VOL 50: JUNE • JUIN 2004d Canadian Family Physician • Le Médecin de famille canadien 879
CME
rinary tract infections (UTI) are com- monly encountered by family physicians;
Staphylococcus aureus accounts for only 0.5%
to 6% of all positive urine cultures.1-4 Traditionally, physicians have tended to undertreat S aureus bac- teriuria due to its reputation as a common contami- nant.2,4 Th is might not be true, however, and delayed treatment could lead to development of staphylococ- cal bacteremia, a serious life-threatening illness.1,5-6
Paradoxically, S aureus bacteriuria can be an early diagnostic indicator of pre-existing staphy- lococcal bacteremia, which creates a dilemma in both investigation and treatment. The following case describes a patient diagnosed with S aureus bacteremia whose initial presentation was that of uncomplicated UTI.
Case description
A 40-year-old man went to his family physician with a 2-week history of dysuria, decreased urinary stream, and intermittent fever. His medical history included eczema and one episode of nephrolithiasis.
He took no medications and had no history of UTI.
Physical examination was unremarkable. Results of
urinalysis were positive for blood, nitrites, and leu- kocytes. Th e patient was started on 500 mg of oral ciprofl oxacin twice daily for 7 days (for a presumed diagnosis of prostatitis). Th e urine culture showed S aureus sensitive to ciprofl oxacin.
After completing a course of antibiotics, the patient returned to his family physician still feeling unwell.
Although his urinary symptoms had resolved, he was still intermittently febrile (up to 39.5C) and had devel- oped chills, sweats, myalgia, and light-headedness. He was referred to the emergency department for further investigation. Routine bloodwork and a chest x-ray examination showed no abnormalities, but blood cul- tures were positive for S aureus.
Th e patient was admitted to hospital and under- went investigation for complications associated with S aureus bacteremia. A gallium bone scan and com- puted tomography scans of his chest, abdomen, and pelvis, and testing for evidence of osteomyelitis or abscesses, were negative. Transthoracic and trans- esophageal echocardiograms did not reveal any valvular vegetations associated with endocarditis.
Th e patient improved several days after beginning a course of intravenous cloxacillin. Posttreatment urine and blood culture results were negative.
Discussion
To better understand the relationship between S aureus bacteriuria and bacteremia, we searched MEDLINE (English only) from 1970 to July 2003 for articles having the MeSH terms “bacteriuria,”
“Staphylococcus aureus,” or “bacteremia.” We found four retrospective studies focused primarily on the clinical signifi cance of staphylococcus bacteriuria with and without accompanying systemic infection.
None studied outpatients in primary care.
Many physicians tend to disregard S aureus bac- teriuria as a contaminant. In three separate studies,
Case Report:
Staphylococcus aureus bacteriuria
Important indicator of coexistent bacteremia?
Allan K. Grill, MD, CCFP Sharon Domb, MD, CCFP
Dr Grill was a second-year resident in the Department of Family and Community Medicine at the University of Toronto in Ontario when this article was written. He is now a Frank Knox Fellow at the Harvard School of Public Health, working on his Master’s degree in Public Health. Dr Domb is Medical Director of the Department of Family and Community Medicine at Sunnybrook and Women’s College Health Sciences Centre and an Assistant Professor of Medicine at the University of Toronto.
This article has been peer reviewed.
Cet article a fait l’objet d’une évaluation externe.
Can Fam Physician 2004;50:879-880.
rinary tract infections (UTI) are com- monly encountered by family physicians;
Staphylococcus aureus to 6% of all positive urine cultures.
