Matters arisingassociation is influenced by the way in which the control group is selected and in this regard we question the nature of controls studied by Jensen and colleagues.It appears that none of the asymptomatic control sub- jects was examined microscopically to determine the existence of urethral polymorphonuclear (PMN) leucocytes.Indeed, men with "asymptomatic" urethritis may have been included in the control group.Few investigators have compared the prevalence of mycoplasmas in men with microscopic urethritis who have no signs or symptoms with that in men without urethritis.However, Swartz et al6 found that Chlamydia trachomatis was isolated more fre- quently from men with asymptomatic NGU than from those without objective urethritis, suggesting that urogenital pathogens may be involved in the aetiology of this condition.In addition, it is unclear whether Jensen and colleagues examined the asymptomatic subjects clinically at enrolment.Clearly, asymptomatic men with a discharge on examination and objective urethritis ( 3 5 PMN leucocytes/high-power microscopic field) have "clinical urethritis" and should be excluded from the control group and included in the studygroup.Inclusion of asymptomatic men who have objective ure- thritis, with or without an observable dis- charge, in the control group would prevent proper evaluation of negative associations.This may have influenced to some extent the significance given to M genitalium by Jensen and colleagues and biased their results against detecting an association of U ure- alyticum with NGU.
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Adrian Mindel (1994) studied this question.