B. Jonsson et al., THEORETICAL ASPECTS OF DETECTION OF BACTEREMIA AS A FUNCTION OF THE VOLUME OF BLOOD CULTURED, APMIS. Acta pathologica, microbiologica et immunologica Scandinavica, 101(8), 1993, pp. 595-601
Clinically significant bacteraemia in adults is characterized by low n
umbers of circulating bacteria. Assuming a Poisson or a binomial distr
ibution we have calculated the probability of detecting bacteria as a
function of the concentration in blood, estimated the concentration of
bacteria in blood from a given test result, and calculated the blood
volume required to detect bacterial growth with a probability of 95% a
t a given mean number of colony-forming units (cfu) per sample unit. T
hese theoretical assumptions have been used on an empirical population
of patients with proven bacteraemia. Results: 18% of Staphylococcus a
ureus bacteraemias and 29% of Escherichia coli bacteraemias have circu
lating bacteria with an estimated spread of less than 0.04 cfu/ml. Wit
h a 95% probability of detection of a bacteraemia, a concentration in
blood corresponding to 3 cfu/sampling unit is necessary. In our empiri
cal material, where 30 ml was cultured, the probability of detection o
f E. coli bacteraemias would have decreased by 11% if 20 ml had been c
ultured, and 27% if only 10 ml had been cultured. The corresponding fi
gures for S. aureus were 6% and 15%, respectively. For low grade E. co
li bacteraemias (<0.04 cfu/ml) the decrease would have been 33% and 67
%, respectively.