Elsevier

Journal of Infection

Volume 64, Issue 1, January 2012, Pages 41-46
Journal of Infection

Clinical significance of Staphylococcus aureus bacteriuria in a nationwide study of adults with S. aureus bacteraemia

https://doi.org/10.1016/j.jinf.2011.10.009Get rights and content

Summary

Objectives

To evaluate the clinical significance of Staphylococcus aureus bacteriuria (SABU) in adults with S. aureus bacteraemia (SAB).

Methods

All individuals ≥18 years old diagnosed with SAB in Iceland between December 1st 2003 and November 30th 2008 were retrospectively identified. Data was collected from medical records. Concomitant SABU was defined as growth of S. aureus in a urine sample taken within 24 h of the index blood culture.

Results

SABU was seen in 27 of 166 (16.3%) SAB patients having urine cultured before administration of antibiotics, but after excluding those with SAB of urinary tract origin SABU was seen in 16 of 152 (10.5%). In this latter cohort SABU was independently associated with having endocarditis (RR 6.68; 95% CI 1.53–17.3) and admission to intensive-care unit (RR 2.84; 95% CI 1.25–4.44), while for having complicated SAB the RR was 1.56 (95% CI 0.96–1.80). No correlation was seen with mortality or relapse rates.

Conclusions

SABU appears to be secondary to SAB in some cases while it is the primary infection causing SAB in others. In patients with SAB of non-urinary tract origin SABU should probably be regarded as distant haematogenous seeding and a marker of deep tissue dissemination, thus affecting general management and treatment duration.

Introduction

Staphylococcus aureus is a major pathogen of both nosocomial and community acquired blood stream infections.1, 2 S. aureus bacteraemia (SAB) has a reported mortality rate of up to 40%.3, 4, 5, 6, 7, 8, 9 It is in addition often associated with complicated infections such as endocarditis, thus requiring prolonged hospital stay and antibiotic therapy.4, 8, 9, 10, 11

S. aureus bacteriuria (SABU) in association with SAB is well documented.12, 13, 14, 15, 16, 17 S. aureus is a recognized cause of colonization or infection of the urinary tract in patients with indwelling catheter or recent urinary tract instrumentation, and occasionally this is thought to cause SAB.12, 13, 18, 19, 20, 21, 22 Another possible mechanism for concomitant SABU is that the SAB causes secondary bacteriuria by haematogenous seeding, although this theory has been questioned.13 In patients with SAB the clinical significance of SABU is not well understood. Recently it has been associated with complicated SAB16, 17 and correlation to poor clinical outcome has even been suggested.14, 17, 23, 24 Theses studies have however not attempted to distinguish between the two possible underlying mechanisms for the bacteriuria.

The objective of this population based study was to evaluate the clinical significance of SABU in adults with SAB, with a special focus on those with SAB not originating from the urinary tract. Its association with endocarditis, complicated bacteraemia and outcome (admission to intensive care unit (ICU), mortality and relapse rates) was to be assessed.

Section snippets

Study population and protocol

Iceland is an island in the North-Atlantic with a population of just over 300,000. A university hospital is located in the capital Reykjavik and a teaching hospital in Akureyri, both including a clinical microbiological laboratory. Smaller regional hospitals send collected blood cultures to either of the two laboratories, while urine cultures are usually processed locally. Blood cultures yielding S. aureus between December 1st 2003 and November 30th 2008 were identified retrospectively by the

Results

In the study period 300 individuals with SAB were identified. One additional blood culture with S. aureus was considered contamination and excluded. Basic demographic characteristics were gathered for all the patients and complete medical records were available for 299 of 300 (99.7%). In 199 of 300 cases (66.3%) a urine culture was performed within 24 h of the SAB, but 33 of those had unreliable culture results as antibiotics had already been administered at the time of culture. All 166

Discussion

In this nationwide retrospective study a concomitant SABU was seen in 16.3% of all SAB episodes and in 10.5% of episodes not being of urinary tract origin, where it was associated with ICU-admission and having endocarditis. In previous studies concurrent SABU has been found in 15–34% of all SAB patients.12, 13, 14, 15, 16, 17 In the study by Ekkelenkamp et al. SABU was seen in 7.8% (12 of 153) of SAB cases of non-urinary tract origin but in only 2.5% (2 of 79) if patients with intravesical

Financial support

Grant by the Scientific Trust of Landspitali University Hospital, which had no involvement in the study design; in the collection, analysis or interpretation of data; in the writing of the manuscript; or in the decision to submit the manuscript for publication.

Potential conflicts of interest

All authors report that they do not have a commercial or other association that might pose a conflict of interest.

Acknowledgements

The authors thank Sigurdur Heiddal MD at the Department of Internal Medicine, Akureyri Hospital as well as M. Linda Helgadottir and Holmfridur Jensdottir biomedical scientists at the Department of Clinical Microbiology, Landspitali University Hospital, for their help with data collection.

The authors had no writing assistance.

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