Staphylococcus aureus Prostatic abscess: a clinical case report and a review of the literature

Prostatic abscess is a rare complication of acute bacterial prostatitis, described in 0.5 to 2.5% of patients presenting with inflammatory prostatitis [1]. Patients with prostatic abscess typically present with difficulty urinating or with acute urinary retention. The most common causative pathogens include Enterobacteriaceae such as Escherichia coli [2], or in our local clinical context in northern Australia, Burkholderia pseudomallei [3]. Staphylococcus aureus, a Gram-positive coccus, is a common human pathogen, yet is a rarely reported cause of prostatic abscess [1].

The patient was a 53 year-old Indigenous Australian who presented to a remote regional hospital in northern Australia with acute onset urinary retention. His past history included type 2 diabetes mellitus, chronic hepatitis B infection and recurrent skin and soft tissue infections. He also had a history of long-term kava use.

The patient was recalled and admitted to hospital. His urinary symptoms and associated suprapubic pain persisted. He had difficulty ambulating due to pain in his left thigh. A digital rectal examination revealed a firm prostate of normal size, without tenderness, and a tender diffuse swelling was noted in the medial left thigh. A beside ultrasound of the thigh revealed a hypoechoic lesion measuring 74x52x61 mm with an estimated volume of 123 mL. The patient had blood taken for culture, was then commenced on intravenous vancomycin and then transferred by air ambulance to our institution, where he was admitted for ongoing care.

Laboratory tests on admission showed a total leucocyte count of 12.7 × 10⁹/L (neutrophil count, 8.7 × 10⁹/L) and a CRP of 65 mg/L (reference range 0.0–5.0 mg/L). Serological testing for B. pseudomallei was negative at <1:20 using indirect haemagglutination. B. pseudomallei was not isolated from throat or rectal swabs after culture in Ashdown’s medium [4]. Urine culture again isolated a pure growth of MRSA, with reported antibiotic sensitivity to clindamycin but resistance to trimethroprim. This profile is consistent with non–multidrug-resistant, methicillin-resistant S. aureus (nmMRSA; isolates being defined phenotypically as those resistant to less than 3 non–beta lactam antibiotic classes [5]). An ulcer present on the right great toe was swabbed and was also culture-positive for nmMRSA with an identical antibiogram. Skin scrapings on this admission tested positive for Sarcoptes scabei and his clinical condition was consistent with a concomitant diagnosis of crusted (previously, Norwegian) scabies. He also had an ulcer on his right great toe.

A CT scan of the abdomen and pelvis showed multiple prostatic abscesses including a prominent expansive abscess within the left base and multiple loculations within the apex (Additional file 1: Fig. S1).

At day 2 post-transfer, screening blood cultures isolated nmMRSA with the same antibiogram as was found in urine on the first assessment. Vancomycin Etest® showed an MIC of 1.5 μg/mL.

A follow-up CT scan post-drainage of the prostatic abscess showed interval improvement in the loculated right prostatic abscess; however, the left-sided collection appeared unchanged with possible enlargement (Additional file 2: Fig. S2), measuring 21 × 35 mm compared with 19 × 21 mm prior to drainage. Following three days of IV antibiotic therapy and following surgical drainage of the abscess, surveillance blood cultures were negative. Transthoracic echocardiogram showed no evidence of endocarditis.

The patient was continued on intravenous vancomycin with addition of oral clindamycin because of its recognised prostatic penetration [6]. He declined further surgical drainage options. The patient improved clinically and received a total 4 weeks of intravenous vancomycin plus oral clindamycin therapy. Repeat imaging at the completion of IV therapy showed some residual abscess collection (not shown). Further surgical intervention was discussed with the patient and was declined. Repeat imaging performed 5 months later showed the prostatic abscess had completely resolved.

Thirty nine publications were identified. After screening the titles and abstracts, 21 publications met the inclusion criteria and were thus eligible for full-text review. An additional 14 papers were identified by reference screening for further citations that met inclusion criteria. The case presented in this study has been added to studies identified in the review.

These 35 full-text papers included a total of 39 patients with a diagnosis of S. aureus prostatic abscess. With our report of a further case, this led to a review of 40 cases. The summary of the literature search is displayed in Table 1.

S. aureus is a major human pathogen that causes a wide range of clinical infections and there is a heavy burden of staphylococcal disease in Indigenous people [5]. Prostatic abscess resulting from S. aureus infection is very uncommon relative to its propensity to cause other human infections, with only 39 cases previously reported in the English language literature.

The S. aureus isolates in this case were genotyped as CC5-MRSA and carried genes for the bi-component leukocidin PVL and was resistant to trimethoprim. This has similar genotypic properties to an emerging clone in the neighbouring jurisdiction of north Western Australia [11].

From a limited sample size, it appears that with prompt identification, diagnosis and management, this condition is treatable with a low case fatality rate. However, there are no guidelines for management of S. aureus prostatic abscess. Treatment of prostatic abscesses usually involves the use of broad-spectrum antibiotics directed at Enterobacteriaceae, with or without drainage. In our experience the decision to drain an abscess depends on several factors: the size of the abscess, accessibility and ease of drainage, and the patient’s response to antibiotic therapy. The sample size of this study and methodology involved means that we cannot draw firm conclusions on the evidential basis of draining prostatic abscesses caused by S. aureus. A single-centre retrospective study of drainage in prostatic abscess recommended that trans-rectal drainage is the best option for drainage in selected cases of prostatic abscess [12].

Our case is the first report of using clindamycin step-down therapy following IV therapy. Our use of clindamycin was driven by its excellent prostatic penetration, in which prostatic levels of clindamycin have been reported to exceed that of serum levels [13]. Options for drainage of prostatic abscess include trans-rectal, trans-perineal or transurethral approaches. In the case we reported here, the abscess was drained trans-rectally and was uncomplicated in this patient.