The Daily Sentinel reports officials say the latest exposure may have been contracted from a deer fly or tick bite while the woman was in the Ruby-Horsethief section of the Colorado River.
Earlier this month, Mesa County officials confirmed that a woman contracted the disease likely during a rafting trip on the river.
Two people from out of state were also diagnosed with the infection after spending time on the river during the same time period the two Mesa County residents were infected.
Officials say there's been 27 cases in Colorado this year, compared to 16 cases in all of 2014.
Tularemia is carried by several animals, including rabbits and squirrels.