The prevalence of varicella-zoster virus infection in normal healthy individuals aged above 6 months.

The prevalence of varicella-zoster virus (VZV) infection was studied by determining the presence of IgG antibody to VZV (anti-VZV IgG) using ELISA method. Three hundred and fifty sera collected from Thai healthy individuals aged above 6 months (mean age +/- standard deviation = 14.9 +/- 11.4) were tested, the prevalence of VZV infection was 64.6% (225/350). All samples were randomly sampling from healthy children and blood donors who visited the hospital and clssified into 7 groups, 50 samples each, according to their age, i.e., group 1; 6 months-3 years, group 2; 4-6 years, group 3; 7-9 years, group 4; 10-14 years, group 5; 15-19 years, group 6; 20-24 years and group 7; above 25 years. The prevalence of VZV infection were 12%, 42%, 64%, 70%, 78%, 84% and 100% respectively. The mean amount of anti-VZV IgG among groups of positive VZV infection (225 samples) was 86.8 +/- 29.7 unit/ml. The mean amount of anti-VZV IgG was highest in 6 months-3 years age group (113.6 +/- 39.2 unit/ml). Significant difference of the mean amount of anti- VZV IgG was found between group 1, 3, 6 and other groups (p-value < 0.05). There was a correlation between history of varicella and the presence of anti-VZV IgG in the serum. 95.3% of individuals with positive history has already had the antibody. The important associated factors that might involve VZV infection were age, number of members in family and place of exposure to VZV infection. Other factors, such as sex and income did not show any association to VZV infection.