TMP-STX resistance could have several possible explanations given the patient population examined; 1) As the majority of the patients had a history of intravenous drug usage, it is possible they had more abscesses in the past and had been treated with TMP-STX several times or 2) the majority of the patients had CD4 < 200 cells/mm3 and were most likely taking TMP-STX for prevention of pneumocystis pneumonia. Here, CD4 is linked to pneumocystosis.