Nosocomial Transmission of Severe Acute Respiratory Syndrome: Better Quality of Evidence Is Needed

Abstract

To the Editor—We would like to comment on the article by Yu et al. [1] regarding the risk factors for nosocomial outbreaks of severe acute respiratory syndrome that occurred in some hospital wards and not in others. The authors performed a retrospective case-control study at the ward level and found that several environmental or administrative factors and host factors, such as oxygen therapy or bilevel positive airway pressure ventilation, were associated with the occurrence of these outbreaks. We wish to discuss the study's most important methodological flaws, which may invalidate the results, and to emphasize some points that should be taken into consideration in future studies.