Key Point

Less severely ill patients are at greater risk of dying from a bloodstream infection than more severely ill patients. This has important implications for infection control outside the ICU.

BALTIMORE—The incidence of mortality after bloodstream infections in the ICU is between 35% to 60% but can range from 5% to 80%. Because of the severity of illness in ICU patients, it is often difficult to distinguish mortality due to bloodstream infection from mortality due to underlying causes.

A group of researchers from the CDC- funded Prevention Epicenter based at Johns Hopkins medical institutions recently conducted a prospective cohort study in patients from five ICUs in three tertiary care centers in Baltimore. They found that patients who were less severely ill had a risk of mortality from bloodstream infections nearly twice as high as that in more severely ill patients.¹

The study included 2,783 adult ICU patients. Of these, 269 developed bloodstream infections more than 48 hours after admission to the ICU. These were classified as primary or secondary infections according to CDC National Nosocomial Infection Surveillance System definitions. APACHE II scores were calculated for all patients within the first 24 hours of admission to the ICU.

Sixty-eight percent of patients had primary bloodstream infections, and 95% of these had a central line in place at the time their bloodstream infections were diagnosed. The major infection-causing pathogens—in order of frequency—were Enterococcus species, coagulase-negative staphylococci, gram-negative organisms, Candida species, and Staphylococcus aureus.

MORTALITY LINKED TO APACHE SCORE

Patients with bloodstream infections were three times more likely to die during their hospital stay than patients without such infections. They were also more severely ill according to their APACHE II scores. When patients were stratified by their APACHE scores, those with a score of less than 20 had 2.42 times the risk of death in hospital compared with those who did not have bloodstream infections and had low APACHE scores. Interestingly, those whose APACHE scores were 20 or higher did not have an increased risk of in-hospital mortality. As expected, virulence of the infecting organisms was associated with a sevenfold increased risk of in-hospital death among patients with low APACHE scores. However, in patients with a high APACHE score, virulence of the infecting organisms increased mortality risk by only 1.93 times.

“We found that a less ill patient who got an infection had twice the risk of dying as a similarly less ill patient who didn’t get an infection. In contrast, the more ill patients who got an infection had about the same risk of dying as the more ill patient who didn’t get an infection,” said Mary-Claire Roghmann, MD, MS, Hospital Epidemiologist at the VA Maryland Health Care System. “We did not expect to find this difference,” she added. “However, our findings are biologically plausible. Patients with higher severity of illness may have many reasons for increased mortality. The addition of a bloodstream infection to these patients’ list of life-threatening problems may be inconsequential.”

The study is the largest cohort study to assess the relation between mortality and bloodstream infections in the ICU, noted the authors. Their findings support the prevention of bloodstream infections in less severely ill patients as well as at-risk patients in medical or surgical wards.

“Infections that occur during a hospitalization for another medical illness are a major patient safety problem,” explained Dr. Roghmann, who is also an Associate Professor of Epidemiology and Preventive Medicine at the University of Maryland School of Medicine in Baltimore. “These infections are more common in the sickest patients, and thus, hospitals often provide more infection prevention in these patients. Our study suggests that this strategy may not be the best one. Clearly, we want our infection prevention efforts to have the biggest impact possible on our patients’ safety,” she stressed. “To do this, we may need to provide more infection prevention in our less ill patients.”

—Gale Jurasek

Reference
1. Kim PW, Perl TM, Keelaghan EF, et al. Risk of mortality with a bloodstream infection is higher in the less severely ill at admission. Am J Respir Crit Care Med. 2005;171:616-620.

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