Employment in healthcare, the only major industry outside the federal government still adding jobs, is succumbing to the recession. In the latest sign, the president of New York City Health & Hospitals Corp. wrote to community organizations as well as employees and unions at its 11 hospitals and four nursing homes, saying the agency will lay off more workers even after slashing 400 jobs last month. More than 16 million people work in healthcare today, up from just 1% of the work force 50 years ago.