Background and objectives: The basic reproductive ratio, RO, is a useful measure to compare the potential for spread of sexually transmitted diseases (STDs) between populations. But RO is a population risk measure; and individual risk index is needed.
Study design: An individual, STD-specific potential risk index was developed based on the basic reproductive ratio formula. The index was estimated for 10,643 subjects aged 18 to 60 years taking part in surveys of sexual behavior conducted in 1987 and 1992, using human immunodeficiency virus (HIV) and chlamydial infections as examples.
Results: Of the total population, 2.8% were at potential risk for HIV infection, and 5.2% for chlamydial infection. The two groups overlapped only partially. There where more than 15 times as many at potential risk among single subjects as among married/cohabiting subjects for both infections.
Conclusions: The risk index developed measures STD-specific potential risk. It can be used to estimate the size of risk groups in populations, and the association between risk and sociodemographic and behavioral variables. Further research is needed to include the effects of partner mixing in the index.