 Strep throat is caused by group A beta @-@ hemolytic streptococcus ( GAS or S. pyogenes ) . Other bacteria such as non – group A beta @-@ hemolytic streptococci and <unk> may also cause pharyngitis . It is spread by direct , close contact with an infected person ; thus crowding , as may be found in the military and schools , increases the rate of transmission . Dried bacteria in dust are not infectious , although moist bacteria on toothbrushes or similar items can persist for up to fifteen days . Contaminated food can result in outbreaks , but this is rare . Of children with no signs or symptoms , 12 % carry GAS in their pharynx , and , after treatment , approximately 15 % of those remain positive , and are true " carriers " . 
