China faces a "serious epidemic" of drug-resistant tuberculosis according to the first-ever nationwide estimate of the size of the problem there, said a US-published study on Wednesday.

"In 2007, one third of the patients with new cases of tuberculosis and one half of the patients with previously treated tuberculosis had drug-resistant disease," said the study in the New England Journal of Medicine.

Even more, the prevalence of multi-drug resistant (MDR) TB in new cases (5.7 percent) was nearly twice the global average, said the study.

Using World Health Organization figures as a basis for comparison, "China has the highest annual number of cases of MDR tuberculosis in the world -- a quarter of the cases worldwide," it added.

"China has a serious epidemic of drug-resistant tuberculosis."

The data came from a survey of more than 4,600 Chinese people who were recently diagnosed or treated for TB.

Patients for the study were treated at local TB clinics, not hospitals, and the survey was conducted by the National Tuberculosis Reference Laboratory (NTRL) of the Chinese Centers for Disease Control.

According to an accompanying editorial by Johns Hopkins University infectious disease specialist Richard Chaisson, the growth of drug-resistant TB presents an "enormous challenge."

Even more concerning was the finding that most of the 110,000 drug-resistant cases were in people newly diagnosed with the disease, suggesting that the virulent bacteria are being transmitted from person to person and not developing solely as a result of a person prematurely stopping treatment.

"MDR tuberculosis is linked to inadequate treatment in both the public health system and the hospital system, especially tuberculosis hospitals; however, primary transmission accounts for most cases," said the study.

Chaisson said the findings highlight the need for faster testing, and for new cases of TB to be tested for signs of drug resistance, not just recurrent forms.

In China, over one million new tuberculosis infections occur each year -- a large chunk of the estimated nine million new cases worldwide annually.

Known formally as Mycobacterium tuberculosis, TB spreads through the air when infected people cough up bacteria. TB kills about 1.5 million people worldwide each year.

Often it can be cured with antibiotics, though drug availability is limited in the developing world and sometimes patients do not follow the entire regimen of treatment, which can encourage the development of resistant strains.

The study was funded by the Chinese Ministry of Health.