Epididymitis is inflammation of the epididymis, which is a structure located on top of each testicle (testis). The epididymes are an important part of the sperm development process and are more prone to infection than the testicles.

Orchitis, inflammation of the testicles, usually results from the spread of infection from the epididymis. Most cases of isolated orchitis (i.e., orchitis that develops without epididymitis) are a symptom of the mumps (a viral infection that usually begins in the salivary glands). When epididymitis and orchitis occur together, it is called epididymo-orchitis.

These conditions cause inflammation and pain that is often limited to one, but can involve both sides of the scrotum.

Acute epididymitis, orchitis, and epididymo-orchitis cause sudden pain that usually responds well to treatment. Chronic conditions cause pain that develops gradually and can be more difficult to treat. Acute and chronic cases may result in male fertility problems or testosterone deficiency.

Incidence and Prevalence 
Acute epididymitis is common in young men, and can affect males of any age. Orchitis and chronic conditions are less common. According to the U.S. Centers for Disease Control and Prevention (CDC), epididymitis is especially common in young sexually-active men and is the most common cause of acute (severe) scrotal pain in adolescent males.

In 2004, the CDC noted that approximately one-third of postpubertal (sexually mature) males with mumps develop mumps orchitis, which is the primary cause of isolated orchitis. However, in a 2006 outbreak of mumps in the United States, about 50% of infected postpubertal males developed mumps orchitis, according to the CDC. Mumps is rare in the United States, due to a widely available vaccine, but occasional outbreaks do occur. It is a common disease outside of the United States.

Causes and Risk Factors

The most common cause for acute epididymitis and epididymo-orchitis is a bacterial infection that spreads from another area, usually the urinary tract (e.g., urethra, bladder). Sometimes, pain in the testicular area is the first sign of infection.

According to the CDC, approximately two-thirds of acute epididymitis cases in men under age 35 are complications of gonorrhea or chlamydia/NGU, which are sexually transmitted infections (also called as STIs or STDs).

Gonorrhea and chlamydia, which often occur together, may cause symptomatic urethral infections (urethritis). In some cases, the first symptom of gonorrhea or chlamydia infection is epididymitis.

Other than sexually transmitted infection, the most common cause for epididymitis is another type of bacteria, such as E. coli. Rare causes include systemic tuberculosis (TB), sarcoidosis, brucellosis (a rare bacterial infection), fungal infection, and infected hydrocele (an abnormal fluid-filled sac around the testicles). Systemic TB usually only occurs in people who have a compromised immunity, such as with AIDS, or in communities where TB is widespread.

Inflammation of the epididymes and testicles also may have noninfectious causes, such as trauma, recent urinary catheterization, or reflux (backwards flow) of urine caused by a bladder outlet obstruction (e.g., a result of enlarged prostate or urinary tract abnormalities). The drug amiodarone (Cordarone®), used to treat severe cases of irregular heart rhythms, also can cause inflammation of the epididymis.

Chronic epididymitis and epididymo-orchitis also can develop as a result of multiple episodes of acute cases. In some chronic cases, the cause is unknown.

Risk factors for epididymitis include the following:

  • Frequent urinary tract infections (e.g., urethritis, kidney infection)
  • Untreated bacterial prostatitis
  • Untreated bacterial STD
  • Urinary catheterization
  • Unprotected sex
  • Severely compromised immunity
  • Bladder obstruction (e.g., due to enlarged prostate or urethral abnormality)

The most common cause for acute orchitis is epididymitis, and the condition is then more accurately called epididymo-orchitis. Orchitis that occurs by itself usually is a secondary symptom of the mumps (a viral infection that usually begins in the salivary glands). This condition, which is called mumps orchitis, only occurs in males after puberty.

According to the Centers for Disease Control and Prevention (CDC), college dormitory residents, health care workers, and international travelers are at greatest risk for exposure to and infection with mumps. Mumps is common in many countries outside the United States, including Western Europe. Vaccination against mumps helps, but it is not a guarantee of prevention.