RESUMO
In the present retrospective register study a very large data base consisting of screening audiograms obtained at military conscription of 18-year-old Swedish men was used. The study group comprised 450,175 men, aged 18 years, tested at conscription to military service. There were nine age groups covering a 24-year period, from 1971 to 1995. This database was compared with a number of different pre- and postnatal factors with possible influence on the hearing function. This ecologic methodology gives tentative clues (but no proof) of possible ototraumatic influences. The hearing capacity was fairly similar during the entire span of the study and only small variations were observed. There was a slight tendency of better hearing capacity in the later age groups, compared with the earlier ones. The mean thresholds of the frequencies 4 and 6 kHz were slightly elevated in 1971, 1976 and, to some extent also in 1992. We tried to calculate the levels of leisure noise exposure during the study period. There was no apparent tendency of reduced noise levels, on the contrary the noise levels seemed to increase. The treatment programmes for acute otitis media (AOM) underwent considerable changes during the period from the early fifties to the early eighties, when the participants were pre-school children. One possible explanation for the slight improvement of the hearing capacity could be less ototraumatic influence of AOM. Data about the occurrence of four common epidemic diseases, covering the periods preceding and succeeding the years when the participants were born indicated that influenza and possibly pertussis (whooping cough), constitute putative prenatal risk factors for mild to moderate high frequency hearing loss.