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NHSN guidance restated on excluded organisms and when blood cultures may meet pneumonia 2 or be attributed as secondary BSI
Summary
During a 2025 NHSN training, Jennifer Watkins clarified that Candida spp., Enterococcus spp. and coagulase-negative staphylococci are excluded as pneumonia pathogens in blood unless recovered from lung tissue or pleural fluid, and explained the two secondary BSI attribution scenarios that determine when a blood culture can meet pneumonia criteria.
Jennifer Watkins of the NHSN protocol and training team reviewed laboratory elements for pneumonia 2 and 3 and clarified pathogen exclusions and how blood cultures can be used for pneumonia case definition and secondary BSI attribution.
Watkins said the pneumonia 2 and 3 algorithms include several laboratory elements and that, for pneumonia purposes, "all Candida species or yeast not otherwise specified, all coagulase negative staphylococcus species, and all enterococcus species are excluded as pathogens unless identified from lung tissue or pleural fluid." She explained the pneumonia 3 immunocompromised exception: matching Candida species recovered from a respiratory specimen and blood within the same infection window period can be used to meet pneumonia 3 for patients who meet the immunocompromised criteria.
On culture thresholds, Watkins emphasized that quantitative culture thresholds (table 5) or corresponding semi-quantitative results are required for certain lower respiratory tract specimens (bronchoalveolar lavage, protected specimen brush, endotracheal aspirate). For example, an endotracheal aspirate result must show an eligible quantity (for example, an illustrative threshold commonly used is >100,000 CFU/mL) or an acceptable semi-quantitative equivalent (e.g., "4+" or "many") to count toward pneumonia 2.
Watkins explained the two secondary BSI attribution scenarios used in practice: scenario 1 requires a matching organism when the blood specimen is collected in the secondary BSI attribution period but outside the pneumonia infection window; scenario 2 applies when the blood specimen collection date falls within the pneumonia infection window and the blood culture itself can serve as the laboratory element to meet pneumonia 2. She illustrated both with case studies showing how events are reported and when a BSI is attributed as secondary to a pneumonia event.
Watkins also reminded attendees that excluded organisms identified in blood during the secondary BSI attribution period can only be attributed as secondary to pneumonia when a matching organism is identified from lung tissue or pleural fluid; otherwise those organisms should be accounted for as primary BSIs or secondary to another site-specific infection.
