[Results of 29-year study of hoya (sea-squirt) asthma in Hatsukaichi, Hiroshima prefecture].

As remarkable improvements have been made to the working environment and working methods of oyster shucking workers during the past 30 years, a study was made on the effects of these improvements on hoya (sea-squirt) asthma and the following results were obtained. 1) The prevalence of hoya (sea-squirt) asthma among oyster shucking workers was 36.0%, 30.1%, 21.7%, 22.0%, 18.0%, and 26.6% in 1963, 1968, 1976, 1984, 1988, and 1992, respectively. Accompanying the improvements made to the working environment and working methods, asthmatic symptoms failed to develop in some of the patients through engaged in oyster shucking work. Thus, those with symptoms actually accounted for 36.0%, 18.7%, 15/8%, 7.4%, 8.4%, and 8.0% of the workers, respectively. 2) The proportion of serious cases among the patients rapidly decreased from 29.2% in 1963 to 0% after 1984. On the other hand the proportion of slight cases was 35.4% in 1963, but after 1988 all the cases were slight cases. 3) During the period from 1984 to 1992, the number of those newly engaged in oyster shucking work was 74. The number of those who developed hoya (sea-squirt) asthma during this period was 8 or 10.1%. All the cases were asthma of the rhinitis type. 4) The number of workers who did not develop asthmatic symptoms though engaged in oyster shucking work was 53 in 1984, 40 in 1988, and 49 in 1992. Of this number, 31% are now under hyposensitization therapy, 57.0% have received this therapy in the past, and 12.0% have not received any therapy.