WARREN, Mich. (Michigan News Source) — General Motors has temporarily closed its Cole Engineering Center after tests found Legionella in the building’s water system, the bacteria behind Legionnaires’ disease, a severe pneumonia that spreads through contaminated droplets.

Nearly 11,000 engineers and designers have been working remotely since Sept. 10, when two employees fell ill. Both have since recovered, but GM says the building will stay closed at least through this week while third-party experts review results and design a cleanup plan.

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“We will develop and implement a detailed remediation plan for all affected systems before reopening,” GM spokeswoman Tara Kuhnen said in a Sept. 24 statement, noting the company intends to clear all affected systems before staff return.

Legionella is commonly found in plumbing and cooling systems, making large facilities like the Warren engineering hub especially vulnerable.