Until 2008, a distinction was made between two types: complicated SSSIs (cSSSIs) and uncomplicated SSSIs (uSSSIs),[3] which had different regulatory approval requirements.[4][needs update] Uncomplicated SSSIs included "simple abscesses, impetiginous lesions, furuncles, and cellulitis."[4] Complicated SSSIs included "infections either involving deeper soft tissue or requiring significant surgical intervention, such as infected ulcers, burns, and major abscesses or a significant underlying disease state that complicates the response to treatment."[4] The FDA further noted that "[s]uperficial infections or abscesses in an anatomical site, such as the rectal area, where the risk of anaerobic or Gram-negative pathogen involvement is higher, [were also] considered complicated infections."[4] The uncomplicated category (uSSSI) is most frequently caused by Staphylococcus aureus and Streptococcus pyogenes, whereas the complicated category (cSSSI) might also be caused by a number of other pathogens.[4][verification needed] As of 2013, the pathogen involved in cases of cSSSI were known about 40% of the time.[4][needs update][verification needed]