eLife assessment
This study provides a potentially useful assessment of the effect of testing contacts of cases in school classes when identified, rather than at the end of quarantine, on both the number of secondary infections and other outcomes including tracing delay and identification of the possible source of infection. The authors find that the intervention likely led to a decrease in tracing delay and an increase in the number of possible sources of infection, though were unable to determine whether secondary transmission decreased, due in part to unmeasured confounding. While the surveillance system described provides a solid dataset appropriate for this analysis, the description of methods, study outcomes, and consideration of potential confounding factors is incomplete.