There have been 11 cases of human plague in the U.S. since April,  according to a report released Tuesday by the Centers For Disease Control and Prevention (CDC). The number of cases reported since April 1 is higher than usual, CNN reported Tuesday, putting doctors across the nation on alert.  

"We don't want people to panic, but we do want people to be aware of the heightened risk," said Dr. Natalie Kwit, a veterinarian with the division of vector borne diseases at the CDC, CNN reported.

The report stated that out of the 11 cases of human plague reported since early April, three of them resulted in death. There were two cases in Arizona, one in California, four in Colorado, one in Georgia, two in New Mexico and one in Oregon. In the cases out of Georgia and California, the residents had been linked to exposure at or near Yosemite National Park, located in the southern Sierra Nevada Mountains of California, according to the CDC report.

Nine of the 11 plague patients were male, and the median age was 52 years old, the report stated. The three patients that died were 16, 52, and 79 years old.

GettyImages-456691988 The CDC published a report alerting doctors of an uptick in human plague cases since April. Photo: Getty Images

It is not clear why the number of cases this year so far is higher than normal, but the number does tend to fluctuate a little bit from year to year, according to Dr. Natalie Kwit, a veterinarian with the division of vector borne diseases at the CDC, CNN reported. From 2001 to 2012, the average number of human plague cases reported was seven, with less than one death caused by the illness per year, but in 2006, there were 17 cases reported.

The purpose of the report was to put the uptick of human plague cases on the radar for physicians who incur patients that have a fever or swollen lymph nodes and who might have travel and exposure history, said Kwit, according to CNN.

Plague is a rare but life-threatening disease. Patients are typically infected after being bitten by a flea who was infected with the disease by a rodent. Patients can be treated successfully with antibiotics if the disease is caught early enough; the death rate for people with plague who receive treatment is 16 percent compared to a death rate between 66 to 93 percent for those who are not treated.

The CDC report recommended that people who engage in outdoor activities in areas where the plague is prevalent, which includes rural and semi-rural areas of the western U.S., wear long pants when possible and use insect repellent on clothing and skin.