The first randomised, controlled clinical trial of surgical masks compared to fit-tested and non-fit tested N95 masks in the prevention of respiratory virus infection in hospital health care workers in Beijing, China.

Intervention: Surgical masks (Arm 1), N95 masks (fit tested, Arm 2), N95 masks (not fit tested, Arm 3), Control (No masks, Arm 4) Participants will be provided with surgical masks or N95 masks, (depending on which hospital they work in) to be worn for four weeks when working on the ward. Masks will be worn when participants are working in the emergency department or respiratory ward; they will be allowed to remove the mask when: (1) they exit the department/ward; and (2) enter the tea room for meal breaks. Subjects recruited to Arm 2 will have the masks correctly fit-tested using a 3M (trademark) FT-30 Bitrex Fit Test Kit according to the manufacturers’ instructions (3M, St Paul, Minnesota (MN), USA). This kit uses a nebulized solution sprayed into an enclosed chamber and relies on the subject tasting the solution through the mask. If the subject is able to taste the solution, the mask is incorrectly fitted and needs to be re-fitted until the subject cannot taste the solution. All participants will be followed up for five weeks (which includes four weeks of wearing the masks and an extra week of non-mask wearing)