The Californian authorities said that a second tourist who visited Yosemite National Park has likely contracted the plague.
The unnamed individual, from the southern US state of Georgia, had vacationed in Yosemite, the Sierra National Forest and surrounding areas in California early this month.
"Warnings issued in California regarding plague were useful all the way across the country in Georgia," Karen Smith, the director and state health officer for the California Department of Public Health said on august 18.
"Those warnings helped the patient get the prompt medical attention necessary to recover from this illness."
The Centers for Disease Control and Prevention are carrying out tests to confirm the presumptive case. Plague is carried by squirrels, chipmunks and other wild rodents and their fleas.
On August 6, authorities announced that a girl from the Los Angeles area who visited the park in mid-July tested positive. She was treated and has since recovered.
The Crane Flat Campground where she stayed was subsequently closed for four days and fumigated. The Tuolumne Meadows Campground also was temporarily shut after several dead squirrels were found to be carrying the plague.
Authorities said that despite the presence of the plague in wild rodents at both campgrounds over the past two weeks, the risk to humans is low.
Yosemite National Park, located in northern California's Sierra Nevada mountains, is the third-most visited of America's national parks -- and one of the oldest.