CHICKEN-POX is on the increase among adults, who now account for about half of all cases, according to the latest figures published in Mims. Among the over-14s last year it peaked at about 300 per 100,000, compared with 68 per 100,000 in the years before 1975. While the disease is usually mild in childhood, it can be severe in adults and can cause pneumonia. There has also been a rise in the disease during pregnancy, when chicken-pox can affect the foetus.