Timing of surgery following SARS-CoV-2 infection: an international prospective cohort study.

We thank the authors for their work [1], which attempted to answer a fundamental question in the current management of surgical patients worldwide, and to quantify the risk of deciding to perform surgery on a patient previously infected with SARS‐CoV‐2. While it is fairly clear from a risk‐benefit perspective that urgent and cancer surgery should be performed promptly whenever possible despite the current pandemic, a more difficult question is how to deal with patients requiring surgery that can be deferred. This question is becoming increasingly common as countries lift their restriction policies regarding planned surgery while the pandemic is brought under control. This study strongly suggests that non‐essential surgical procedures should be postponed in patients with recent SARS‐CoV‐2 infection, including those without symptoms, in the interests of patient safety and not just because of a lack of healthcare resources.

However, we would like to point out a potential bias that does not seem to have been clearly controlled nor discussed in this study. Among the included patients with a recent infection (between 0 and 6 weeks, precisely when adjusted mortalities were highest), there was a majority of patients from low‐ and middle‐income countries (from 58.6% to 65.5%), whereas the inverse was observed for patients without infection or with an older infection (from 34.3% to 42.1%), which could have led to some excess mortality in recently infected patients. This might be supported by the observation that living in a low‐ and middle‐income country was significantly associated with higher mortality in the unadjusted analysis. Although the authors used the country income as a covariate in the logistic regression models to adjust for mortality, it would have been more appropriate to use a mixed model to separate the random effects of country income levels from the fixed effects related to patients’ conditions and their surgical procedures. This would have also provided control over possible interactions between the effects of some pre‐existing conditions on mortality and the national income level, since it can be hypothesised that some factors, such as age, may influence mortality differently depending on the country income. This is of particular concern as there appears to be an 'ecological fallacy' when looking at the aggregate data for the COVID‐19 pandemic; while high‐income countries seem to have a higher case fatality rate than low‐ and middle‐income countries at first sight [2], the individual data suggest the opposite, with higher case fatality rate among lower‐income people [3, 4]. Therefore, it does not seem appropriate to use country income as a characteristic of an individual to be used for fixed effect. It would be interesting to know whether the effect observed by the authors was consistent across country income levels, by providing a sensitivity analysis using this covariate.