National accounting and consulting firm BDO USA LLP will acquire Carlsbad-based CEA LLP next month, expanding BDO’s staff to about 90 and making it the fifth-largest accounting firm in the county, the companies announced.

BDO, with an office in La Jolla, will absorb all 31 CEA partners and staff. The national firm said CEA’s deep presence in North County would help BDO expand its geographic reach in San Diego. BDO was previously the 11th-largest firm in the region.

“We are a very successful firm and combining with BDO will allow us to amplify what we’ve built,” CEA founding partner Thomas Applegate said. “Our clients will have access to a wider array of services, extensive industry experience and the resources of BDO’s extensive global network.”

BDO’s assurance managing partner in San Diego, Lee Duran, said CEA’s skills in the restaurant, manufacturing and wholesale distribution industries would help BDO expand its subject specializations.

“They also have a strong tax planning and consulting team with an ability to handle family-owned businesses,” Duran said. “In San Diego, we were a bit more focused on corporate.”

BDO has entered 20 new cities and expanded its workforce in 11 others over the past three years, largely through mergers. The CEA deal is expected to close Dec. 1.