Humana Inc. and UnitedHealth Group Inc. were the latest managed-care companies to announce plans to close Medicare HMO plans next year. But neither company's pullouts will affect California. Humana, the No. 2 operator of Medicare health-maintenance organizations, said it will drop coverage of 84,000 enrollees. UnitedHealth Group, the No. 2 U.S. health insurer, said it will exit Medicare in 21 counties across the country, affecting 56,000 people. The announcements bring to at least 676,000 the number of people who must find new coverage next year. The announcements come ahead of next week's deadline for companies to notify Medicare of their coverage plans for next year.