. 2022 Dec 20;23:1029. doi: 10.1186/s13063-022-06975-6

Table 1.

Definition and classification of surgical site infection (adapted from CDC) [6]

	Infection occurs within 30 days after the operation …
Superficial incisional SSI (class I)	…and infection involves only skin or subcutaneous tissue and at least *one* of the following: 1 Purulent drainage from the superficial incision 2 Organisms isolated from an aseptically obtained culture of fluid or tissue from the superficial incision. 3 At least one of the following signs or symptoms of infection: pain or tenderness, localized swelling, redness, or heat and superficial incision is deliberately opened by surgeon, unless incision is culture negative.
Deep incisional SSI (class II)	…and infection involves deep soft tissues (fascial and muscle layers) and at least one of the following: 1 Purulent drainage from the deep incision but not from the organ/space component of the surgical site. 2 A deep incision spontaneously dehisces or is deliberately opened by a surgeon 3 And at least one of the following symptoms: fever (>38°C), localized pain, or tenderness of the incision area unless incision is culture negative. 4 An abscess or other evidence of infection involving the deep incision is found on direct examination, during reoperation, or by histopathologic or radiologic examination.
Organ/space SSI (class III)	…and infection involves any part of the anatomy (e.g. organs or spaces), other than the incision, which was opened or manipulated during an operation and at least one of the following: 1 Purulent drainage from a drain that is placed through a stab wound into the organ/space. 2 Organisms isolated from an aseptically obtained culture of fluid or tissue in the organ/space. 3 An abscess or other evidence of infection involving the organ/space that is found on direct examination, during reoperation, or by histopathologic or radiologic examination.
	…or the infection is diagnosed by the attending surgeon

Infection occurs within 30 days after the operation …

Superficial incisional SSI

(class I)

…and infection involves only skin or subcutaneous tissue

and at least one of the following:

1 Purulent drainage from the superficial incision

2 Organisms isolated from an aseptically obtained culture of fluid or tissue from the superficial incision.

3 At least one of the following signs or symptoms of infection: pain or tenderness, localized swelling, redness, or heat and superficial incision is deliberately opened by surgeon, unless incision is culture negative.

Deep incisional SSI

(class II)

…and infection involves deep soft tissues (fascial and muscle layers)

and at least one of the following:

1 Purulent drainage from the deep incision but not from the organ/space component of the surgical site.

2 A deep incision spontaneously dehisces or is deliberately opened by a surgeon

3 And at least one of the following symptoms: fever (>38°C), localized pain, or tenderness of the incision area unless incision is culture negative.

4 An abscess or other evidence of infection involving the deep incision is found on direct examination, during reoperation, or by histopathologic or radiologic examination.

Organ/space SSI

(class III)

…and infection involves any part of the anatomy (e.g. organs or spaces), other than the incision, which was opened or manipulated during an operation and at least one of the following:

1 Purulent drainage from a drain that is placed through a stab wound into the organ/space.

2 Organisms isolated from an aseptically obtained culture of fluid or tissue in the organ/space.

3 An abscess or other evidence of infection involving the organ/space that is found on direct examination, during reoperation, or by histopathologic or radiologic examination.

…or the infection is diagnosed by the attending surgeon