MGM Resorts International /zigman2/quotes/209932643/composite MGM -3.31% said it will require that all guests wear face masks inside public spaces at all of its U.S. outlets effective Friday, as it moves to upgrade safety measures during the coronavirus pandemic. Previously, the casino operator only required employees to wear masks. The U.S. recorded a one-day total of 34,700 new confirmed COVID-19 cases on Wednesday, the highest level since late April, when the number peaked at 36,400, according to data aggregated by Johns Hopkins University. Infections are rising in 29 states, according to a New York Times tracker. "It is clear that the coronavirus still presents a significant public health threat, and masks have proven to be one of the best ways to curtail the spread," MGM said in a statement. "We want guests and employees to feel comfortable that we are putting their health and safety first." MGM shares were down 2.2% premarket and have fallen 49% in the year to date, while the S&p 500 /zigman2/quotes/210599714/realtime SPX +0.77% has fallen 6%.