WASHINGTON (Reuters) -U.S. worker productivity dropped at a faster pace than initially thought in the first quarter, driving labor costs sharply higher at a time when businesses are already facing rising costs from tariffs on imported goods. Nonfarm productivity, which measures hourly output per worker, decreased at a 1.5% annualized rate last quarter, the Labor Department's Bureau of Labor Statistics said on Thursday. Economists polled by Reuters had forecast the decline in productivity would be unrevised at a 0.8% rate.