<P> Hemorrhagic complications are more common in the immunocompromised or immunosuppressed populations, although healthy children and adults have been affected . Five major clinical syndromes have been described: febrile purpura, malignant chickenpox with purpura, postinfectious purpura, purpura fulminans, and anaphylactoid purpura . These syndromes have variable courses, with febrile purpura being the most benign of the syndromes and having an uncomplicated outcome . In contrast, malignant chickenpox with purpura is a grave clinical condition that has a mortality rate of greater than 70% . The cause of these hemorrhagic chickenpox syndromes is not known . </P> <P> Primary varicella occurs in all countries worldwide . In 2013 the disease resulted in 7,000 deaths--down from 8,900 in 1990 . </P> <P> In temperate countries, chickenpox is primarily a disease of children, with most cases occurring during the winter and spring, most likely due to school contact . It is one of the classic diseases of childhood, with the highest prevalence in the 4--10 - year - old age group . Like rubella, it is uncommon in preschool children . Varicella is highly communicable, with an infection rate of 90% in close contacts . In temperate countries, most people become infected before adulthood, and 10% of young adults remain susceptible . </P> <P> In the tropics, chickenpox often occurs in older people and may cause more serious disease . In adults, the pock marks are darker and the scars more prominent than in children . </P>

Why is chicken pox more common in spring