BACKGROUND: The purpose of this study was to analyse the effect of a history of febrile illness on semen quality.

METHODS: Twenty-seven healthy men (median age 24.4 years) were followed with monthly semen samples and a daily record of the occurrence of experienced febrile episodes over a 16 month period between March 1998 and June 1999 in Copenhagen, Denmark. Semen samples were analysed for semen volume, sperm concentration, percentage immotile sperm and percentage morphologically normal sperm.

RESULTS: Sperm concentration significantly decreased by 32.6% (95% confidence interval -49.9; -9.2) following fever during meiosis and by 35.0% (-50.5; -14.6) following fever during the postmeiotic period of spermatogenesis (spermiogenesis). The percentage of morphologically normal sperm was decreased by 7.4% (-11.6; -3.0) and the percentage of immotile sperm was increased by 20.4% (6.0; 36.8) by fever during spermiogenesis. The number of days the men experienced fever significantly affected their semen parameters. Thus fever during meiosis and spermiogenesis reduced sperm concentration with respectively 7.1% (-12.9; -0.9) and 8.5% (-13.6; -3.0) per day of fever. The percentage of morphologically normal sperm decreased 1.6% (-2.5; -0.6) and the percentage of immotile sperm increased 4.5% (1.7; 7.3) per day of fever during spermiogenesis. There was, however, a large variation in the individual response to fever.

CONCLUSIONS: Sperm concentration, morphology and motility in a semen sample are adversely affected by a febrile episode during the postmeiotic period of spermatogenesis (spermiogenesis). Sperm concentration was also adversely affected by fever during the period of meiosis, whereas fever at other time points during spermatogenesis did not seem to significantly affect these sperm parameters. The adverse effect seemed to be dependent upon the number of days with fever.