Consensus of Infection Definition
Infection is a major problem in the intensive care unit (ICU), and infection is an integral part of sepsis. Almost any epidemiologic or intervention study that deals with infection or its consequences will need to include definitions of infection at various sites as part of its protocol.Although there are a number of published systems that suggest working definitions of infection that can be used, for instance for infection control purposes, there are no universally agreed upon definitions of infection as they apply to patients with severe sepsis or septic shock in the ICU. Some of the infections that occur in the ICU can easily be included within existing definitions. For instance, the use of the standard microbiological definition of a urinary tract infection as 105 colonyforming units (cfu)/mL of pure growth of an organism is not unreasonable for a noncatheterized ICU patient. However, in many more common and more serious infections that are encountered in the ICU, these “standard” definitions are neither appropriate nor particularly helpful. The most obvious example is pneumonia, which presents particular problems.
It would greatly improve the quality and comparability of clinical trials of sepsis if there were a set of definitions for infection, customized for patients in the ICU, that could find widespread acceptance. Therefore, the International Sepsis Forum (ISF) convened an international consensus conference to formulate a set of definitions of infections that occur commonly in the ICU. The purpose of these proposed definitions is to determine whether the infection is likely to be present in patients who have the clinical syndrome of severe sepsis or septic shock. The definitions have been developed specifically for use in clinical studies of sepsis and thus are intended to maximize specificity and minimize false positives. It is recognized that in clinical practice, a different definition might be used to de- fine who should receive antibiotic therapy, but this type of more sensitive definition will have more false positives.
METHODS
A panel of international experts in the fields of intensive care medicine, infectious diseases, and clinical microbiology, all of whom had a particular interest in sepsis, were invited to participate in a 2-day consensus conference held in Coral Gables, FL (November 8 and 9, 2003). The ISF provided logistic support for the meeting, but not all of the panelists were members of the ISF.
Before the panel convened, the joint chairs (JC and TC) used published epidemiologic databases to identify the six most common sites of infection that occurred in the ICU. (Although other sites, such as central nervous system infections, do sometimes give rise to shock, they are rare and it was agreed not to include them.) Each of the chosen sites was then allocated to two members of the panel who would act as rapporteurs for the group. For each infection site, the rapporteurs were asked to carry out a literature review and to seek expert advice and opinion to provide a draft definition. The remit from the co-chairs was to develop a definition that was based on published evidence, insofar as that was possible, and that was suitable for use as part of a clinical trial in septic patients. It was important that the definition was practicable and did not require specialist or unusual equipment (e.g., a definition based on a polymerase chain reaction method would be unsuitable). General clinical features of infection (e.g., fever, tachycardia, etc., as used in the current consensus definitions of sepsis and septic shock) were regarded as a given and did not need to be reiterated for each site. The draft definitions drawn up by the rapporteurs were circulated to the entire group before the consensus conference.
Rapporteurs presented the draft definitions to the conference, and these were refined and improved during discussion. Modifications were circulated electronically and subsequently agreed upon as part of an iterative process over a period of approximately 7 months until consensus was reached.
RESULTS
The six most common infection sites were identified as pneumonia, bloodstream infections (including infective endocarditis), intravascular catheter-related sepsis, intra-abdominal infections, urosepsis, and surgical wound infections. In the following sections we provide a brief rationale and background and the suggested formulation of each definition.
Pneumonia
For the purposes of defining whether pneumonia is present or absent, it is not necessary to make the distinction between community-acquired pneumonia (CAP), health care-related pneumonia, hospital-acquired pneumonia, and ventilator- associated pneumonia (VAP), although their associated risk factors and presentations differ.
Controversy continues about how to best diagnose VAP, but specificity is improved only after microbiological culture data are obtained, information that is seldom available when patients are first evaluated for the etiology of sepsis symptoms. Therefore, the definition is designed to maximize the likelihood of the patient having respiratory infection, using clinical criteria, but the initial diagnosis of pneumonia can be modified once microbiological data become available.
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