February 24, 2021
Reviewed by Lauren Richey, MD, MPH, FIDSA
Septic shock from gram-negative bacteremia carries a mortality rate of nearly 40%. The role of follow-up blood cultures has been established in other causes of bacteremia but their role in the management of gram-negative bacteremia is still not clear. An article in Clinical Microbiology and Infection describes an observational cohort study of over 1,700 patients admitted from 2002 to 2015 at Duke Health System with gram-negative bacteremia. The study objective was to determine risk factors associated with acquisition of follow-up blood cultures and risk of in-hospital mortality. Follow-up blood cultures were defined as a blood culture drawn from 1 to 7 days after the initial positive culture.
Sixty-eight percent of patients in the cohort had follow-up blood cultures. Patients who had Pseudomonas and Serratia species in their original cultures were more likely to have follow-up cultures. Twenty percent had positive follow-up blood cultures (persistently positive cultures), and compared to those with negative cultures, they were less likely to be receiving effective antibiotic therapy, more likely to have a cardiac device, be hemodialysis dependent, and have an endovascular source. Patients with follow-up blood cultures had lower rates of all-cause in-hospital mortality (15% versus 20%, P = .01) and attributable in-hospital mortality (8% versus 15%, P < .0001) than those who did not get a follow-up culture. Patients with positive follow-up blood cultures had increased all-cause mortality (21% versus 11%, P = .0005) and attributable mortality (12% versus 7%, P = .01) compared to those with negative cultures. The patients without follow-up blood cultures had similar all-cause mortality to those with positive cultures (20%).
The authors conclude that positive follow-up blood cultures were common (20%) in gram-negative bacteremia and that those who were persistently positive were often on effective antibiotic therapy (> 50%). These patients with persistent bacteremia were found to be at a higher risk for death than those who had negative cultures. Collecting the follow-up cultures can lead to the identification of these high-risk patients and allow for more aggressive diagnostic and therapeutic strategies.