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Eleven cases of human plague were reported in 6 states from April through August—a substantial increase compared with the annual number of US cases reported in recent years.
Public health experts who investigated the cases in Arizona, California, Colorado, Georgia, New Mexico, and Oregon said reasons for this year’s increase aren’t clear. From 2002 to 2012, the annual number of plague cases ranged from 1 to 17, with a median of 3 cases per year. In the current outbreak, 9 of the 11 patients are male with a median age of 52 years. Three patients aged 16, 52, and 79 years have died (Kwit N et al.MMMR Morb Mortal Wkly Rep. 2015;64:918-919).
Plague is a rare zoonosis caused by the bacterium Yersinia pestis, which is carried by fleas that infect wild rodents in rural and semirural areas in the western United States. Three of the current cases have been traced to or near Yosemite National Park in California. People contract plague through the bite of infected fleas, from direct contact with infected body fluids or tissues, or by breathing respiratory droplets from ill people or animals, including pet dogs and cats.
Bubonic is the most common form of plague, accounting for 80% to 85% of cases. Illness results from the bite of an infected flea. One or more lymph nodes swell in these patients, causing a painful “bubo.” Septicemic plague occurs in 10% of plague cases, results from a flea bite or direct contact with infectious fluids, and has no localizing signs. Primary pneumonic plague accounts for 3% of plague cases as a result of inhaling infective droplets and develops into a fulminant primary pneumonia.
With prompt treatment using antimicrobials, such as aminoglycosides, fluoroquinolones, or doxycycline, mortality from plague is approximately 16%. Recommendations for diagnostic testing and antibiotic treatment, and information on plague prevention, are available on CDC websites (http://1.usa.gov/1QthBJI; http://1.usa.gov/1Q724OQ).