Bacteraemia with an unknown focus: is the focus de facto absent or merely unreported? A one-year hospital-based cohort study.

An unknown focus of infection is associated with an increased risk of death in patients with bacteraemia. However, the implications for patient management remain uncertain, and to our knowledge, the validity of an unknown focus has not been evaluated. Therefore, we conducted a retrospective record review of bacteraemias with an unknown focus recorded in a regional bacteraemia database. The study cohort comprised 645 cases of bacteraemia diagnosed in 537 hospitalized patients at Aalborg Hospital, Denmark, in 2003. The focus was unknown in 184 (29%) bacteraemia episodes (162 patients). The record review pointed conclusively to a focus in 39 episodes. The positive predictive value of an unknown focus was 79% and the proportion of bacteraemias with a focus increased from 71% to 78%. Among the 145 cases of bacteraemia with a de facto unknown focus, there were 36 incidents of febrile neutropenia and 20 additional incidents of early death which precluded a search for a focus. The study confirmed the focus to be de facto absent in most patients classified with an unknown focus. The distribution of foci changed only marginally by the disclosure of a focus in one of five patients in the 'unknown' group.