Changes in blood culture methodology have an impact on time trends of bacteraemia: a 26-year regional study

The incidence of bacteraemia has increased considerably during the last decades. This may be related to population ageing, increased use of invasive procedures, and increased ascertainment of bacteraemia. Generalized additive and generalized linear models were used to analyse the impact of four successive improvements in blood culture methodology on the recovery of prevalent blood culture isolates while simultaneously controlling for underlying time trend and seasonal variation. Between 1981 and 2006, 20 091 bacteraemias comprising 22 800 blood culture isolates were diagnosed. The changes in methodology increased the recovery of some bacterial groups; the greatest impact was observed for Enterobacteriaceae, pneumococci and Staphylococcus aureus whereas recovery of β-haemolytic streptococci, Pseudomonas aeruginosa, other Gram-negative aerobes, and fungi was not affected. Changes in blood culture methodology should be taken into account when assessing time trends of bacteraemia.