Culminating a bitter fight, thousands of Kaiser Permanente workers have decided to remain with the Service Employees International Union-United Healthcare Workers West rather than switch to a rival union.

The election results represent a major victory for SEIU-UHW and a blow to the National Union of Healthcare Workers and the powerful California Nurses Association, which recently backed NUHW in a battle that has lasted nearly three years.

The vote involved 45,500 Kaiser employees, including respiratory therapists, dietitians, housekeepers, pharmacy technicians, clerical employees, radiology technicians and other workers.

The National Labor Relations Board announced Thursday that 58 percent, or 18,844 workers voted to stay with SEIU-UHW, and 41 percent, or 13,101 favored switching to NUHW.

This was a repeat of a 2010 election in which SEIU-UHW also won by a decisive margin, but the results were later overturned when the labor board agreed with NUHW that unfair tactics were used.

Kaiser workers "know they have a strong, effective organization," said Dave Regan, president of SEIU-UHW, shortly after the results were announced. The union has negotiated contracts that set the standard for health-care workers nationwide, Regan said, and employees did not want to lose that.

In a joint statement, NUHW and CNA leaders said their rival has agreed to cutbacks in benefits for employees and won the election by exploiting workers' anxieties in a difficult economic climate. They vowed to continue their fight.

Sandy Kleffman covers health. Contact her at 510-293-2478. Follow her at Twitter.com/skleffman.