Sterility is the inability to produce offspring. Orchitis is inflammation of the testis, which is manifested by swelling and tenderness and is usually of infectious origin, such as tuberculosis, mumps, enterovirus, syphilis, or certain fungal diseases. Orchitis is also referred to as testitis, didymitis, and orchiditis. No population-based incidence rates were identified.
There is no suspected association between measles vaccine alone and orchitis or sterility. The possibility of an association between mumps vaccine and sterility secondary to orchitis has been suspected on the basis of reports of orchitis following infection with wild-type mumps virus.
There are no data bearing directly on the biologic plausibility of an association of orchitis or sterility with measles vaccine. The most compelling argument for biologic plausibility regarding orchitis following mumps vaccine are the reports of orchitis following infection with the wild-type mumps virus. In 1950, Werner (1950a) reported that mumps is complicated by orchitis in one-fifth of all cases of mumps occurring in males after puberty. He also found that mumps orchitis had been the cause of testicular atrophy in 43 percent of 44 cases of obvious testicular atrophy found in an examination of 2,000 random males 14 to 34 years of age. In another study, he analyzed seminal fluid from 49 males with a past history of mumps orchitis (Werner, 1950b). The age of onset of orchitis ranged from 10 to 27 years, with a median age of 16 years. The interval between the onset of orchitis and the study ranged from a few months to 9 years, with a median of 4 years. Some degree of testicular atrophy was apparent in 39 of 49 patients. Some 51 percent of 49 patients from 18 to 27 years of age with a past history of mumps orchitis had semen with mean sperm counts and motilities that were lower than those for semen from control subjects. Only one man had azoospermia. Testicular atrophy was no more common among patients with abnormal semen specimens than it was in the group with orchitis as a whole. Mumps orchitis was felt, on the basis of seminal fluid examination, to have impaired fertility in 13 percent of the individuals with a past history of the disease. Werner (1950b) concluded that since only 1.7