Bacterial growth and detection in platelet products. The initial bacterial inoculum can be very small and is also infrequent, with an estimated 0.1% to 0.03% of products being microbially contaminated. Different microbial organisms have different growth curves, which affect the likelihood of detection with primary testing (unless delayed). Gram-positive, slow-growing, and limited-growth organisms can be missed on primary testing. The Gram-positive bacteria can reach concentrations above 10e5 colony-forming units (CFU/mL), which are associated with symptomatic septic reactions. The secondary testing is more likely to detect such organisms.