Researchers Suggest Adding New Classification for Bloodstream Infections

DURHAM, NC -- Hospitals and disease surveillance agencies should consider adding a third category -- 'health care-associated infections' -- to the system currently used to classify bloodstream infections in patients, according to Duke University Medical Center researchers.

The proposed new category would describe those infections originating in non-hospital medical settings, such as nursing homes, outpatient dialysis and chemotherapy clinics and home health services. The researchers say adding this new category would help guide diagnostic and treatment decisions. The two current infection categories are 'hospital-acquired' and 'community-acquired.'

The Duke researchers report their findings and recommendations in today's (Nov. 19, 2002) issue of the Annals of Internal Medicine.

'Currently, we only classify infections as hospital-acquired and community-acquired,' said Deborah Friedman, M.B.B.S., currently an infectious diseases physician at Victorian Infection Control Nosocomial Infection Surveillance System in Melbourne, Australia, and lead author of the study. The study was completed while Friedman was a fellow in infectious diseases at Duke University Medical Center.

'However, with the wide variety of outpatient medical services currently available, there is the potential for patients receiving outpatient care to develop infections that were historically associated exclusively with a hospital stay,' said Friedman. 'The irony is that we still classify those infections as community-acquired, even though they may well have originated in a medical setting.'

The Duke team studied 504 patients with bloodstream infections detected by blood cultures at three hospitals (including one tertiary care center and two community hospitals). Each infection was classified as either:

• hospital-acquired (nosocomial) -- an infection detected after the patient had been hospitalized for 48 hours or more
• community-acquired -- an infection diagnosed upon hospital admission or within 48 hours of admission in patients who had not had significant recent contact with the health care system; or
• health care-associated -- diagnosed upon admission to the hospital, or within 48 hours of hospital admission, in patients who had recent contact with the health care system in the form of home health care, outpatient intravenous therapy (for example, chemotherapy or dialysis), nursing homes or recent hospitalization.

This study was funded by an educational grant from Merck Pharmaceuticals.

The Duke researchers found that of the 504 patients studied, 175 had hospital-acquired infections, 143 had community-acquired infections and 186 suffered health care-associated infections. Moreover, Staphylococcus aureus (S. aureus) represented the most common cause of hospital-acquired and health care-associated infections, while community-acquired infections were more commonly associated with Escherichia coli (E. coli) and Streptococcus pneumoniae.

'The primary advantage of having the health care-associated category is that it would assist physicians in providing swift and accurate diagnosis and treatment of infections,' said Daniel Sexton, M.D., professor of medicine at Duke University Medical Center and senior author of the study.

Standard antibiotics are often effective in the treatment of community-acquired infections. However, hospital-acquired and health care-associated infections are similar in that they often require more sophisticated treatments because the infections are often resistant to standard antibiotics, said the researchers.

Hospital-acquired infections are considered the most difficult infections to treat, said the researchers. Because they occur only after a patient has been hospitalized for another medical condition, treatment has to be considered in light of patients' existing medical problems. Hospital-acquired infections are also more likely to be resistant to antibiotics than are community-acquired infections, said the researchers.

'For example, methicillin-resistant Staphylococcus aureus (MRSA) is an infection that has historically been associated almost exclusively with hospital settings,' said Sexton.

MRSA are strains of S. aureus that do not respond to treatment with the standard and preferred choice of antibiotics.

The Duke researchers found that MRSA occurred with similar frequency in patients with hospital-acquired infections (61 percent) and health care-associated infections (52 percent), but was uncommon in patients with community-acquired infections (14 percent).

'This finding underscores our hypothesis that more serious infections are being spread in non-hospital settings than physicians are traditionally trained to expect,' said Keith Kaye, M.D., assistant professor of medicine at Duke University Medical Center and a study co-author.

Differentiating between community-acquired and health care-associated infections would aid physicians' decision-making process when evaluating treatment options for patients who appear not to have been infected during a hospital stay, said the researchers.

'The current practice is to use standard antibiotics for community-acquired infections, and more sophisticated treatments for hospital-acquired infections that are more likely to be antibiotic resistant,' said Kaye. 'However, this study shows that a high percentage of patients with health care-associated infections also have resistant infections, and that we would be wise to approach treatment of these infections in a similar manner as we now treat hospital-acquired infections.'

'Essentially, modern medical science has resulted in shorter hospital stays for many conditions,' said Friedman. 'Any number of medical conditions can now be managed on an outpatient basis, which is an advantage for patient quality-of-life. However, it means that there are more people with weakened immune systems living in general society and receiving outpatient or nursing home care. Our current infection control system does not account for the fact that these patients are being exposed to and are susceptible to infectious agents that are generally associated with a hospital setting.'

Adding the health care-associated category of infection would also have implications for infection control surveillance practices, said Friedman.

'Currently, most infection control programs only monitor rates of infections within hospitals and hospital-affiliated clinics, said Kaye. 'Including health care-associated infections in surveillance would result in more extensive tracking of infection rates and sources in outpatient clinics and nursing homes, which in turn would provide more opportunities for intervention and prevention of the spread of infections'

Joining Friedman, Sexton and Kaye on this study were Jason Stout, M.D., Sarah McGarry, M.D., Sharon Trivette, Jane Briggs, Wanda Lamm, Connie Clark, Jennifer MacFarquhar, Aaron Walton, M.D. and L. Barth Reller, M.D., all of Duke University Medical Center.