Staphylococcus saprophyticus is one of the coagulase-negative staphylococci. It commonly causes urinary tract infection (UTI) in young sexually active women. Its role in causing UTI in men is not well defined, although data are emerging. Here we report a case of elderly man who had UTI caused by S. saprophyticus. We also reviewed medical literature on this infection.
A 90-year-old nursing home resident with history of dementia presented with suprapubic pain of 1-day duration. He also vomited once 2 hours before transfer to hospital. He was also found to have low blood pressure of 60/40 mm Hg at nursing home. Review of system was negative for other symptoms. On admission, he appeared ill. He was afebrile, and his blood pressure was 110/60 mm Hg after 1 L of fluid resuscitation during transfer. His other vitals were stable. His physical examination was unremarkable except for the presence of foley catheter that he had for a long time because of his underlying mental condition. Laboratory workup revealed high white blood cell count of 27×109/L and urine analysis consistent with UTI (positive leukocyte esterase, many white blood cells, and many bacteria). The chest radiograph was normal. Patient was started on intravenous gatifloxacin for urosepsis. The blood cultures (2/2) were negative, but urine culture grew >105 colonies of S. saprophyticus with sensitivity pattern as shown in Table 1. Patient responded very well to treatment with resolution of symptoms within 24 hours.
Pereira described novobiocin-resistant coagulase-negative staphylococci from bacteriuric patients in 1962.1 Mitchell identified these organisms from women with UTI and placed them in micrococci subgroup.2 These were reclassified and renamed as Staphylococcus saprophyticus in 1974.3 In 1970s, these were recognized as cause of uncomplicated UTI in women.4 They are responsible for 7% to 30% of UTI in women, second only to Escherichia coli.
Kauffman et al5 cultured 9314 urine specimens from male patients and isolated coagulase-negative staphylococci from 143 specimens (121 patients). However, only 3 isolates (2 patients) grew S. saprophyticus. Hovelius et al6 reported frequency of isolate as 0.5% in their series. Therefore unlike in women, S. saprophyticus rarely causes UTIs in men. Because it is a colonizer of skin, UTI by this organism is believed to be of endogenous origin with ascending infection.
UTIs caused by S. saprophyticus in men differ from their counterparts in various aspects including age, seasonal variation, and clinical characteristics. Unlike young women, it causes UTIs in elderly men. In one series, median age of patients was 70 years.6 In men, there is no seasonal predisposition. In females, incidence is generally higher in summer and fall, then in the winter and spring.4 Although no reason has been found so far, it is possible that because of salt-tolerant nature of this organism, sweating in summer and fall is favorable for colonization or infection.7
Of the male patients, approximately 50% are hospitalized, while females are almost entirely outpatients.6 Evidences suggest that about 75% of patients have predisposing cause or have undertaken iatrogenic measures, and almost half of patients have indwelling foley catheters.6-8 Thus, although S. saprophyticus causes uncomplicated UTI in women, it causes complicated UTI in men. The reason for this variation is unclear and warrants further investigation.
In addition to UTIs, it may be an important pathogen in bacterial prostatitis.9 In one series, it was isolated from urethral specimens of 35/170 men with symptoms of urethritis, suggesting that it may be an etiologic agent in some cases of nongonococcal urethritis.10
The clinical features of S. saprophyticus resemble those of other UTIs. Bacteremia and systemic toxicity are rare even when upper UTI occurs. In our review of literature, we did not find any report of bacteremia in male patients who have UTI by S. saprophyticus. Our patient also has negative blood cultures.
Microbiologically S. saprophyticus can be easily differentiated from other coagulase-negative staphylococci by testing for novobiocin resistance.11 This test has been validated in many studies. It has emerged as rapid and cost-effective screening method.
It is sensitive to most antibiotics used to treat UTI except nalidixic acid. Ishihara et al7 reported resistance of S. saprophyticus strains to ampicillin, ceftazidime, cefixime, aztreonam, and fosfomycin. There was also no difference in resistance rate on basis of gender. Our isolate was also resistant to β-lactam antibiotics in accordance to other case reports.
To summarize, S. saprophyticus is rare but important cause of UTIs in both genders. It should be part of differential diagnosis in complicated UTIs in elderly men. Whether to screen for and eradicate this organism before invasive urogenital procedures in high-risk male patients remains open-ended question, and more studies are needed to answer this.
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