PATIENT CHARACTERISTICS: Age: 2 and over Performance status: Not moribund or comatose for any reason with little hope of recovery Life expectancy: At least 48 hours Hematopoietic: See Disease Characteristics Hepatic: No hepatic stupor or coma Renal: Adults: No renal failure requiring hemodialysis or peritoneal dialysis OR Creatinine no greater than 2.25 mg/dL OR Creatinine clearance at least 40 mL/min Children: No renal impairment (i.e., creatinine greater than upper limit of normal) Pulmonary: No lung infiltrate Other: No known allergy to piperacillin, tazobactam, or vancomycin No history of immediate or accelerated reaction to beta-lactam antibiotics No prior inclusion in this study No catheter related infection No known HIV infection Not pregnant or nursing