Armed with more than a decade’s worth of statistics, researchers are sounding a new alarm about growing rates of syphilis among gay and bisexual men.

The overall number of syphilis cases in the United States fell from 50,578 in 1990 to just 7,177 in 2003 perhaps because of a nationwide prevention campaign aimed at heterosexuals. Nevertheless, gay men have seen their rates rise significantly in this decade.

"The entire nation was caught unawares," said study lead author James Heffelfinger, M.D., a medical epidemiologist with the Centers for Disease Control and Prevention. "You’re concentrating on one population, but the next thing you know, you start seeing a large increase among another group."

It is still easy to cure syphilis, but it can cause serious medical problems, including death if untreated. In addition, officials worry that gay men will get syphilis and become more susceptible to HIV infection, although statistics have not made it clear if that is actually happening.

The study authors looked at syphilis rates from 1990 to 2003 and reported the changes during that time. The American Journal of Public Health released the findings online this week, and they will also appear in the June print edition.

Between 1990 and 2000, syphilis rates fell by a whopping 90 percent, from a rate of 20.3 cases per 100,000 people to 2.1 cases per 100,000. Among other factors, public health officials think the rates dropped because fewer people were selling sex to get crack cocaine as the decade went by.

However, the syphilis rate rose by 19 percent between 2000 and 2003.

During that period, the rates among women continued to slide — by 53 percent — while rates among men jumped by 62 percent. While syphilis statistics do not identify the gender of the sex partners of infected people, the study authors infer that a large number of those infected — 62 percent in 2003 — are gay or bisexual, in part, because so few women become infected.

The study does not look past 2003, but statistics suggest the trends continued through 2005, Heffelfinger said. There were 8,724 new cases of syphilis recorded in 2005.

Khalil Ghanem, M.D., assistant professor of medicine at Johns Hopkins University School of Medicine, said rates among gay men could be going up for several reasons, including illicit drug use and "safe-sex fatigue." In addition, he said, prevention messages might have been "drowned out" by talk about how medications are doing a great job of keeping AIDS patients alive.

"We’ve been seduced by these amazing drugs and we’ve fallen behind in our prevention efforts," Ghanem said. "We have to get back on track with prevention messages. That’s the only way we will curb this outbreak."

Source: Heffelfinger JD, et al. Trends in primary and secondary syphilis in the United States: The reemergence of syphilis among men who have sex with men. Am J Public Health 97(6), 2007.