nearly 200 people were placed under observation at the hospital in Shelekhov to which the laboratory technician was taken.

Quarantine has also been imposed in at least one of the city's maternity hospitals, according to Liudi Baikala.

The infection in the Irkutsk region is  most likely not the plague, but even if confirmed, there will be no spread of this disease,  a previous head of Rospotrebnadzor, Gennady Onishchenko, said on Friday.

Onishchenko told the state news agency TASS that the onset of cold weather would likely prevent transmission.

Pneumonic plague is one of three types of plagues that are caused by the bacterium Yersinia pestis. The other two types typically spread from contact with infected fleas, animals, or infected tissues. But the pneumonic plague, or lung-based plague, can transfer easily from person to person through respiratory particles.

A U.S. State Department spokesperson told CNN Sunday that it is aware of the possible death due to pneumonic plague in Russia.

 We are monitoring the situation closely with the CDC and our other interagency partners,  the spokesperson said.  Many details have not been confirmed. We encourage Russian authorities to share accurate information quickly and openly. 

Patients with pneumonic plague develop fever, headache, weakness and  a rapidly developing pneumonia with shortness of breath, chest pain, cough, and sometimes bloody or watery mucous,  according to the U.S. Centers for Disease Control and Prevention (CDC). The U.S. Department of Health and Human Services told CNN that the CDC is closely monitoring the situation in Russia, and that the  safety and security of U.S. citizens is our highest priority. 

The World Health Organization has noted that plague has a high fatality rate, but is also easily treated with antibiotics and the use of precautions to prevent infections.