Epidemiology of early-onset bloodstream infection and implications for treatment

HEALTH CARE-ASSOCIATED INFECTIONS: For over 35 years, infections have been divided into hospital acquired or community acquired. In 2002, in a study of bloodstream infections (BSIs), Friedman et al first suggested creating a new classification: health care-associated BSIs. Kollef et al furthered the concept of health care-associated infection in a 2005 population-based study of culture-positive pneumonia cases. Although the site of infection differed, Kollef et al's results supported Friedman et al's original concept. Then in 2006, Kollef et al reported a population-based study focused specifically on BSIs. Of 6697 reported cases, 468 (7%) had hospital-acquired BSIs; 3705 (55.3%) health care-associated BSIs; and 2524 (37.7%) community-acquired BSIs. The clinical features of those with health care-associated BSIs differed from those with community-acquired BSIs. For several organisms, including Staphylococcus aureus, Streptococcus pneumoniae, and gram-negative organisms, the frequencies for health care-associated and hospital-acquired BSIs were similar to each other but significantly different from community-acquired BSIs. After controlling for several clinical features, methicillin-resistant Staphylococcus aureus had the largest odds ratio for predicting in-hospital mortality. Both hospital-acquired and health care-acquired cases were independent risk factors for in-hospital mortality.

Is more aggressive, empiric, gram-positive therapy warranted for this potentially sicker patient group? Wunderink pointed out the potential unintended consequences of such an approach and the paucity of good tools for early recognition of sickest patients. A study by Shorr et al of systemic inflammatory response syndrome, organ dysfunction, and mortality suggested that there may be approaches that could be used to stratify cases into high-risk groups who may benefit from more aggressive therapy. Most recently, Micek et al found that in health care-associated pneumonia cases, inappropriate initial empiric antibiotic treatment is an independent predictor of mortality. Treatment recommendations are evolving.

For pneumonia and BSIs, health care-associated infections appear to be distinct entities. However, operational definitions still vary. Compared with hospital-acquired cases, health care-associated cases have different clinical characteristics. The outcomes of health care-associated infections tend to be intermediate of the community-acquired and hospital-acquired groups. Further research is urgently needed on the implications of health care-associated infection for early therapy.