Secondary attack rate of chicken pox is

Chicken pox Agent- Human alpha herpes virus 3 Primary infection causes chicken pox Recovery from primary infection is commonly followed by establishment of latent infection in cranial nerves, sensory ganglia, spinal dorsal root ganglia When the cell mediated immunity wanes, the virus may reactivate in 10-30% cases Incubation period -15 days Distribution of rash:- Centripetal; Axilla affected; Rash seen mostly over flexor aspect Characteristics of rash:- Superficial; Unilocular-dew drops like appearance Rash pleomorphic- different stages of rash evident at one time An area of inflammation seen around vesicle Evolution of rash : very rapid Scab begins to form 4-7 days after the rash appears Fever- temperature rises with each fresh crop of rash Secondary attack rate-90% Reference: Park&;s textbook of Preventive and Social medicine, 23rd edition; Page no.144