Airbnb Inc. says it’s banning “party houses” in the wake of a deadly shooting at an Airbnb rental in California. In a series of tweets Saturday, Airbnb co-founder and CEO Brian Chesky said that the San Francisco-based company is stepping up efforts to “combat unauthorized parties and get rid of abusive host and guest conduct.” Chesky said Airbnb is expanding manual screening of “high risk” reservations that are flagged by its system.