A progressive state of systemic inflammation characterized by a white blood cell count greater than 12,000/mm3 or less than 4000/mm3, temperature greater than 38°C or less than 36°C, tachycardia, tachypnea, and decreased blood carbon dioxide levels. SIRS can begin with any serious illness or injury involving inflammation but is most often associated with systemic infection (sepsis) caused by gram-negative bacteria.