Classifying Types of Bacterial Infections

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The summary below is from the full report titled "Health Care–Associated Bloodstream Infections in Adults: A Reason To Change the Accepted Definition of Community-Acquired Infections." It is in the 19 November 2002 issue of Annals of Internal Medicine (volume 137, pages 791-797). The authors are ND Friedman, KS Kaye, JE Stout, SA McGarry, SL Trivette, JP Briggs, W Lamm, C Clark, J MacFarquhar, AL Walton, LB Reller, and DJ Sexton.

What is the problem and what is known about it so far?

Bacteria entering the blood can cause serious problems called bloodstream infections (bacteremia). In the past, doctors classified bloodstream infections as community-acquired or nosocomial. Community-acquired infections occurred in otherwise relatively healthy outpatients. Nosocomial infections occurred in very sick hospitalized patients. Doctors chose antibiotic drugs on the basis of the two kinds of infections because different types of bacteria typically caused them. In the past decade, sicker patients with complicated illnesses such as cancer and kidney failure requiring dialysis are routinely cared for in outpatient settings. Bacteremia in these sicker outpatients may be more like nosocomial infections than like community-acquired infections.

Why did the researchers do this particular study?

To develop a more useful classification system for bloodstream infections.

Who was studied?

504 adults with symptoms or signs of infection and positive blood cultures.

How was the study done?

The researchers reviewed blood culture reports of hospitalized patients from one academic medical center and two community hospitals in North Carolina. They then reviewed medical records of patients with positive blood cultures to learn about symptoms, signs, and sites of infection and medical conditions and treatments. They placed the patients into one of three groups (community-acquired, health care–associated, and nosocomial) and compared infection and patient characteristics across groups. The nosocomial group first had positive blood cultures at least 48 hours after hospitalization for another problem. The health care–associated group had positive blood cultures at the time of or within 48 hours of hospitalization and had recently needed complicated care (nursing home and dialysis patients, patients recently hospitalized, and patients recently given medicine in a vein [intravenous] at home). The community-acquired group first had positive blood cultures at the time of or within 48 hours of hospitalization but did not fit criteria for a health care–associated infection.

What did the researchers find?

Patients with community-acquired infections less often had cancer than patients in the other groups. The most common source of bloodstream infection differed by group: urinary tract infections in the community-acquired group and tubes inserted in veins to give treatment in the other groups. Two bacteria (Escherichia coli and Streptococcus pneumoniae) frequently caused community-acquired infections. Staphylococcus aureus frequently caused health care–associated and nosocomial infections. Bacteria resistant to antibiotics were infrequent with community-acquired infections. More patients with nosocomial infections (37%) died than patients with health care–associated (29%) and community-acquired (16%) infections.

What were the limitations of the study?

The study was from one area in North Carolina. Patterns of health care and infections may vary in different areas. The definition of health care–associated infection was broad and included patients with different risks for infection.

What are the implications of the study?

Health care–associated bloodstream infections acquired in the outpatient setting are different from community-acquired bloodstream infections in relatively healthy people.