SIOUX FALLS - There were 11 cases of syphilis last year in South Dakota and 13 in 2006.

Two cases a year are normal.

Most of those diagnosed with the venereal disease were from the Sioux Falls area.

A state Health Department official says the infections were centered in a cluster of people, but no new infections have turned up recently.

Tracking focused on transients, but efforts to stem the disease were complicated by drug use.

Methamphetamine increases the sex drive, and some of those with syphilis could not remember their sexual encounters.

Syphilis used to be more widespread in South Dakota.

More than 500 cases were reported in 1947.