Changing epidemiology of bloodstream infection pathogens over time in adult non-specialty patients at an Australian tertiary hospital.

The epidemiology of bloodstream infections (BSI) has been changing over time in developed countries. However, overview reports of BSI trends are limited in Australia. This descriptive epidemiological study analysed general and age-group specific trends, and antimicrobial susceptibility patterns of blood culture isolates between 2001 and 2009 in non-specialty adult patients at an Australian tertiary referral centre. A total of 3,051 isolates from 2,172 patients (60% males) were analysed. Both community onset (1,790 isolates, 59%) and hospital onset (1,261 isolates, 41%) BSIs were included. The mean age of patients was 59 ± 20 years; 930 patients (43%) were 70 years of age or over. Overall, 1,493 (49%) gram positive bacteria, 1,389 (46%) gram negative bacteria and 169 (5.5%) fungi were isolated. The proportion of gram negative isolates increased over the 9 years, (44% to 53%, P = 0.006) whilst gram positives decreased (49% to 45%, P = 0.045). These trends were significant in community onset infections but not hospital onset infections, and also in adult patients aged 20 years to less than 70 years but not in the elderly (≥70 years). Gram negative pathogens were most prevalent amongst the elderly (53% in the ≥70 years age group, P<0.0001 vs. 41% in the ≥20 to <70 years age group), attributable to an age-dependent increase in Escherichia coli infections and a decrease in Staphylococcus aureus infections (P<0.0001 for both). Most gram negative isolates remained susceptible to commonly prescribed antibiotics. By contrast, methicillin-resistant S. aureus rates decreased from 54% in 2001 to 28% in 2009 (P=0.007). This study found that gram negative BSIs appeared to be re-emerging, particularly in community onset infections and also amongst the younger patients at the study institution. Such epidemiological trends have important implications for antimicrobial choices for the treatment of undifferentiated sepsis.