Prices are the best gauge of vitality and the American market looks either sickly or critically ill depending on who takes its temperature. The price index from OFHEO, the watchdog of Fannie Mae and Freddie Mac, the government-sponsored mortgage lenders, shows that year-on-year prices were 1.8% higher in the third quarter—the weakest rise in 12 years, but a rise all the same. However, that measure misses sales above the $417,000 limit for regulated home loans, where prices were frothiest, as well as deals backed by subprime mortgages, where financing is now moribund.

The S&P/Case-Shiller index is a much broader measure and captures the house-price cycle rather better than the OFHEO gauge. It shows that national prices fell by 4.5% in the year to the third quarter, the biggest drop since the series started in 1987. Prices are falling even faster in large cities, according to S&P/Case-Shiller's more timely monthly index.

Further price declines seem likely given the toxic mix of blighted mortgage markets and swollen inventory. Less certain is whether the rest of the world will catch America's property flu. The Economist's quarterly round-up of global house prices suggests that American sneezing has already induced a few sniffles in other rich countries, but that emerging economies have so far proved immune.

Property markets in many parts of Europe have passed a turning-point. House-price inflation has dipped in France, Spain, Italy and Belgium. In Germany, where property values have been mostly falling since the mid-1990s, price declines have intensified over the past year. Ireland's long housing boom has turned to bust. Prices fell by almost 3% in the 12 months to September; a year earlier, house-price inflation was above 15%.

There are ominous signs of a downturn in Britain, too. Prices were nearly 7% higher in November than a year earlier, according to our preferred measure. But this still-healthy annual increase disguises a more worrying recent trend. Prices dropped by 0.8% from October, the biggest one-month decline since 1995. Data published by Halifax, Britain's biggest mortgage-lender, show that prices have fallen in each of the past three months, the worst streak for 12 years. The number of mortgages granted to homebuyers has tumbled by one-third since last year's peak.

How much the weaker trend across Europe owes to the credit squeeze is not clear. Banks reeling from credit-related losses are less willing and able to supply new mortgages. But demand for home loans was wilting even before the credit crisis, because of tighter monetary policy. Housing markets in some emerging economies, meanwhile, seem entirely unaffected. House-price inflation in South Africa remains in double digits. In Asia property values have picked up smartly in Singapore, Hong Kong and China. Even Japan looks a bit less depressed.

This divergence in global housing market trends is welcome support for the theory of “decoupling”, the idea that the fates of the world's economies are less tied to America than they once were. It is not just emerging markets that are following a different path. In Australia and Sweden, where house prices are still rising rapidly, central banks raised their benchmark interest rates even after the Federal Reserve started to cut rates in America. But in much of the rich world, house prices have moved in tandem over the past decade. Now that America's housing market is so poorly, the fear of infection elsewhere is spreading like a bad case of the flu.