A chemical, which is believed to be a preservative, has been found in the coffee maker at Yale University's School of Medicine. The institution admitted that this could have caused four people to become sick last week.

It was previously reported that about three people got ill at Yale's School of Medicine. The victims were said to have felt lightheaded and dizzy. Officials investigated whether the coffee maker is to blame as each person drank from the source in Sterling Hall of Medicine.

The victims were rushed to the Yale New Haven Hospital and were released immediately. Officials of the city emergency management said that the state Department of Energy and Environmental Protection (DEEP) also conducted an examination on the coffee maker and cups and also took air as well as other material samples from the scene of the incident to help determine what caused the illness.

Now, the Associated Press, via U.S. News, reported that laboratory chemical sodium azide was detected to be present in the coffee machine. It is typically used in laboratories as preservatives.

Symptoms of exposure to sodium azide include headaches, nausea, vomiting, rapid breathing and heart rate. These are the same symptoms that the victims experienced last week.

University spokesperson Karen Peart said that the chemical was detected by independent lab tests on the single-service pod-style coffee machine. This has cleared the water source and the surrounding area from suspicion. However, it is still unclear on how the chemical came to be in the machine.

According to the Hartford Courant, Yale Police Department is still continuing with the investigation. They are working with local, state and federal law enforcement on the case.

DEEP previously announced that it was unable to detect anything that may have been the cause of the illness from the coffee maker. The department also recommended that Yale University call in an industrial hygienist to conduct further testing.