Key Point

A panel of intensive care, infectious diseases, and microbiology experts has published definitions of the most common infections in patients with sepsis.

FALMER, UNITED KINGDOM—Since infection is ubiquitous in the ICU, it is surprising that there are no universally accepted definitions of infection in the setting of severe sepsis or septic shock. In an attempt to change this, a panel of international experts on intensive care, infectious diseases, and microbiology has published definitions of infection for the six most frequent causes of infection in septic patients.₁

The panel began collaborating in late 2003 at the two-day International Sepsis Forum Consensus Conference on Definitions of Infection in the Intensive Care Unit. There, the group refined and improved draft definitions of infection in the ICU that they had developed beforehand. Over the next seven months, they circulated and modified the definitions until consensus was reached.

The result of their collaborative effort? Definitions for infections in sepsis, including pneumonia, bloodstream infections, intravascular catheter-related sepsis, intra-abdominal infections, urosepsis, and surgical wound infections. “Although other sites, such as central nervous system infections, sometimes give rise to shock, they are rare and it was agreed not to include them,” wrote the authors.

PNEUMONIA

The panel agreed that pneumonia can be classified post hoc into one of three categories:

• Definite (microbiologically confirmed)—Clinically present with abnormal chest radiograph and the isolation of high concentrations of a likely or possible pulmonary pathogen from a quantitative lower respiratory tract sample or serological study.
• Probable—Clinically present with abnormal chest radiograph but no microbiological or serological evidence.
• Possible—Abnormal chest radiograph of uncertain cause with low or moderate clinical suspicion and microbiological or serological evidence.

BLOODSTREAM INFECTIONS

There are two criteria each for both primary and secondary bloodstream infections.

Primary:

• The presence of a recognized pathogen not usually regarded as a common skin contaminant in one or more blood cultures, or the presence of a common skin contaminant in two or more separately drawn blood cultures.
• The lack of a relationship between the cultured organism and the same infection at another site, including the site of an intravascular access device.

Secondary:

• The presence of a recognized pathogen not usually regarded as a common skin contaminant in one or more blood cultures.
• The cultured organism is related to the same infection at another site.

CATHETER-RELATED SEPSIS

Catheter-related sepsis is considered definite when there is at least one positive peripheral blood culture and one of the following findings:

• A positive semiquantitative or quantitative catheter-tip culture that grows the microorganism found in the peripheral blood.
• A positive hub or exit site culture that grows the same microorganism found in the peripheral blood.
• Positive paired central and peripheral blood cultures that grow the same microorganism; the former blood culture is positive at least two hours earlier or shows five times the growth.

  INTRA-ABDOMINAL INFECTIONS, UROSEPSIS, AND SKIN/SOFT-TISSUE INFECTIONS

  Like pneumonia, intra-abdominal infections are categorized as definite, probable, or possible. “Cultures from drain sites are not considered diagnostic of intra-abdominal infection,” the authors noted.

  Less virulent organisms such as coagulase-negative staphylococci and Bacillus species should be considered causes of intra-abdominal infection only when they have been isolated from intra-abdominal sources in pure culture. They should also be present in significant quantities—greater than 10⁵ colony-forming units (CFU)/mL, two times or greater on direct culture plating, or moderate to many on primary culture plating.

  “Blood cultures with microbial pathogens compatible with intra-abdominal infection will also be considered microbiologically confirmed infection in the presence of clinical signs and symptoms indicative of an intra-abdominal infection,” said the authors. They provided detailed definitions for nine such infections, including primary, secondary, and tertiary peritonitis, peritonitis related to peritoneal dialysis, intra-abdominal abscess, biliary tract infection, pancreatic infection, typhlitis, and toxic megacolon.

  Definitions were given for three types of urosepsis (sepsis due to urinary tract infection): urosepsis in catheterized patients and in noncatheterized patients and candiduria. In noncatheterized patients, the criterion for a urinary tract infection of more than 10⁵ CFU/mL of pathogen has gained wide acceptance. For catheterized patients, the authors used a threshold of 10³ CFU/mL because the pathogen level in these patients will quickly rise to 10⁵ CFU/mL if the infection is not treated with antibiotics.

  “For the sake of simplicity, skin and soft-tissue infections can be subdivided into surgical and nonsurgical infections,” said the authors. “Surgical site infection is an infection that arises within 30 days of an operative procedure and at the site of surgical intervention.”

  Two principal nonsurgical site infections were defined: cellulitis and necrotizing cellulitis and fasciitis; however, erysipelas, impetigo, folliculitis, pyodermas, and abscess are other examples of nonsurgical site infections.

  The authors expressed the hope that these definitions will be helpful in identifying populations for whom specific treatments are indicated, adding, “A further benefit would be the potential to provide a framework for guiding diagnostic or even therapeutic decision making in the ICU.”

  —Timothy Begany

  Reference
  1. Calandra T, Cohen J. The International Sepsis Forum consensus conference on definitions of infection in the intensive care unit. Crit Care Med. 2005;33:1538-1548.

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