many risks factors are associated to the incidence of HIV

Women most commonly seek care from a gynecologist for the condition of vaginitis.

Do you really need four references for one piece of data?  If everybody is saying the same thing, it is often a generally accepted fact that does not need a reference at all.  Otherwise, just pick one reference, probably the oldest one.  You are giving a statistic, so you usually do need some sort of reference to show where the data comes from.  Either the data has been collected over & over or everyone is refering to the original data.