The changing epidemiology of severe infections in the ICU

Abstract

Data on the epidemiology of severe infection in the intensive care unit (ICU) can be used to monitor the effect of preventive measures and changes in policy or procedures. The most common risk factors associated with ICU-acquired infection include length of stay, antibiotic usage, catheterization and use of other invasive devices. The most frequent infections encountered in ICU patients include lower respiratory tract infections (especially pneumonia) and bacteremia, in addition to urinary tract infections and wound infections. Streptococcus pneumoniae, Haemophilus influenzae, methicillin-susceptible Staphylococcus aureus and Enterobacteriaceae are most often implicated in community-acquired and early onset ICU-acquired infections, whereas late onset infection is more likely to be caused by pathogens which are more refractory to treatment, such as Enterobacter spp., Serratia spp., Pseudomonas aeruginosa, Acinetobacter spp. and methicillin-resistant S. aureus (MRSA). The pathogen spectrum also varies according to the site of infection, with Gram-positive bacteria being most frequently isolated in bacteremia and wound infections, whereas Gram-negative bacteria are prevalent in late-onset pneumonia and urinary tract infections. The prevalence of Gram-positive pathogens in bacteremia has increased over the past 20 years, mainly because of the increased isolation of coagulase-negative staphylococci (CNS) and enterococci. This is most probably due to the selective pressure exerted by the use of broad-spectrum antibiotics, such as the third-generation cephalosporins and fluoroquinolones, which are generally more potent against Gram-negative than Gram-positive bacteria, and to the increased use of invasive devices. The increasing isolation frequency of Gram-positive pathogens in severe ICU infections has resulted in greater usage of vancomycin, which may account for the rising incidence of vancomycin-resistant enterococci.