Much of reported sexually transmissible disease is located in lower income areas of a community, as shown in this geomap of reported Syphilis in Portsmouth. The disease is almost completely confined to the lowest income area of the city. Why do you think this might be?
Whereas Gonorrhea is a measure of bacterial disease, usually heterosexual, syphilis requires an open sore, anywhere on the skin or the mucosa. If the recipient has any lesions on the body, that individual can be infected but the disease is less obvious than GC, because the initial sore (chancre) is painless and disappears within 7 days, followed by a skin rash, and later by a tertiary disease which spreads through the blood vessels.
Syphilis is frequently a homosexually spread disease but can be spread through exchange of blood and during use of injectable drugs. This provides another measure of adverse behavior in the community, which can be affected by community action.
More importantly recent increases of syphilis have been associated with increased transmission of HIV.
(This map was created when I was health director in Portsmouth, VA, in the late 1960s in response to the CDC grant to look at sociodemographic distribution of disease, one of tfe first such grants from the CDC, pub:proceedings of the 1972 Annual Communicable Disease Conference)