Blood Cultures: A Primer. Highland Hospital Blood Culture Isolates, 1/06-6/06

Transcription

1 Blood Cultures & Line Infections Infectious Diseases, Highland Hospital Blood Cultures: A Primer Definition o A bottle is not a culture Technique o Careful prep (CHG preferred) o ml blood o Culture media Areobic, Anaerobic, Fungal Timing Before the rigor Before the antibiotics Repeat after 30 minutes Number: o A single blood culture is dangerous o Two cultures is customary o Greater than 3 cultures adds little o Enough is enough Where o Central and Peripheral Highland Hospital Blood Culture Isolates, 1/06-6/06

2 Page 2 of 6 Contaminant or true positive? ~2-4% of cultures are false positives Leading contaminant cadidates: o coagulase negative Staphylococcus o Alpha-hemolytic streptococci o Diphtheroids Corynebacterium spp., Propionibacterium acnes o Bacillus spp. o Clostridium perfringens, anaerobes When is a contaminant not a contaminant? Repeated cultures positive for the same organism Cultures positive within 24 hours Foreign body in place Other culture systems Lysis centrifugation (AKA Isolators) o 10 ml of blood with detergent lysis of cells o Centrifuged for 10 fold concentration o Quantitative methods can be used if processed promptly o Specialized media can be inoculated Mycobacterial cultures Some fungi (Histoplasma, Aspergillus) Candida likes the regular bottles

3 Line Infections Types of lines Diagnosis Do we have to take the line out? Treatment Organism specific recommendations Page 3 of 6 Types of lines Nontunneled o Peripheral IV o Triple lumen central catheter (TLC) o Pulmonary artery catheter with Introducer o Peripherally-Inserted Central Catheter (PICC) Tunneled o Long term CVC (Hickman, Groshong, etc.) o Totally implanted device (Mediport) o Dialysis catheters Types of Infections Exit site infection Tunnel and Pocket infections Luminal infection Complicated infection o Endocarditis, septic phlebitis, osteomyelitis and other metastatic infections Gram stain of site Acridine orange stains of blood Cultures of the device Diagnosis o Quantitative: sonicate the segment, do several cultures to count organisms total ( 100 is significant) o Semiquantitative: roll the catheter on a plate. ( 15 colonies) o Qualitative: drop it in broth. Sensitive but minimal specificity Organism Load Determination From each port and from the periphery Lysis centrifugation cultures for quantitative cultures o Requires prompt processing o Ratio of central to peripheral of >5:1

4 Qualitative: positive central, negative peripheral Time-to-positive in standard cultures o More organisms go positive earlier o Difference of over 2 hours is sensitive and specific Do we HAVE to take the line out? Page 4 of 6 Maybe you can keep it if... o Clinically stable o Hard to replace catheter (tunneled) o Wimpy bug o Catheter is still needed Catheter should not be salvaged if... o Bad bug that causes metastatic complications (Candida kills.) o Clinically unstable (Shock, Organ system failure) o Complicated infection Endocarditis, septic thrombophlebitis, etc. Bacteremia beyond 3 days o Recurrence (Same organism, failed once) Treatment Systemic antibiotics o Empiric antibiotics should cover Gram-positive organisms: Vancomycin o If severely ill or compromised, GNR coverage o Narrow based on organism and sensitivity Antibiotic Lock therapy o X serum concentration in lumen o Increases catheter salvage from 20% to 67%-83%. o Vancomycin, aminoglycoside, or quinolone Regular line o heparin 100 units/ml with vanco 2mg/ml gent 50mcg/ml tobra 25mcg/ml Dialysis catheter o Vanco 10mg/ml and heparin 2500 units/ml o gent 20 mcg/ml and heparin 5000 units/ml

5 Page 5 of 6 Duration of Treatment Catheter removed o Generally 5-7 days, 14 days for bad bugs (S. aureus, Candida) from last positive culture o Local signs: days Catheter salvage o Parenteral therapy for 2 weeks with lock therapy for two weeks (some mix and match) Complicated infections o Endocarditis/Endothelial 4-6 weeks o Osteomyeltiis 6-8 weeks Coagulase negative Staphylococcus o Less mortality (0.7%) o More over-treatment o Catheter salvage reasonable (one try) o Treat with vancomycin (sometimes this can be narrowed.) o Adding Gentamicin or Rifampin doesnʼt seem to help Staphylococcus aureus Attributable mortality 8.2% Metastatic infections more likely Do Transesophageal Echo (TEE) if feasible o 16/69 (23%) had endocarditis If it isnʼt ORSA, donʼt use vancomycin since beta-lactams are more acitive Candida Line Infections Do not keep the line: mortality is increased Be aware of metastatic complications o Hepatosplenic candidiasis o Retinal lesions Treat with liposomal amphotericin B (1-3 mg/kg) or fluconazole 400mg/day or caspofungin 50mg daily. Treat for at least 2 weeks even if only one bottle is positive.

6 Page 6 of 6 Summary Get the cultures, and donʼt be thrown off by contaminants (or ignore Bad Bugs, even in low numbers) Use time to positive to prove infection, all lumens. In general, pull simple lines. Salvage gets at most one try in uncomplicated infections. Treat for 7 days for line out and uncomplicated, 28+ for complicated infections If possible, use antibiotic lock therapy to help salvage the lines. Guidelines at or