Blood Culture - Infectious Diseases

Infectious Diseases

Blood Culture

·        When to take them: 

o   It takes 30 – 60 minutes for temperature to rise after introduction of bugs into the blood, but endothelial cells of the vascular system (spleen, kuppfler cells, etc) phagocytose cells in minutes 

o   So when the temperature spikes, bugs may well be gone. So do random cultures in the hope of getting a hit

·        Definitions:

o   Bacteraemia: no host response.  Happens all the time (eg after cleaning teeth) 

o   Septicaemia: sustained bacteria in the blood stream – on going delivery of bugs into the blood stream from a replicating focus (don‟t multiply in blood). Leads to host response and disseminated loci of infection 

o   Pyemia (older term): Spread of organisms via infected thrombi

·        Infections associated with bacteraemia: 

o   Community acquired pneumonia (treat strep pneumonia with penicillin, except in children where > 30% resistance so use cephalosporin)

o   Meningitis with petechial rash (treat meningitidis with penicillin)

o   Osteomyelitis (treat S Aureus with flucloxacillin or vancomycin if MRSA)

o   Leukaemia with infected Hickman line (Coag –ive staph, eg epidermidis, treat with vancomycin)

o   Pyelonephritis (treat E coli with Gentamycin)

o   Cellulitis (treat Strep pyogenes with Penicillin)

o   Perforated appendicitis (treat B Fragilis with Metronidazole)

o   Infective endocarditis (treat viridians Strep, eg S sanguis, with penicillin + maybe gentamycin)

o   Epiglotitis (treat HIB with cephalosporin)

o   Premature baby with respiratory distress syndrome (treat Lancefield group B strep with penicillin)

·        Procedure for blood culture:

o   Ensure everything sterile – contamination makes interpretation very difficult

o   5 – 10 mls of blood in two bottles, one general purpose and the other anaerobic

o   For kids, use single 3 ml paediatric bottle

o   Choose vein (usually ante-cubital fossa)

o   Swab with betadine and wait 3 – 4 minutes to dry

o   Draw blood and inject into bottles

o   If already on antibiotics, notify lab

·        Indications for blood cultures:

o   Infection of any degree of severity – especially if firm clinical diagnosis not possible

o   Absence of fever doesn‟t rule out infection, so is not a contra-indication (eg confusion, feeling off)

o   Specific indications:

§  Acute generalised infection: fever, rigors, sweating, shock

§  Febrile illness + congenital or acquired heart disease where infective endocarditis suspected

§  Diseases with a bacteraemic phase (pneumonia, meningitis, acute pyelonephritis, etc)

§  Shock (especially post-operative following abdominal surgery)

§  Intercurrent illness in patients with compromised immunity 

o   Usually unnecessary to do more than 2 sets at the time bacteraemia is suspected, 20 minutes apart. If infective endocarditis, take 3 sets over 24 hours

·        Bugs isolated in Wgtn Hospital:

o   Four most common G+ive: Staph aureus, Staph coag –ive (from lines), strep pneumonia, enterococcus faecalis

o   Four most common G-ive: E. Coli, Klebsiella, Other Coliforms, Pseudomonas aeruginosa 

o   Most common is staph epidermidis (ie staph coag –ive): It‟s a common contaminant, but also the most common pathogen in catheter related infections, neonates and neutropenic patients. ­Resistance to Flucloxacillin ® ­use of vancomycin (expensive, side effects, etc)