The infection rate of syphilis in married couples has been reported by a few investigators during the 1940s. However, studies on recent trends of that particular aspect of syphilis in married couples have not yet been done.

We therefore studied the infectivity of T. pallidum and recent trends of conjugal syphilis by observing the spouses of patients with untreated syphilis.

Couples married for more than 1 year who visited Yonsei Medical Center from 1983 to 1990 for syphilis were entered into this study. We observed the infection rate among spouses of 224 index patients (defined as, between husband and wife, the one who was the first to be diagnosed to have syphilis) who were not treated for syphilis. Syphilis was diagnosed on the basis of physical examination, history of extramarital sexual contacts, and the results of VDRL, TPHA, FTA-ABS, and 19S(IgM)-FTA tests.

Fifty-six wives(48%) of 117 male index patients and 50 husbands (47%) of 107 female index patients had been infected at the time of examination. Among the 224 couples, 106(47%) were both infected and in 118(53%), only either husbands(27%) or wives(26%) were infected. Two spouses(50%) of the 4 first incident patients with primary syphilis, 9(53%) of 17 with secondary syphilis and 23(72%) of 32 with early latent syphilis were infected at the time of examination.

From our results showing the low infection rates among married couples, even in early syphilis when the infectivity is high, it can be deduced that T. pallidum has only a low infectivity.