Trends in Bacteremia Over 2 Decades in the Top End of the Northern Territory of Australia

Abstract

Background: Information on the local distribution of bloodstream pathogens helps to guide empiric antibiotic selection and can generate hypotheses regarding the effectiveness of infection prevention practices. We assessed trends in bacterial blood culture isolates at Royal Darwin Hospital (RDH) in the Northern Territory of Australia between 1999 and 2019.

Methods: Species identification was extracted for all blood cultures first registered at RDH. Thirteen organisms were selected for focused analysis. Trends were examined graphically and using univariable linear regression.

Results: Between 1999 and 2019, 189 577 blood cultures from 65 276 patients were processed at RDH. Overall, 6.72% (12 747/189 577) of blood cultures contained a bacterial pathogen. Staphylococcus aureus was the most common cause of bacteremia during the first decade, with an estimated incidence of 96.6 episodes per 100 000 person-years (py; 95% CI, 72.2-121/100 000 py) in 1999. Since 2009, S. aureus bacteremia has declined markedly, whereas there has been an inexorable rise in Escherichia coli bacteremia (30.1 to 74.7/100 000 py between 1999 and 2019; P < .001), particularly in older adults. Since 2017, E. coli has been more common than S. aureus. Rates of Streptococcus pneumoniae bacteremia have reduced dramatically in children, while Burkholderia pseudomallei remained the fourth most common bloodstream isolate overall.

Conclusions: The incidence of S. aureus bacteremia, though high by international standards, is declining at RDH, possibly in part due to a sustained focus on both community and hospital infection prevention practices. Gram-negative bacteremia, particularly due to E. coli, is becoming more common, and the trend will likely continue given our aging population.

Keywords: Australia; Escherichia coli; Northern Territory; Staphylococcus aureus; bacteremia.

Figure 1.

Study profile.

Figure 2.

Trends in numbers and positivity of blood cultures received at Royal Darwin Hospital Laboratory between 1999 and 2019. A, Numbers are broken down by positivity. B, Percentage of all blood cultures containing a bacterial pathogen or a low-pathogenicity organism. C, Total blood cultures received by age group. D, Percentage of blood cultures containing a pathogen by age group.

Figure 3.

Number of episodes of bacteremia per 100 blood cultures received (A and C) and incidence of bacteremia per 100 000 person-years (B and D) for individual bacterial organisms or groups of organisms. Abbreviations: A, Acinetobacter species; BP, Burkholderia pseudomallei; E, Enterococcus species; EC, Escherichia coli; ES, other ESCAPPM organisms; GAS, Group A Streptococcus; HS, other hemolytic streptococcal species; K, Klebsiella species; PR, Pseudomonas aeruginosa; PS, Proteus species; py, person-years; S, nontyphoidal Salmonella species; SA, Staphylococcus aureus; SP, Streptococcus pneumoniae.

Figure 4.

Number of episodes of bacteremia per 100 blood cultures received (A, C, and E) and incidence of bacteremia per 100 000 person-years (B, D, and F). A and B, Patients of all ages. C, D, E, and F, broken down by age group. Abbreviation: py, person-years.