Infections may affect fertility, whether as standalone bacterial, viral or fungal infections or in combination. A standard urine test will screen for chlamydia, which can be treated with antibiotics.^10,17

However, a systematic review has found no clear evidence supporting a link between most types of sexually transmitted infections (STIs) and male infertility, other than with Ureaplasma and Mycoplasma.¹⁸

The presence of a wide range of viruses in semen has been associated with reduced fertility, such as cytomegalovirus, herpes simplex, human papilloma virus (HPV), hepatitis (B, C and E especially), human immunodeficiency virus (HIV) and zika virus.^18,19

Viral anti-fertility activity includes reducing sperm motility, increasing sperm abnormalities, decreasing ejaculate volume, adversely affecting reproductive hormonal secretions, damaging or scarring tissues (which may also block tubules/secretory pathways), or causing blood to be present.^17,18

Up to a third of men experiencing a mumps virus infection develop testicular inflammation (orchitis), with the testicles atrophying in up to half of these cases. Influenza viruses can reduce sperm fertility due to fever and DNA damage, reducing sperm count and motility, and reducing ability for the sperm to penetrate the egg.¹⁷