CHAPEL HILL - Interstate 95, which snakes through the eastern third of North Carolina, not only promotes rapid movement of vehicles between the North and South, it also facilitates the spread of syphilis, according to a new study.
Drug trafficking appears to contribute heavily to the contagion.
The study, conducted at the University of North Carolina at Chapel Hill schools of public health and medicine and the University of Pittsburgh, showed 10-year syphilis rates in counties bordering the interstate greatly exceeded rates in counties in the state not bordering the highway. Per 100,00 people, about 38 cases occurred in counties near I-95, while 16 cases were identified in counties elsewhere.
No such research has been done in the United States before, although comparable studies have taken place in Africa, India and Southeast Asia, scientists say.
Authors of a report on the findings appearing in the March issue of the American Journal of Public Health are Drs. Robert L. Cook and Barbara H. Hanusa of UP's Center for Research on Health Care and Drs. Rachel A. Royce and James C. Thomas of UNC-CH's epidemiology department. Cook was former Robert Wood Johnson Clinical Scholar at UNC-CH's medical school.
"Syphilis rates were stable until 1989, when rates increased sharply in I-95 counties but remained stable in non-I-95 counties," the authors wrote. "Drug activity increased in I-95 counties one year before the rise in syphilis cases."
Over the decade studied --1985-94 -- the percentages of the population who were poor, non-white, female or young adult changed little, the researchers found. In contrast, drug arrests related to cocaine or heroin varied significantly.
"The pattern of arrest rates was remarkably similar to the pattern of syphilis rates, increasing dramatically in I-95 counties from 1987 to 1989, just prior to the increase in syphilis rates in these counties," the authors said.
Researchers analyzed data from the N.C. departments of transportation and of environment, health and natural resources and the State Bureau of Investigation. They also looked at syphilis rates near I-85, I-77, I-40 and I-26. Counties along I-95 were the only ones with syphilis rates above the state average and remained so after controlling for race, age, sex, income and larger cities.
They undertook the study to better understand highways' role in the U.S. syphilis epidemic that peaked in 1990. I-95 connects New York City and southern Florida, where infection rates were high.
A possible explanation for why the interstate boosted syphilis' spread was contact between truck drivers and local prostitutes, the authors said. In the 1960s, the diary of a prostitute infected with syphilis enabled public health workers to identify 168 long-distance truck drivers who had been exposed. Another more likely factor was cocaine distribution along I-95, which created a drug market that increased risky behaviors as people exchanged sex for drugs.
"This analysis suggests that counties along some interstate highways are particularly vulnerable to the spread of syphilis, especially if the highway connects areas of high disease prevalence," they wrote. "Counties along these highways may thus benefit from additional resources to fight epidemics in future outbreaks."
Note: Cook can be reached at 412-692-4841 or 4843, Royce at 919-966-7440 and Thomas at 919-966-7434.
Journal
American Journal of Public Health