A rare case of pneumonic plague has been diagnosed in a patient who is hospitalized in Colorado. Health officials say it is the first confirmed case in the state since 2004.

Plague was also confirmed in the family dog, after the dog died unexpectedly.

The plague -- the illness that killed millions of people across Europe in the Middle Ages -- is a bacterial infection spread by fleas from rodents. Pneumonic plague is caused by the same bacteria as bubonic plague but it attacks the lungs. It can be treated with antibiotics, but sometimes is still deadly.

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State health officials did not say whether the infected patient is a man or woman, but confirmed that the person has been hospitalized. Officials believe the patient and dog may have been exposed in eastern Adams County, northeast of Denver.

Officials are looking for people who may have had contact with the patient so they can be treated with antibiotics.