Acute Bacterial Prostatitis 

The prostate is an extraperitoneal organ that encircles the neck of the bladder and urethra and weighs approximately 20 g in a healthy man. In an adult, this organ is divided into 4 distinct zones or regions: the periurethral, central, transitional, and peripheral zones. Prostate carcinoma arises more often in the peripheral zone than the other zones. However, the distribution of prostatic inflammation among the various zones is not clear.

Prostatitis is the most common urologic diagnosis in males younger than 50 years and the third most common diagnosis in men older than 50 years (after benign prostatic hyperplasia [BPH] and prostate cancer). Acute prostatitis is rare and presents as an acute urinary tract infection (UTI) in men. Although this condition is much less common than chronic prostatitis, acute prostatitis is easier to identify because of its more uniform clinical presentation. Approximately 5% of cases of acute bacterial prostatitis (ABP) progress to the chronic condition,^[1] which has several classifications and is poorly understood, partly because of its uncertain etiology and lack of clearly distinguishing clinical features.

Acute prostatitis is usually associated with predisposing risk factors, including bladder outlet obstruction secondary to BPH or an immunosuppressed state. This review focuses on acute bacterial prostatitis (ABP).

Pathologic definition of prostatitis

Pathologically, prostatitis is defined as an increased number of inflammatory cells within the prostate gland. The inflammatory process may be infectious or inflammatory in origin. The most common histologic pattern is a lymphocytic infiltrate in the stroma immediately adjacent to the prostatic acini (see the image below).^[2]

Prostatitis occurs in distinct forms that have separate causes, clinical features, and outcomes. Four clinical entities have been described: acute bacterial prostatitis, chronic bacterial prostatitis, nonbacterial or abacterial prostatitis, and prostatodynia.

NIH classification and definition of prostatitis

The National Institutes of Health (NIH) classification and definition of the categories of prostatitis are as follows:

• Category I – Acute bacterial prostatitis (ie, acute infection of the prostate)
• Category II – Chronic bacterial prostatitis (ie, recurrent urinary tract infection and/or chronic infection of the prostate)
• Category III – Chronic abacterial prostatitis/chronic pelvic pain syndrome (ie, discomfort or pain in the pelvic region for at least 3 mo with variable voiding and sexual symptoms and/or no demonstrable infection. By definition, the syndrome becomes chronic after 3 mo.)
• Category IIIA – Inflammatory chronic pelvic pain syndrome (ie, white blood cells in semen and/or expressed prostatic secretions and/or third midstream bladder specimen)
• Category IIIB – Noninflammatory chronic pelvic pain syndrome (ie, no white blood cells in semen and/or expressed prostatic secretions)
• Category IV – Asymptomatic inflammatory prostatitis (ie, evidence of inflammation in biopsy samples, semen and/or expressed prostatic secretions, and no symptoms)

Historical and epidemiologic data

In 1978-1979, symptoms due to acute and chronic prostatitis accounted for 25% of outpatient urinary conditions in the United States. In 1985, according to Nickel, acute and chronic prostatitis accounted for more office visits than BPH or prostate cancer. Most of these visits were for chronic prostatitis. In the early 1990s, the diagnosis of prostatitis resulted in slightly more than 2 million office visits per year.^[3]

The international prevalence rate of prostatitis is similar to that in the United States. In one report, of 600 men diagnosed with prostatitis, 5% had bacterial prostatitis, 64% had nonbacterial prostatitis, and 31% had pelvic-perineal pain syndrome or prostatodynia.

For patient education information, see Men's Health Center, as well as The Male Anatomy, and Prostate Infections (Prostatitis).

See also the following:

• Prostatitis
• Chronic Bacterial Prostatitis
• Chronic Pelvic Pain in Men
• Granulomatous Prostatitis
• Nonbacterial Prostatitis

Several theories exist regarding the pathogenesis of acute bacterial prostatitis, including intraprostatic urinary reflux, ascending urethral infection, direct invasion or lymphogenous spread from the rectum, and direct hematogenous infection.

This Intraprostatic urinary reflux theory is the most widely accepted. Infected urine refluxes into the ejaculatory and prostatic ducts that empty into the posterior urethra. Because of the anatomy of the prostate gland, ducts that drain glands in the large peripheral zone are positioned more horizontally than other prostatic ducts and, thus, facilitate the reflux of urine into the prostate. Consequently, most infections occur in the peripheral zone.

In younger men, ascending urethral infection may occur following sexual intercourse. Meatal inoculation may occur during unprotected anal intercourse, instrumentation, and prolonged catheterization.

The organisms primarily responsible for acute bacterial prostatitis (ABP) are also those responsible for most urinary tract infections; these include gram-negative members of the Enterobacteriaceae family such as Escherichia coli, Proteus mirabilis, Klebsiella species, Enterobacter species, Pseudomonas aeruginosa, and Serratia species. Of these, E coli is involved most often and has been shown to increase biofilm formation.^[4] Most prostatic infections (82%) involve only a single bacterial organism. In some cases, 2 or 3 strains of bacteria may be involved.

Obligate anaerobic bacteria and gram-positive bacteria other than enterococci rarely cause acute bacterial prostatitis. Enterococci account for 5-10% of documented prostate infections.^[5] Staphylococcus aureus infection due to prolonged catheterization may occur in the hospital. Other occasional causative organisms include Neisseria gonorrhea,Mycobacterium tuberculosis,Salmonella species, Clostridium species, and parasitic or mycotic organisms. N gonorrhea should be suspected in sexually active men younger than 35 years.

If recurrent urinary tract infections are confirmed, patients need to be evaluated for any structural abnormality.

Risk factors

The following are risk factors for acute bacterial prostatitis (all allow bacterial colonization):

• Intraprostatic ductal reflux
• Phimosis and redundant foreskin
• Specific blood groups^[6]
• Unprotected anal intercourse
• Urinary tract infections
• Acute epididymitis
• Indwelling Foley catheter and condom catheter
• Transurethral surgery
• Altered prostatic secretions

If the initial response to medical therapy for acute bacterial prostatitis (ABP) is favorable, the patient's prognosis is very good. Decreased fertility has been reported, but only in cases of massive bacterial inoculation. Decreased sperm viability, including impaired motility and agglutination, has been reported in samples that contained more than 10⁶ colony-forming units (CFU)/mL of bacteria.

Prostatic abscess is an uncommon but well-described complication of acute bacterial prostatitis. Although very rare, it usually occurs in patients who are immunocompromised, who have diabetes, who have urethral instrumentation or a prolonged indwelling urethral catheters, or who are on maintenance dialysis. Coliform bacteria, especially E coli, cause more than 70% of prostatic abscesses.

Other potential sequelae of acute bacterial prostatitis include progression to chronic prostatitis, septicemia, pyelonephritis, and epididymitis.