さまよう薬剤師のブログ

学位を持っても、センスのない、感染制御専門薬剤師のブログ.  I have Ph.D. but less sense ID pharmacist.

Follow-up blood cultures in Gram-negative bacteremia: Are they needed?

2017年CIDに発表された、GNR血流感染のフォロー血液培養の必要性検討に関する報告。

 

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Background

Bloodstream infections remain a major cause of morbidity and mortality. Gram-negative bacilli (GNB) bacteremia is typically transient and usually resolves rapidly after the initiation of appropriate antibiotic therapy and source control. The optimal duration of treatment and utility of follow-up blood cultures (FUBC) have not been studied in detail. Currently, the management of Gram-negative bacteremia is determined by clinical judgment. To investigate the value of repeat blood cultures, we analyzed 500 episodes of bacteremia to determine frequency of FUBC and identify risk factors for persistent bacteremia.

Methods

Of 500 episodes of bacteremia, we retrospectively analyzed 383 (77%) that had at least 1 FUBC. We sought information regarding presumed source of bacteremia, antibiotic status at the time of FUBC, antibiotic susceptibility, presence of fever, comorbidities (intravenous central lines, urinary catheters, diabetes mellitus, AIDS, end-stage renal disease, and cirrhosis), need for intensive care, and mortality.

Results

Antibiotic use did not affect the rate of positivity of FUBC, unless bacteria were not sensitive to empiric antibiotic. Fever on the day of FUBC was associated with higher rates of positive FUBC for Gram-positive cocci (GPC) but not GNB. Mortality and care in the intensive care unit were not associated with positive FUBC. Seventeen FUBC and 5 FUBC were drawn for GNB and GPC to yield one positive result.

Conclusion

FUBC added little value in the management of GNB bacteremia. Unrestrained use of blood cultures has serious implications for patients including increased healthcare costs, longer hospital stays, unnecessary consultations, and inappropriate use of antibiotics.

 

Definitions

 

True Bacteremia: at least one positive blood culture, not otherwise considered a contaminant. Contaminant: a positive blood culture in which the isolate was a common skin organism (such as diphtheroids, micrococcus, or coagulase negative Staphylococcus) isolated in one bottle, or when the medical records reported the positive cultures as contaminants.

 

Persistent Bacteremia: positive blood cultures for the same original organism in a sample drawn at least 24 hours after the initial culture. We considered any positive blood culture within 24 hours of the first positive as being part of the same episode.


Medical disease (vs. Surgical Disease): disease in which the source of bacteremia does not require surgical resolution. Of note, in our series, intravenous-catheter-related infections were categorized as medical diseases, even when the resolution required the surgical removal of the source.

 

Serious Skin Infections: severe cellulitis, necrotizing fasciitis, and skin abscesses.


Febrile: Patients were considered febrile if their recorded temperature was >100.4oF when at least one of the follow up blood cultures was drawn.

 

In our cohort, approximately 5 FUBC were needed in order to yield one positive result; however, when considering only GNB bacteremia, it took 17 FUBC to yield a one positive result.

 

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Limitations

 

First, we eliminated contaminants upfront, likely skewing the distribution of the true positive cultures.

Second, the medical records examined did not offer an explanation of why the FUBC were ordered. That kind of explanation might open opportunities to educate physicians on the actual indication for blood cultures.

Third, and related to the previous one, there is no explanation on whether a perception of disease severity played a role in the decision to obtain FUBC only in 77% of our cohort, and not in all of it.

Finally, the analysis of risk factors for positive GNB FUBC is limited by the low incidence of such event.

 

感想

 

面白い検討!

心内膜炎や膿瘍を疑う以外は、グラム陰性菌のフォロー血培を主治医と相談していないのですが、今後もこの方向性で考えています。

一方、グラム陽性菌に対しては、フォロー血培の重要性を強調し、差別化を図ってます。

 

 

本日の一曲

 

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