Suppose 100 women who reside in a neighborhood with above-median numbers of sexual partners among men are followed for an average of 5 years. What is the probability that exactly 20 of the women will develop HIV? 

Infectious Disease

Concurrent sexual partnerships are widely believed to be one of the main drivers of the HIV epidemic in sub-Saharan Africa. F. Tanser and colleagues followed 7284 initially HIV-negative women (‰¥15 years of age) residing in KwaZulu-Natal, South Africa, for an average of 5 years to evaluate relationships of the patterns of sexual activity with incidence of HIV [5]. Investigators surveyed men residing in the neighborhoods of the female study participants to determine patterns of sexual activity within each neighborhood. The table below shows the incidence of HIV acquisition according to whether a study participant resided in a neighborhood that was above vs. below the median in terms of the typical number of lifetime sexual partners among men in her neighborhood. 

Table 7.11 Relationship between HIV incidence rate and lifetime number of sexual partners in KwaZulu-Natal, South Africa

 

*Incidence of HIV acquisition (i.e., number of new cases).

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Lifetime sexual partners <6.2 partners (.e., below the median) 26.2 partners (.e., above the median) Person-years HIV cases" 9735.66 305 9539.92 388