater–Cooler Devices in Cardiac Surgery

摘要

To the Editor: In their recent assessment of Mycobacterium chimaera risk in patients undergoing heart valve surgery, Sommerstein et al. compare their findings to our prior risk assessment for UK patients (1,2). In their article, the authors note their assessed risk as “4 to 7” times higher than our risk estimate and suggest this relates to differences in case-finding methodology. Our study reported incidence density (cases per 10,000 person-years) to account for the differing lengths of postoperative follow-up in each successive annual cohort of surgical patients. In contrast, Sommerstein et al. calculated crude risk based on annual procedure numbers. Since our published assessment was undertaken some years before the authors’ assessment, additional cases have been diagnosed, in keeping with the long incubation period for these infections, a median of 15 months but up to 5 years (3). Recalculation of risk and 95% (binomial) CIs, limited to 2008–2014 to match the authors’ assessment, would yield a crude risk estimate of 0.24 (0.15–0.35) per 1,000 procedures (24/102,234); the risk in Switzerland (11/14,054) would be estimated at 0.78 (0.39–1.40), just over 3 times higher.