Strep throat is caused by group A β-hemolytic Streptococcus (GAS or S. pyogenes). Other bacteria such as non–group A β-hemolytic streptococci and fusobacterium 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".