Executive Summary
Health officials note an uptick in cases of bubonic plague in the United States this year, with at least 12 reported human cases reported since April 1. The CDC notes that healthcare providers should consider plague in patients who have traveled to plague-endemic areas and exhibit fever, headache, chills, weakness, and one or more swollen or tender and painful lymph nodes, referred to as buboes. Officials note that the disease rarely passes from person to person, but that this is a concern with patients who have developed the pneumonic form of the disease.
• Health officials note that in recent years there has been an average of seven cases of human plague each year in the United States, and that most of these cases are the bubonic form of the illness.
• Four patients confirmed to have plague this year have died, including the most recent case, a Utah man in his 70s.
• Most cases of plague in the United States occur in two regions. The first includes northern New Mexico, northern Arizona, and southern Colorado, and the second includes California, southern Oregon, and far western Nevada.
• When plague is suspected, treatment with antibiotics should begin immediately.
Obtaining a thorough travel history, which is so important to picking up on signs of Ebola Virus Disease, is also key to identifying a case of bubonic plague, a disease that has been diagnosed in at least 12 people in six states since April 1, according to the CDC. The agency reports four patients have died from the illness.
“In recent decades, an average of seven human plague cases [have been] reported each year … and 80% of U.S. plague cases have been the bubonic form,” explains Natalie Kwit, DVM, MPH, an epidemic intelligence service officer at the CDC’s National Center for Emerging and Zoonotic Infectious Diseases at Fort Collins, CO. While Kwit is not sure why the number of cases has ticked up this year, she notes that the agency wants people to be aware of the heightened risk of plague in some Western states.
Kwit explains that most human cases in the United States occur in two regions. The first includes northern New Mexico, northern Arizona, and southern Colorado, and the second includes California, southern Oregon, and far western Nevada.
“Healthcare providers should consider plague in a patient that exhibits fever, headache, chills, weakness, and one or more swollen or tender and painful lymph nodes (called buboes) with a history of travel to plague-endemic areas,” Kwit says. “Other symptoms may include abdominal pain, nausea, or rapidly developing pneumonia with shortness of breath, cough, chest pain, and sometimes bloody or watery mucus/sputum.”
However, there is a danger that plague can be missed by providers if they are not thinking of it because the symptoms mimic other infections, particularly if there is no bubo, Kwit notes.
“It is important healthcare providers consider the diagnosis of plague in any patient with compatible symptoms, residence, or travel in the Western United States, and recent proximity to rodent habitats or contact with rodents or ill domestic animals,” she explains. “Providers should be aware of the possibility of plague and take a good travel/exposure history.”
Begin treatment immediately
If plague is suspected in a patient, samples of the patient’s blood, sputum, or lymph node aspirate need to be sent to a laboratory for testing, but treatment with antibiotics should commence immediately, according to Kwit. Preliminary lab results are typically available within two hours, although confirmatory results will usually take one to two days.
Left untreated, plague bacteria can invade the blood stream, multiply, and spread rapidly throughout the body, causing septicemic plague, which is often fatal, Kwit says.
“Untreated or septicemic plague can also progress into an infection of the lungs, causing pneumonic plague,” she says. “Although plague can spread from person to person, this is very rare,” Kwit advises. “A person who has pneumonia caused by plague may cough up droplets that contain plague bacteria, and [these] can cause pneumonic plague if [they are] breathed in by another nearby person with direct and close contact. This is the only way that plague can spread between people.”
Consequently, healthcare providers should consider isolating a suspected plague patient with respiratory involvement and implement respiratory droplet precautions, Kwit advises. Further, as the incubation period for pneumonic plague is typically two to four days, but can be as long as six days, antibiotics should be considered for people who have been in close contact with a person who has the pneumonic form of the disease within the previous seven days.
“Doxycycline, ciprofloxacin, and levofloxacin are the most effective antibiotics for preventing plague and should be taken for seven days,” Kwit says. “Close contacts should also measure their temperature twice a day for seven days and see a physician if fever develops.”
Kwit adds that people who have had some contact, but not close contact, with a person who has pneumonic plague within the previous seven days should be monitored for fever or cough and seek treatment if symptoms develop.
Consider climate, animal links
Scientists believe that plague bacteria circulate at low rates within populations of certain rodents, but other species become infected on occasion, causing an outbreak among animals, referred to as an epizootic, Kwit says.
“Humans are usually more at risk during or shortly after a plague epizootic,” she explains. “Studies have suggested that these outbreaks are more likely during cooler summers that follow wet winters and in areas with a variety of rodents living in high [density locations] and in diverse habitats.”
Typically, fleas become infected by feeding on rodents and other mammals that are infected with the plague bacteria, and then the fleas transmit the disease to people and other mammals, Kwit says.
“Although cases can occur at any time of the year, most cases in the United States occur from late spring to early fall,” she adds.
The most recent death attributed to plague occurred in Utah in August, according to health officials. They believe that the victim, a man in his 70s, probably contracted the disease from a flea or contact with a dead animal. Wildlife experts note that an outbreak of bubonic plague killed 60 to 90 prairie dogs in an eastern Utah colony not long before the man’s death. State health officials note that the last reported human case of plague in Utah was in 2009, but this was the first death attributed to the disease in the state in more than three decades.
Some of the other cases of plague reported this year have involved people who recently visited Yosemite National Park in California.
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Natalie Kwit, DVM, MPH, Epidemic Intelligence Service Officer, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Fort Collins, CO. E-mail: [email protected].
