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This review describes the microbiology, diagnosis and management of bacteremia caused by …

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- Clinical review: Bacteremia caused by anaerobic bacteria in children

The source of anaerobic bacteremia is generally clinically suspected, so therapy with antimicrobial agents active against anaerobes is often instituted empirically. Empirical therapy may provide coverage for anaerobes in only half of the patients with anaerobic bacteremia, and failure to pay attention to the results of anaerobic blood cultures may have serious consequences [53].

Mortality as a result of anaerobic bacteremia remains high. Risk factors for a fatal outcome include compromised status of the host, advanced age, inadequate or no surgical therapy, and the presence of polymicrobial sepsis. Additionally, mortality varies between the infecting B. fragilis group species [53,54]. Bacteroides fragilis is the most common anaerobic isolate in these studies [53,54], with associated mortality between 24% and 31%, while the mortality associated with B. thetaiotaomicron bacteremia ranges between 38% and 100%, and that associated with B. distasonis bacteremia is about 50%. Whether these differences are the result of differences in virulence factors such as endotoxins, encapsulation, host defenses, or differences in antimicrobial susceptibility remains unknown.

The mortality following anaerobic bacteremia varies. In one study [17] it was 18% (five of 28 patients) and depended on such factors as age of the patient, underlying disease, nature of the organism, speed of diagnosis, and surgical or medical therapy instituted. This mortality rate is similar to that reported in adults [13]. Of the three infants who died, two were newborns and one was 8 months old. Four patients were infected with organisms of the B. fragilis group that were resistant to penicillin; inappropriate antimicrobial therapy was administered to two of these patients, owing to the length of time needed for identification of the organisms, and the other two patients had underlying disorders that further aggravated their condition. The fifth child who died had a ventriculoatrial shunt that was infected with P. acnes, in addition to severe hydrocephalus and mental retardation.

Certain other serious concomitant sites of infection can be present in children with anaerobic bacteremia. Most of these sites serve as the source of the infection, however others may represent a site of secondary hematogenous spread of the organism(s). The most frequent conditions are meningitis, peritonitis, subdural empyema, and septic shock. Although some of the children with these infections may become seriously ill, most will respond well to surgical and medical therapy.

In five (18%) of the children included in the report by Brook and co-workers [17], meningitis occurred that was associated with B. fragilis (two children), P. acnes (two children), and Peptostreptococcus species (one child). A direct extension of the organism from an infection site to the meninges might have occurred in two of these children, both of whom had surgical drainage of local collection of pus. One of these children had pansinusitis and required a Caldwell–Luc procedure, where a direct extension of the inflammation to the sub-dural space through the cribriform plate was demonstrated. Ethmoid drainage and frontal craniotomy yielded pus from the sinus as well as from the subdural space.

Anaerobic organisms recovered from blood were isolated from other infected sites in 16 (57%) of the patients reported by Brook and coworkers [17]. In eight of the 16 patients, anaerobic bacteria were mixed with other anaerobic and/or with aerobic organisms (two to five bacteria/specimen of pus). Extravascular sites from which anaerobic organisms were recovered included abscesses (four patients), cere-brospinal fluid (three patients), peritoneal fluid (four patients), tracheopulmonary aspiration (two patients), sinuses (two patients), and sinus and subdural empyema (one patient). Seven of the eight children who had soft-tissue abscesses or local collections of pus required surgical drainage. Some of these children had recurrent or persistent bacteremia until proper surgical drainage was performed. Four patients also had extravascular collections of pus, however anaerobic organisms were not recovered from these sites, either because anaerobic cultures were not obtained or because the specimens were inappropriately transported.

Shanks and Berman reported two children with multiple pulmonary abscesses who developed hematogenous spread from head and neck infections [55]. Porphyromonas asac-charolytica was isolated from the blood of one child, and B. fragilis from the other child.

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