CORRECTED-UPDATE 1-No new brain-infection cases with Biogen drug

(Corrects Oct. 11 story to show date of Tysabri's return to market was July 2006, not last July) (Updates with details, analyst comment)

BOSTON, Oct 11 (Reuters) - Biogen Idec Inc (BIIB.O) and partner Elan Corp (ELN.I) said on Thursday that as of the end of September there have been no new reported cases of a potentially deadly brain infection in patients taking their multiple sclerosis drug Tysabri.

Cambridge, Massachusetts-based Biogen and Ireland-based Elan released the data ahead of a presentation at the Congress of the European Committee for Treatment and Research in Multiple Sclerosis in Prague.

The companies said about 17,000 patients are taking Tysabri in the United States and Europe. Of those, 1,000 are in clinical trials.

Tysabri was taken off the market in 2005 after being linked with three cases of progressive multifocal leukoencephalopathy, or PML. The U.S. Food and Drug Administration allowed the drug back in July 2006 because it is effective and patients asked for it to be returned.

Tysabri is available in the United States through a safety-monitoring program known as TOUCH. All prescribers, infusion sites and patients are required to enroll in the program, which is designed to monitor patients for any signs or symptoms of PML.

The longer time goes by with no new cases of PML, the more comfortable doctors are in prescribing it.

"The Tysabri safety and utilization update provided today gives us comfort with our Street-high 2007 Tysabri worldwide end user sales forecast of $357 million."