Strep throat is a bacterial infection of the throat. The infection is caused by Sreptococcus (Group A Beta Hemolytic Strep) bacteria. It is transmitted through the saliva and/or nasal secretions. Streptococcus bacteria takes 2-5 days to incubate in the upper respiratory tract and people with strep throat remain contagious for 1-3 days after antibiotics are started. Children may return to school 24 hours after starting antibiotics.