Incidence and relative risk for hepatitis A, hepatitis B and tuberculosis and occurrence of malaria among merchant seamen.

The purpose of the study was to assess the incidence and relative risk of hepatitis A and B and tuberculosis among Danish merchant seamen. We also assessed the occurrence of malaria. The study was based on record linkage of a research database containing data on 24,132 Danish male seamen and the Registry for Notifiable Infectious Diseases in Denmark, supplemented by data from other sources. The standardized incidence ratio (SIR) for hepatitis A for male seamen was 1.77 (0.91-3.10) as compared with the incidence in the general population. The incidence was 0.9 notified cases/10,000 years. The SIR for hepatitis B for male seamen was 3.02 (1.79-4.78), the main risk factors being intravenous drug use and casual sex abroad. Tuberculosis was not more common among seamen than in non-seamen. The results have implications for vaccination strategies in this occupational group. Malaria occurred frequently in the seamen, especially among those involved in West African trade. Irregular use of malaria prophylaxis and probably chloroquine resistance were of importance in some cases. To detect further cases of hepatitis A and B and malaria, other sources were reviewed. Only a few extra cases were identified. The registry of notifiable infectious diseases was thus found to be rather complete.