Key Point

Patient characteristics—specifically sex and age—may be predictors of bloodstream infection type and incidence.

Primary bloodstream infection (BSI)—defined by the CDC as infection that is microbiologically documented (as opposed to clinical sepsis, which is not)—is a leading complication in critically ill patients. Despite modern advances in antimicrobial therapy, mortality rates among patients with BSI can climb as high as 20% to 30%, research shows. Therefore, to help target treatment and prevention efforts, Daniel Z. Uslan, MD, from the Mayo Clinic College of Medicine in Rochester, Minnesota, and colleagues conducted a retrospective, population-based cohort study to evaluate age- and sex-associated trends in BSI. Among other things, they found that the distribution of organisms in patients with BSI varies significantly according to patients’ age and sex, reported the investigators in an article published in the April 23 Archives of Internal Medicine.

Using a computerized database, the researchers identified cases of nosocomial, health care–associated, or community-acquired BSI in Olmstead County, Minnesota, that occurred from January 2003 to December 2005. With these records, the authors calculated incidence rates. Data for 650 patients with positive blood cultures were included in the analysis.

The mean age of patients was 63; about 52% were men, 10% were nonwhite, and 29% were older than 80.

Escherichia coli (25%) and Staphylococcus aureus (17%) were the most common causative organisms. Nosocomial, health care–associated, and community-acquired BSI accounted for 19.1%, 36.5%, and 44.5% of cases, respectively. Men were much more likely than women to have nosocomial infections, with a distribution of 23.8% versus 13.9%.

The overall incidence rate of BSI was 237 per 100,000 person-years for men and 156 for women. While incidence rates increased with age for both sexes (474.6 per 100,000 person-years in the 60-to-79 age-group vs 140.6 in the 40-to-59 age group), incidence rates for men were substantially higher than those for women in the “over 70” group. For men older than 80, the incidence rate was 2,149.1 per 100,000 person-years; for women, 1,143.7.

Women were significantly more likely than men to have E coli infections (incidence rate, 61 vs 32 per 100,000 person-years, respectively), which probably reflects women’s propensity for urinary tract infections, the authors suggested. More women than men had infections due to gram-negative bacilli (85 vs 79). Infections that were more common in men than in women were S aureus (incidence rates, 46 vs 23 per 100,000 persons, respectively) and viridans group streptococci infection (16 vs 5 per 100,000 person-years). Also more common in men than in women were infections due to gram-positive cocci (133 vs 64 per 100,000 person-years), which may be “directly related to the increased number of nosocomial BSIs in males,” the authors speculated.

“[S]ex-specific BSI trends may have implications for empirical antimicrobial therapy in patients with presumed BSI, especially as rates of antimicrobial resistance increase,” Dr. Uslan and colleagues noted. “Further research on specific sex-associated risk factors for BSI is needed to clarify these trends,” they concluded.            

—Adriene Marshall

Reference
Hugonnet S, Sax H, Eggimann P, et al. Nosocomial bloodstream infection and clinical sepsis. Emerg Infect Dis. 2004;10:76-81.
Uslan DZ, Crane SJ, Steckelberg JM, et al. Age- and sex-associated trends in bloodstream infection: a population-based study in Olmsted County, Minnesota. Arch Intern Med. 2007;167:834-839.

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