U
880 Canadian Family Physician • Le Médecin de famille canadien dVOL 50: JUNE • JUIN 2004
the percentage of patients with documented S aureus bacteriuria (105 to 108 colony-forming units/mL) who were treated ranged from only 39%
to 74%.1-2,4 Studies have shown that 5.5% to 8.3% of patients with staphylococcal UTI who go untreated develop secondary bacteremia.1 While a primary S aureus UTI simply requires a course of oral anti- biotics, patients with secondary bacteremia require intravenous antibiotics and multiple investigations to rule out secondary complications, which include endocarditis, osteomyelitis, and septic shock.1,5-6
Staphylococcal UTI can also result from an exist- ing primary systemic bacterial infection. A study of patients with S aureus bacteremia showed that 17%
subsequently developed bacteriuria.2 Secondary bacteriuria can occur through hematogenous seed- ing of S aureus to the kidneys and urinary tract.2-4
It is challenging for physicians to know when treat- ing a UTI alone, without further investigation for coex- istent bacteremia, is suffi cient; therefore, it is important to recognize predisposing factors for primary staphylo- coccal bacteriuria, which include nosocomial causes (eg, indwelling catheters, instrumentation, surgery) and obstructive disease (eg, benign prostatic hypertrophy, stricture, malignancy).1 Similarly, identifi able causes of primary staphylococcal bacteremia include indwelling foreign bodies (eg, catheters, pacemakers), intravenous drug use, infected skin lesions, and respiratory tract infections. Immunocompromised people, hemodialy- sis patients, and cancer patients are also at higher risk of systemic staphylococcal infection.5-6
It is still unclear whether this patient’s S aureus bacteremia preceded or resulted from a staphylococ- cal UTI. We suspect that the bacteriuria was second- ary because no predisposing factors were identifi ed that could explain his urinary symptoms, and because prompt antibiotic treatment should have prevented a secondary bacteremia. While no portal of entry was found to help identify the initial source of bacteremia, this outcome is consistent with most community- acquired cases of S aureus bacteremia.5-6
Conclusion
Th is case exemplifi es the diagnostic dilemma for physicians when faced with a urine culture posi- tive for S aureus. Presence of S aureus in the urine
results from either a primary (ascending) UTI or as a consequence of bacteremia with secondary hema- togenous spread to the kidneys.1-5 Th e challenge for physicians is to recognize and treat uncomplicated S aureus bacteriuria, while at the same time being alert to the possibility of an underlying systemic infection. While management of these two scenar- ios diff ers dramatically, their clinical presentation can be indistinguishable. Identifi able risk factors for each are helpful, but by no means defi nitive.
Th erefore, if the cause of S aureus bacteriuria is unclear, physicians should consider further investi- gations to rule out a coexisting bacteremia because early diagnosis and treatment can be life saving.
Correspondence to: Dr Allan K. GrillandDr Sharon Domb, Department of Family and Community Medicine, Sunnybrook and Women’s College Health Sciences Centre, Room A-120, 2075 Bayview Ave, Toronto, ON M4N 3M5;
telephone (416) 480-4939; fax (416) 480-6038; or e-mail allan.grill@utoronto.ca or sharon.domb@sw.ca.
Competing interests None declared References
1. Arpi M, Renneberg J. Th e clinical signifi cance of Staphylococcus aureus bacteriuria. J Urol 1984;132:697-700.
2. Lee BK, Crossley K, Gerding DN. Th e association between Staphylococcus aureus bacteremia and bacteriuria. Am J Med 1978;65:303-6.
3. Demuth PJ, Gerding DN, Crossley K. Staphylococcus aureus bacteriuria. Arch Intern Med 1979;139:78-80.
4. Sheth S, DiNubile MJ. Clinical signifi cance of Staphylococcus aureus bacteriuria without concurrent bacteremia. Clin Infect Dis 1997;24:1268-9.
5. Jensen AG, Wachmann CH, Espersen F, Scheibel J, Skinhoj P, Frimodt-Moller N. Treatment and outcome of Staphylococcus aureus bacteremia: a prospective study of 278 cases. Arch Intern Med 2002;162:25-32.
6. Weems JJ Jr. Th e many faces of Staphylococcus aureus infection. Recognizing and managing its life- threatening manifestations. Postgrad Med 2001;110(4):24-36.
results from either a primary (ascending) UTI or as
EDITOR’S KEY POINTS
• Although many physicians consider urinary tract infections with Staphylococcus aureus to be of little concern, this might not be true, and they need a second look.
• Urinary tract infections with S aureus might be a sign of S aureus bacteremia; patients should be evaluated with this in mind.
POINTS DE REPÈRE DU RÉDACTEUR
• Les infections urinaires à staphylocoque doré sont considérées par de nombreux médecins comme plutôt bénignes, mais elles pourraient nécessiter plus d’attention.
• Dans certains cas, les infections urinaires à staphylocoque signalent une bactériémie à staphylocoque doré, une possibilité dont il fau- drait tenir compte.
