Companies in the Standard & Poor’s 500 Index are currently the healthiest in decades, with the lowest net debt to earnings ratio in at least 24 years, $3.59 trillion in cash and marketable securities, and record earnings per share, Bloomberg News reported today. They are headed this year toward the fastest average monthly job creation since 1999, manufacturing is recovering and the U.S. has returned as an engine for global growth. The recovery, which stands in contrast to weak growth in Europe and Asia, has underpinned an almost threefold gain in the Standard & Poor’s 500 Index since March 2009. “The U.S. is leading the way — we’re the only major economy with accelerating growth,” said Mark Zandi, chief economist in West Chester, Pa., for Moody’s Analytics Inc. and a registered Democrat who has advised both the Obama administration and Senator John McCain (R). While Zandi lauds Obama’s $787 billion in stimulus spending and auto bailouts as “textbook” responses to the recession, one question for history is whether the Federal Reserve should instead get the credit. The Fed’s decision to drive down interest rates to zero allowed companies to refinance debt at lower costs, helping spur corporate growth, said Todd Lowenstein, a fund manager with San Francisco-based HighMark Capital Management Inc.