Epidemiology of an outbreak of infectious syphilis in Manitoba

An outbreak of 82 cases of infectious syphilis (primary, secondary, and early latent) which occurred in 1984 in the province of Manitoba was analyzed by age, sex, geographic distribution, and stage of disease. In the preceding four years, from 1980-1983, there were 19, 24, 13, and 32 cases, respectively, of infectious syphilis, of which 89% involved males. Compared with 1983, the overall crude incidence rate in 1984 increased by 259%, from 2.9 to 7.5/100,000 population, with a peak incidence in the 25- to 29-year age group of 25.8/100,000 population. This increase was predominantly due to a striking increase in incidence in females which rose 6.3-fold, from 0.4 to 2.5/100,000 females, compared with a 2.3-fold increase in males. This increase was accompanied by a decline in the male-to-female ratio, from 15.0 to 4.9. Of the 68 males, 45 named women as their sexual contacts. Females were 2.4 times more likely to present with early latent disease, whereas males were 7.0 times more likely to present with primary disease (p less than 0.01). There was clustering in suburban locations with regard to clinical presentation (60% primary disease) and overall incidence (46% of all cases). These data suggest the occurrence of a major change in the epidemiology of syphilis in the province of Manitoba, with a shift from homosexual to heterosexual transmission.