Objectives: Aetiological diagnosis of bacteremia or fungemia by aerobic and anaerobic cultivation of the blood, with identification and susceptibility test of the isolated organism(s). Blood culture should be made for cases with suspected septicemia, endocarditis, and bacteremia secondary to localized infections (pneumonia, intra-abdominal abscesses, pyelonephritis, epiglottitis, meningitis). In this case the blood culture may provide an aetiological diagnosis of the localized infection.

The number of blood cultures: The number of blood cultures necessary for detecting bacteremia depends theoretically on the volume of blood inoculated, the time of collection, the type of infection and infecting organism, the age of the patient, and if the patient has received antibiotics prior to the culturing. The numbers of bacteria are generally higher in the acute, initial stage than at a later stage of the disease, and small children usually have higher numbers of bacteria in the blood than adults. The number is also higher when the fever rises than when it is falling. For patients expected to seed bacteria intermittently into the blood, 80% of these are detected with the first culture and 99% within three cultures. More than three cultures are therefore not necessary, unless the patient has received antibiotics. In this case, a new series of blood cultures may be indicated, after the antibiotic treatment has been stopped.

Collection time: Before the start of antibiotic therapy. If time permits, it is generally recommended that the first two sets of blood cultures be taken one hour apart and the third set after another 3-6 hours. If this is not possible due to the seriousness of the patient's illness, two sets of blood cultures should be drawn from two different sites before the antibiotic is administered.

Equipment: Request form, labels, blood culture bottles for aerobic and anaerobic cultivation, antiseptic solution (Appendix 5), cotton wool sponges, needles, syringes and tourniquet.

Procedure: 1. Fill in request form, identify the patient and explain what will happen.

2. Collect and assemble the equipment. Remove the protective cap from the culture bottles, if present.

3. Apply tourniquet and select an appropriate vein for the collection, usually the antecubital vein.

4. Disinfect the skin: apply the antiseptic solution to a cotton wool sponge and rub a 5 cm square area around the selected site for one minute. Leave the antiseptic to dry and discard the sponge. Make a new sponge and cleanse the site again, beginning at the centre and scrubbing in a circular motion outwards. Let it dry.

5. If necessary, palpate the site before the venepuncture. Disinfect the finger with the same procedure as described for the skin of the patient. Do not touch the prepared site with fingers that are not disinfected.

6. Disinfect the diaphragm of the blood culture bottles as described for the skin (not needed if there is a protective cap).

7. Insert the needle of the syringe into the vein and draw the volume needed for the culture.

8. Remove the tourniquet and withdraw the needle from the vein.

9. Immediately apply pressure to the puncture site with a clean cotton sponge.

10. Inoculate the culture bottles carefully, adding the correct amount of blood. Be careful that no air is injected.

11. Put a label on the bottle, indicating the patient's identification, ward number and time of collection, so as not to cover the area occupied by the medium.

Safety precautions: Do not puncture the same site twice as this may cause infection. Blood from a patient is potentially infected (hepatitis, AIDS) and when injecting it into the culture bottles be careful not to prick your fingers. Needles should not be recapped, but discarded in a safety container.

Storage: According to the manufacturer's instructions. Do not store inoculated bottles in the refrigerator.

Transportation: Bring the blood culture bottles to the laboratory immediately, and place the culture bottles immediately in the incubator.

Reporting: In case of positive culture, the result should be conveyed immediately to the treating physician or doctor on duty. Negative results are only reported after 7 days of incubation. If slow growing organisms are suspected - Brucella spp., Francisella tularensis - it should be clearly indicated on the requisition form, and the culture bottles should be further incubated for another 1 to 2 weeks before being reported out as negative.

Comments: When bacteremia is detected, the apparent primary infection focus (bone, joint, lung, kidney, intravenous line, etc.) should be verified by culture of specimens relevant to the situation. This is important for the duration of the antimicrobial treatment. Five to 30% of positive blood culture represents contamination with skin bacteria. Both gram-positive and gram-negative bacteria are found on the skin of healthy persons, but normally the gram-negatives are found in low numbers. In hospital patients and in patients receiving antibiotics the gram-negatives increase considerably in numbers. Though many of these contaminants can be recognized on the basis of their identity, others are very difficult to recognize. Therefore, to keep the number of contaminants low, proper skin disinfection is extremely important before doing a blood culture.