RISK-FACTORS FOR INFECTION WITH AEROMONAS-SALMONICIDA SUBSP SALMONICIDA IN NORWEGIAN FRESH-WATER HATCHERIES

In 1991, a matched case-control study was performed in Norwegian fresh water hatcheries on risk factors for infection with Aeromonas salmonic ida subsp. salmonicida, the causative agent of furunculosis. The study was based on replies to a questionnaire mailed to smolt producers, an d included 30 infected and 66 non-infected hatcheries, matched by coun ty. The odds ratios for infection with A. salmonicida subsp. salmonici da in hatcheries associated with certain management and environmental factors were analyzed using a conditional logistic regression analysis . The study revealed that the main risk factors for infection with A. salmonicida subsp. salmonicida in freshwater hatcheries were: (1) migr ation of anadromous fish into the freshwater supply of the hatchery, ( 2) sharing of personnel with other fish farms, and (3) a high concentr ation of fish farms infected with A. salmonicida subsp. salmonicida ne ar the hatchery. Results indicate that the high prevalence of furuncul osis in Norwegian seawater farms has great impact on the risk of infec tion with A. salmonicida subsp. salmonicida in hatcheries, and also th at the bacterium may be transmitted between fish farms by humans.