Mirtazapine More Drug_warnings_recalls Question About Mirtazapine And White Blood Cells?

Question about mirtazapine and white blood cells? - mirtazapine more drug_warnings_recalls

I began taking mirtazapine 15 mg per day, a week before against fear. It says on the label, in rare cases "Sudden severe lack of white blood cells"

Is this true, and this increases the risk of contracting HIV through unprotected oral sex. I know that the risk is generally low but not zero.