Occult bloodstream infections in adults: a "benign" entity

Patients with septic episodes whose blood cultures turn positive after being sent home from emergency departments (EDs) are recognized as having occult bloodstream infections (BSI). The incidence, etiology, clinical circumstances, and outcome of occult BSI in children are well known, but, to our knowledge, data in adult patients are scarce. We analyzed the episodes of occult BSI in adult patients at our institution.

This is a retrospective cohort study (September 2010 to September 2012), in adult patients discharged from the ED in whom blood cultures turned positive. Patients were evaluated according to a preestablished protocol.

We recorded 4025 cases of significant BSI in the ED and 113 patients with adult occult BSI. In other words, the incidence of occult BSI in the ED was 2.8 per 100 episodes. The predominant microorganisms were gram-negative bacteria (57%); Escherichia coli was the most common (41%), followed by gram-positive bacteria (29%), anaerobes (6.9%), polymicrobial (6.1%), and yeasts (0.8%). The most frequent suspected origin was urinary tract infection (53%), and most infections were community acquired (63.7%). Of the 105 patients that we were able to trace, 54 (42.5%) were asymptomatic and were receiving adequate antibiotic treatment at the time of the call, and 65 (51.2%) had persistent fever or were not receiving adequate antibiotic treatment.

Occult BSI is relatively common in patients in the adult ED. Despite the need for readmission of a fairly high proportion of patients, occult BSI behaves as a relatively benign entity.