BEIJING (Kyodo) -- Two people from northern China's Inner Mongolia were diagnosed in Beijing this week with pneumonic plague, a highly infectious disease that is fatal if left untreated, state-run media reported Thursday.
People who had close contact with the two have been quarantined for medical observation, with none having reported any abnormal symptoms, Xinhua News Agency reported.
One of the patients is in stable condition, while the other is critically ill but without further deterioration, the report said, quoting the Beijing Municipal Health Commission. It gave no information of their ages or sex.
The commission confirmed Tuesday that the two were transported by ambulance from the autonomous region to a medical institution in Beijing's Chaoyang District where they were diagnosed with the severe lung infection, according to Xinhua.
Pneumonic plague is the most virulent form of plague, with a case-fatality rate of 30 to 100 percent, according to the World Health Organization. It can be transferred from person to person through infected droplets expelled by coughing or sneezing.
It is one of two main clinical forms of plague infections caused by the bacteria Yersinia pestis, usually found in small mammals and their fleas. Known as the Black Death in 14th-century Europe, the plague is infamous for killing tens of millions of people.