Publication:

Optimizing the number of blood cultures for lower and middle income countries: a large scale study in a public sector tertiary care teaching hospital of Southern India

Background Blood culture is widely accepted as the gold standard investigation for the diagnosis of blood stream infections (BSI). The number of blood cultures collected has a considerable impact on the organism isolation. This study aims to optimize the number of blood cultures needed, for an optimal diagnostic yield in BacT/ALERT VIRTUO system mainly in a resource limited setting.

Methods All the blood cultures (BCs) obtained in BacT/Alert bottles per patient during a 24-h period were included as ‘one episode’ and categorized as single bottle, 1-set (2 aerobic bottles), 2 sets and 3 sets. BC bottles were incubated in the BacT/ALERT VIRTUO (bioMérieux) for a period of five days. Bottles flagged positive were subjected to Gram staining and culture plating. Colonies grown were identified by MALDI-TOF MS, VITEK MS, bioMérieux.

Results Cumulative positivity rate increased (21.7%, 41.4%, 56.1%, 60.6%) and pathogen isolation rate increased (10.3%, 21.8%, 30.4% and 33.8%) progressively when collected in single bottle, 1, 2 and 3 sets respectively. The pathogen detection rate for GNB and GPC were 45.1% and 42.6% respectively with one bottle and this got upsurged to 85.6% and 98.9% for GNB and 83.6% and 98.2% for GPC when collected in ≤1 set and ≤2 sets respectively.

Conclusions Two BC sets over a 24-h period can detect approximately 98% of the pathogens with a cumulative positivity rate of 60% and hence it is a justifiable alternative approach to the standard practice of 3-sets of BCs.