Patterns of sexual mixing: mechanisms for or limits to the spread of STIs?

Prevalence and incidence of sexually transmitted infections (STI) vary across subpopulations defined by age and race ethnicity.1–5 Some ethnic groups—for example, African and Caribbean blacks6 in the United Kingdom and African-Americans1 in the United States, have higher rates of STI including human immunodeficiency virus (HIV) infections, while other ethnic groups—for example, Asians in both the United Kingdom and the United States, have lower incidences of STI and AIDS. The reported incidence and prevalence rates often exaggerate the race ethnicity differentials in STI. In the United States the majority of the population seek STI related health care through private healthcare providers,7 while the number of STI cases reported from public sources exceeds that reported by private providers by a wide margin.1 To the extent that minority race ethnicity subpopulations seek STI related health care through public facilities, STI cases among these groups are overreported in the national data. Surveillance systems tend to collect data on either race ethnicity or socioeconomic status; thus, often it is impossible to analyse the effects of both sets of variables on STI incidence. Moreover, the multicollinearity between race ethnicity and socioeconomic status makes it difficult to delineate the independent contribution of ethnicity to differentials in STI rates even in those rare …