The largest outbreak of pneumonic plague in the U.S. since 1924 that sickened four people in Colorado in 2014 all started with a sick pit bull, according to a report from the Centers for Disease Control and Prevention.
The following are five things to know about this plague outbreak.
1. The first patient in this outbreak was hospitalized in July 2014 with pneumonia. An initial sample from the patient was misidentified as Pseudomonas luteola by an automated system in the hospital's laboratory. However, it was later properly identified as Yersinia pestis, the bacterium that causes plague. He was treated with broad spectrum antibiotics, including levofloxacin and streptomycin, and was discharged after being hospitalized for 23 days.
2. An investigation showed that the man had a pit bull that had fallen ill with various symptoms and was later euthanized because of the illness. After the man was diagnosed with the plague, tissue from the dog's liver and lungs was tested and was found to have the plague.
3. After the dog was diagnosed, investigators found that three additional people who had close contact with either the dog (two employees from the vet clinic where the dog was put down) or the first patient also developed the plague. All were successfully treated with antibiotics.
4. According to the CDC, this outbreak is notable because the bacterium from the first patient was misidentified, which slowed recognition that it was the plague. "Delayed recognition because of inaccurate laboratory test results and atypical clinical presentations can lead to high numbers of potential exposures to healthcare workers, laboratory workers and other close contacts," the report states.
It is also notable because of the possible human-to-human transmission of the plague. The fourth patient may have gotten the plague from the first patient — an event that hadn't occurred in the U.S. since 1924.
5. A median of eight cases of human plague are reported each year in the U.S., according to the CDC. The 2014 outbreak was a pneumonic plague outbreak, which is fatal more than 93 percent of the time if left untreated. Advancements in antimicrobial therapy have reduced the overall plague morality rate from 60 percent to about 16 percent.