The analysed data represents about 325 million individual accounts held in trusts that were created by credit card issuers in order to sell the debt to investors — similar to how many banks packaged and sold subprime mortgage loans. Together, they account for about 45 per cent of the $920 billion the US Federal Reserve counts as credit card debt owed by Americans.

Until recently, US credit card default rates had been running close to record lows, providing one of the few profit growth areas for US banks, which continue to flood Americans’ mailboxes with billions of letters monthly offering easy sign-ups for new plastic. Even after the recent spike in bad loans, the credit card business is still quite lucrative, thanks to interest rates that can run as high as 36 per cent, plus late fees and other penalties.

But what is coming into sharper focus from the detailed monthly SEC filings from the trusts is a snapshot of the worrisome state of Americans’ ability to juggle growing and expensive credit card debt.

Many economists expect delinquencies and defaults to rise further after the holiday shopping season. Mark Zandi, chief economist and co-founder of Moody’s Economy.com Inc, cited mounting mortgage problems that began after this summer’s subprime financial shock as one of the culprits, as well as a weakening job market in the Midwest, South and parts of the West, where real-estate markets have been particularly hard hit.

“Credit card quality will continue to erode throughout next year,” he said. Economists also cite America’s long-standing attitude that debt — even high-interest credit card debt — is no big deal.