Six Harvard University medical researchers who became sick in August after drinking coffee were poisoned, according to university officials.

In a memo released Friday, the school says the victims all drank from a coffee machine on Aug. 26 that later tested positive for sodium azide, a common preservative used in labs.

The memo, written by Daniel G. Ennis, executive dean for administration, and Richard M. Shea, associate dean for physical planning and facilities, does not say whether officials believe the poisoning was intentional.

"We are in the process of installing additional security cameras throughout our buildings, and we are strengthening the security systems that manage access to the laboratories during both normal business hours and off hours," the memo states.

The six reported symptoms ranging from dizziness to ear ringing, and one passed out. They were treated at Beth Israel Deaconess Medical Center and later released.

The researchers, which include staff and students, all work in the Harvard Medical School's pathology department in its new Boston research building. They were using mice to investigate how diseases interact with the immune system.

Harvard spokesman David Cameron said no student or employee has been disciplined. The Suffolk District Attorney's Office said it was not aware of the incident, and the Boston Police Department was not investigating.

According to the memo, the federal Occupational Safety and Health Administration as well as the Boston Public Health Commission are conducting an investigation.

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