Objective:

To investigate the number, timing and yield of mycobacterial blood cultures (BC) for the detection of Mycobacterium tuberculosis complex (MTC) in HIV-infected patients in Portugal.

Methods:

BC (Myco/F-Lytic) collected from 1998 to 2001 from HIV-infected individuals with culture proven MTC were retrospectively studied, including time and number of BC, as well as time, number, specimen type and result of all concurrent mycobacterial cultures. Conventional, non-mycobacterial BC (Bact/Alert FA) was inoculated with serial dilutions of MTB to determine the ability of MTB to grow in the medium. Subsequently, all non-mycobacterial BC (Bact/Alert FA) collected from HIV-positive patients that remained negative after 7 days of incubation in the Bact/Alert instrument were prospectively investigated for the presence of MTB by auramine staining (and culture were indicated).

Results:

In the retrospective part of the study, a total of 1181 BC from 858 patients were collected. One hundred and fifty-seven HIV-positive patients had culture proven TB (any kind of specimen). Of these, 44 patients (28%) had 48 positive BC for MTC. In 29 cases, BC were the quickest or only way to diagnosis with a mean of 22 days to positivity (range 11–46). In six of ten patients who had two or more BC collected, discordant results between the multiple BC were observed. Positive BC were collected significantly earlier during admission than negative BC from patients with extrapulmonary/disseminated TB (61% versus 19% within 48 hours, P < 0.01). The serial dilution experiments showed that the new Bact/Alert FA medium (supplement: charcoal) supports the growth of MTB down to an inoculum of less than 10 bacteria/ml and that auramine staining detected all positive BC. In the ongoing prospective part, 220 BC from 85 patients have been checked so far for the presence of mycobacteria. Five conventional BC from two patients yielded mycobacteria.

Conclusions:

BC are useful to provide rapid cultural confirmation of TB in HIV-infected patients in a setting such as Portugal. They should be collected as early as possible after admission. Interestingly, the new Bact/Alert FA medium supplemented with charcoal seems to support the growth of MTB. The ongoing investigation of non-mycobacterial BC will try to establish if a single BC is enough to detect the mycobacteraemic episode or if a collection of multiple BC, perhaps at longer intervals (>12–14 h apart), may increase yield further, as very rarely is ³1 mycobacterial BC collected.