Toxic shock syndrome (TSS) is a very rare but potentially fatal illness caused by a bacterial toxin. Different bacterial toxins may cause toxic shock syndrome, depending on the situation. The causative bacteria include Staphylococcus aureus and Streptococcus pyogenes. Streptococcal TSS is sometimes referred to as toxic shock-like syndrome (TSLS) or Streptococcal Toxic Shock Syndrome (STSS).