HEPATITIS A VIRUS INFECTION IN HOUSEHOLDS

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Abstract
The behavior of hepatitis A virus (HAV) infection among 980 members of 230 famiiies in two rural districts of Costa Rica was studied prospectively from the recognition of the index case. The Initial prevalence of detectable antibody (anti-HAV) ranged from 26.2% in chiidren to 71.4% in adults. The ratio of index to household-associated infections was significantly higher among children than among adolescents and adults, indicating that chiidren were most often responsible for the HAY introduction. The rates of household-associated cases among susceptible contacts were 70-83%; the finai prevaiences of anti-HAV were 90–95%. Neither index showed significant diflerences reiated to age. The ratio of cilnical to silent infections in househoid-assoclated cases was uniformly 1.8:1 among chiidren and adoiescents; among aduits, almost all associated infections were silent. Beginning with the 5–9-year age group, however, an immunoglobulin M response was absent in a progressively larger proportion of inapparent infections, strongly suggesting restimulation of specific immunoglobulin G antibodies by reinfection.