To the Editor: Assiri et al. (Aug. 1 issue)(1) provide valuable information about a hospital outbreak of Middle East respiratory syndrome coronavirus (MERS-CoV) infection. However, the authors do not describe the infection-control measures used in the hospital, and they do not discuss the possibility of aerosol transmission of MERS-CoV, a coronavirus similar to the severe acute respiratory syndrome coronavirus (SARS-CoV). MERS-CoV can cause severe or fatal disease, and there is no prophylaxis or specific treatment. If the form of transmission is not understood, health care professionals should adhere to the precautionary principle that reasonable steps to reduce risk should not ...