Alexion, the hugely successful biopharmaceutical company based in Cheshire, disclosed to investors that last week's inspection by the Food and Drug Administration of its Rhode Island factory suggest the company still needs to find "the definitive root cause" of prior contamination in vials of Soliris.

Soliris, which costs more than $400,000 a year per patient, is manufactured in Smithfield. Alexion said that the inspection's conclusions should not interrupt the supply, and that manufacturing is continuing at the site.

The FDA also told Alexion that the company needs to do more frequent environmental monitoring and needs better training on how employees wear their gowns on the job.

"Addressing FDA observations and advancing quality initiatives has been a key priority for Alexion and the company has enhanced and expects to continually enhance its overall quality program," the filing said.

Alexion is receiving tens of millions in state subsidies through the First Five Program for adding jobs at its future headquarters in New Haven. The package includes a $6 million grant from the state, a subsidized $20 million loan that will be made into a gift if Alexion has 650 workers in Connecticut by 2017 and tax credits that could be worth as much as $25 million.