It warns, however, that the "window of opportunity" to prevent the spread of drug resistant strains will be missed if urgent action is not taken to persuade more health authorities and doctors to use its recommended treatment strategy, which still reaches only 1 in 5 patients with tuberculosis worldwide.

Drug resistance is significant only in countries without good control programmes

The warning comes in a global report released this week on World Tuberculosis Day at a ministerial summit in Amsterdam. It shows a disturbingly high prevalence of drug resistant strains of Mycobacterium tuberculosis in parts of eastern Europe and Asia.

By contrast, countries that have used the recommended treatment strategy tend to have very low rates of resistance. "We only see significant drug resistance in countries without good control programmes," said Dr Marcos Espinal, an epidemiologist and head of the report's team of authors.

The WHO has been arguing for directly observed treatment, short course ("DOTS") for years on the basis of small scale studies that show it helps to prevent the emergence of resistance.

But this report is the first that allows it to show a clear inverse relation between the numbers of patients receiving DOTS and the prevalence of resistant strains in a widespread sample of populations. "This conclusion is a 'no brainer' to those of us who have been involved in DOTS, but now we have the evidence," said a WHO spokesman.

The new report has data from 58 countries and other settings (such as provinces of China) and enough data to detect trends in 28. Its authors warn, however, that the picture is still incomplete. The scale of drug resistance is not fully known in the five countries with the highest incidence of tuberculosis worldwide: India, China, Indonesia, Bangladesh, and Pakistan.

As before, a high rate of resistance to one or more drugs was found in new tuberculosis cases in Estonia, with 37% of all strains resistant to any drug and 14% multidrug resistant. The prevalence of resistance in Estonia had grown substantially since the last survey, both in new cases and previously treated cases.

Other countries and settings with worrying rates of drug resistance included Latvia; two Russian "oblasts" (territories); Iran; the Henan and Zhejiang provinces of China; and Tamil Nadu state in India. Germany and Denmark have both seen increases in drug resistance, but the scale of the problem is small.

In the parts of eastern Europe where rates of resistance are high, a tradition of treating patients for lengthy periods in hospital has encouraged resistant strains to flourish.

Anti-tuberculosis Drug Resistance in the World is available from the Publications Department, World Health Organisation 1211 Geneva 27, Switzerland.