ATLANTA--An estimated 875,000 to 3.5 million nosocomial infections occur among American inpatients each year, and 10% of these involve the bloodstream. Mortality directly attributable to nosocomial bloodstream infections is 10% to 30%.

On the basis of these figures, nosocomial bloodstream infection is rated at anywhere from the fourth to the 13th leading cause of death in the United States, stated Richard Wenzel, MD, chairman and professor of medicine at the Medical College of Virginia Commonwealth University in Richmond. That places it in the company of such well-known killers as pneumonia, influenza, and stroke.

However, nosocomial bloodstream infections are preventable, said Dr. Wenzel, who spoke recently at the 4th Decennial International Conference on Nosocomial and Healthcare-Associated Infections. And prevention could reduce the tremendous number of years of life lost due to these infections--which, by conservative estimates, reaches tens of thousands annually.

MORTALITY RISK FACTORS

"The number one cause of nosocomial bloodstream infection is coagulase-negative Staphylococcus, and this infection has a crude mortality rate of 21%," Dr. Wenzel recently told PULMONARY REVIEWS. The number two, three, and four causes are Staphylococcus aureus, Enterococcus, and Candida, which have crude mortality rates of 25%, 32%, and 40%, respectively.[1]

Inappropriate antibiotic therapy is a major risk factor for death from nosocomial bloodstream infection. Mortality is as high as 77%, for example, when very severe, rapidly fatal cases are treated with antibiotics to which they are resistant, versus only about 29% when the correct antibiotic is chosen. Mortality also drops with appropriate antibiotic therapy for less severe cases. "You need to know your antibiogram (the list of pathogens common in your institution and the corresponding effective antibiotics)," commented Dr. Wenzel. "The nurses know it. Listen to them."

Hypothermia is another important risk factor for death in patients with nosocomial bloodstream infection. In one study, 70% of hypothermic patients died, versus 38% of febrile patients.[2] Other independent predictors of death included the presence of Candida albicans, Pseudomonas aeruginosa, and secondary or polymicrobial infection.

The level of staff training is crucial. One study has shown that mortality associated with septic shock is markedly higher on general hospital wards than in the intensive care unit (ICU) (70% vs 38%, respectively).[3] This difference was found "despite the fact that the ICU patients were 10 years older and had an APACHE II score more than six points greater," Dr. Wenzel noted. Delays in administration of intravenous saline boluses (for reduced fluid volumes) and inotropic agents contributed to greater mortality rates in the general wards, he said.

Most recently, septic shock mortality was linked with the tumor necrosis factor (TNF)-alpha gene promoter polymorphism TNF2. The polymorphism was present more often in septic shock patients who died than in those who survived (52% vs 24%, respectively).[4] After adjustment for age and probability of death (as determined by Simplified Acute Physiologic Score [SAPS] II values), TNF2 was shown to multiply the mortality risk by 3.7 times among septic shock patients with similar SAPS II values.

Clinicians cannot alter the effect on mortality of Candida and other microbes, nor can they alter the patient's genetics or comorbidities, such as hypothermia, because these factors are part of the patient or environment. However, Dr. Wenzel stressed, "we can influence therapy if we're bright enough to pick the appropriate drug and smart enough to plan prospectively for an ICU team." But the real key to lowering mortality, he added, is prevention.

Because most nosocomial bloodstream infections are associated with central venous catheters, using catheters coated with antibiotics such as rifampin and doxycycline may be the best available preventive method. These devices can prevent 90% of central venous catheter--related bloodstream infections, research shows. Conservatively, this translates to between 5,000 and 9,500 lives saved per year, Dr. Wenzel estimated.

Handwashing with an alcohol-based disinfectant is only 10% to 20% as effective as using antibiotic-coated central venous catheters, he asserted, primarily because of poor compliance. However, it is far less expensive in terms of cost per life saved--about $10 versus more than $12,000 for antibiotic-coated catheter use. "But the two aren't mutually exclusive," Dr. Wenzel concluded. "We can do both."

--Timothy Begany

References
1. Edmond MB, Wallace SE, McClish DK, et al. Nosocomial bloodstream infections in United States hospitals: a three-year analysis. Clin Infect Dis. 1999;29:239-244.
2. Pittet D, Thievent B, Wenzel RP, et al. Bedside prediction of mortality from bacteremic sepsis. A dynamic analysis of ICU patients. Am J Respir Crit Care Med. 1996;153:684-693.
3. Lundberg JS, Perl TM, Wiblin T, et al. Septic shock: an analysis of outcomes for patients with onset on hospital wards versus intensive care units. Crit Care Med. 1998;26:1020-1024.
4. Mira JP, Cariou A, Grall F, et al. Association of TNF2, a TNF-alpha promoter polymorphism, with septic shock susceptibility and mortality: a multicenter study. JAMA. 1999;282:561-568.

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