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A total of 593 inhabitants of Graciosa Bay, Santa Cruz, the Solomon Islands were tested for HBsAg and anti-HBs in 1974 and again in 1977. An additional 102 children born during this study period were tested for HBsAg and anti-HBs in 1977. Loss of HBsAg was observed in 20% of the 66 HBsAg-positive individuals identified in 1974 and retested in 1977. Conversely, acquisition of HBV infection, as documented by seroconversion on HBsAg or anti-HBs, was observed in 38% of the individuals identified as negative for all HBV markers in 1974. Acquisition of HBsAg was noted in 22 individuals, eight of whom were born after 1974. Acquisition of HBsAg was noted in 66 individuals, two of whom were born after 1974. Males and females acquired HBV infection at somewhat similar rates (42% vs. 34%), except between ages 15 and 29 years, when males were infected at a much higher rate (53%) than females (11%) (p = 0.008). Contact with a carrier appears to be the predominant mode of transmission of the virus. Acquisition of HBV by children and females was strongly correlated with the presence of an HBsAg-positive individual among the household contacts. Adult males, on the other hand, tended to acquire HBV infections from sources outside their family or household setting. The relationship between the patterns of acquisition of HBV infection and the cultural practices in this Melanesian population is discussed.

The population of Graciosa Bay, Santa Cruz, British Solomon Islands Protectorate, was tested for HBsAg and anti-HBs in 1973 and 1974. Both the antigen and antibody occurred more often in males, presumably due to a higher exposure rate. None of 28 infants under one year of age had antigen and only one of 50 individuals under two years (2%) did. The prevalence of antigenemia was higher in older children and did not decline with increasing age. This pattern is contrasted to that found in other populations which is characterized by onset during the first year and a decrease in prevalence in older age groups. The ratio of antigenemia prevalence to that of antibody is significantly higher in the population under six years of age (p less than 0.01), indicating that younger infected people tend to be asymptomatic carriers while older individuals tend to have produced antibody. Three of 28 individuals with antigen detectable by immunodiffusion in 1973 had lower levels, detectable only by reversed passive hemagglutination after one year. The age specific prevalence of anti-HBs increases to a peak of 34% in the 15-19 year age group and declines thereafter.

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