Incidence, trends and demographics of Staphylococcus aureus infections in Auckland, New Zealand, 2001-2011

Abstract

Background: New Zealand has a higher incidence of Staphylococcus aureus disease than other developed countries, with significant sociodemographic variation in incidence rates. In contrast to North America, the majority of disease is due to methicillin-susceptible S. aureus (MSSA), although relatively little is known about the comparative demographics of MSSA and methicillin-resistant S. aureus (MRSA) infections in New Zealand.

Methods: Our objectives were to describe the trends, incidence and patient demographics of all S. aureus infections in patients presenting to our institution between 2001 and 2011, and compare the epidemiology of MSSA and MRSA infections. We identified all patients with S. aureus infections over the study period. A unique S. aureus infection was defined as the first positive S. aureus culture taken from the same patient within a thirty-day period. Standard definitions were used to classify episodes into community- or healthcare-associated S. aureus infection.

Results: There were 16,249 S. aureus infections over the study period. The incidence increased significantly over the study period from 360 to 412 per 100,000 population (P < 0.001), largely driven by an increase in community-associated non-invasive MSSA infections. When compared with MSSA infections, patients with non-multiresistant MRSA infections were more likely to be older, have hospital-onset infections and be Māori or Pacific Peoples.

Conclusions: Our work provides valuable baseline data on the epidemiology and trends of S. aureus infections in New Zealand. The significant increase in community-associated S. aureus infections is of public health importance. Future studies should investigate the reasons underlying this concerning trend.

Figure 1

Incidence of Staphylococcus aureus infections per 100,000 population per year in patients hospitalized at Auckland District Health Board, New Zealand, 2001–2011, stratified by (A) place of acquisition; (B) invasive vs. non-invasive infection and (C) MSSA vs. MRSA. Abbreviations: CA, community-associated; HCA-CO, healthcare-associated, community-onset; HCA-HO, healthcare-associated, hospital-onset; MSSA, methicillin-susceptible Staphylococcus aureus; MRSA, methicillin-resistant Staphylococcus aureus; NS, not significant.

Figure 2

Incidence of Staphylococcus aureus infections per 100,000 population per year in patients hospitalized at Auckland District Health Board, New Zealand, 2001–2011, stratified by (A) age; (B) ethnicity; and (C) NZDep score according to (i) place of acquisition and (ii) MSSA, nmMRSA and mMRSA. Abbreviations: CA, community-associated; HCA-CO, healthcare-associated, community-onset; HCA-HO, healthcare-associated, hospital-onset; MSSA, methicillin-susceptible Staphylococcus aureus; MRSA, methicillin-resistant Staphylococcus aureus; NZDep, New Zealand Deprivation Index (1 = least deprived, 10 = most deprived).