By Denise Roland 

GlaxoSmithKline PLC said it expected to reopen its manufacturing plant in Zebulon, N.C., in the next 72 hours, after concluding that Legionnaires' bacteria found in two external cooling towers posed no risk to its products.

The pharmaceutical company shut down the plant Tuesday after discovering the bacteria, which causes a potentially fatal form of pneumonia, during a routine test. All staff on the site were sent home and told to stay away while the company inspected the towers.

"Given the location and level of bacteria found, this situation posed no risk to the products manufactured inside the building," a spokeswoman said. "We anticipate resuming production in the next 72 hours after cleaning, disinfecting, and returning the plant back to normal operating conditions."

The cooling towers are separate structures from the buildings in which staff work and products are made. Inhaled products including the company's best-selling inhaler, Advair, are made at Glaxo's Zebulon site.

Legionnaires' is contracted by inhaling water vapor contaminated by the bacteria and isn't contagious, according to the U.S. Centers for Disease Control and Prevention. The illness is fatal in 15%-to-20% of cases, according to the World Health Organization.

Write to Denise Roland at Denise.Roland@wsj.com

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