Public health officials say rural counties across the Midwest and West are becoming the new battleground. While syphilis is still concentrated in cities such as San Francisco, Atlanta and Las Vegas, its continued spread into places like Missouri, Iowa, Kansas and Oklahoma creates a new set of challenges. Compared with urban hubs, rural populations tend to have less access to public health resources, less experience with syphilis and less willingness to address it because of socially conservative views toward homosexuality and nonmarital sex.

In Missouri, the total number of syphilis patients has more than quadrupled since 2012 — jumping from 425 to 1,896 cases last year — according to a Kaiser Health News analysis of new state health data. Almost half of those are outside the major population centers and typical STD hot spots of Kansas City, St. Louis and its adjacent county. Syphilis cases surged at least eightfold during that period in the rest of the state.