The Lancet  
Mar 24, 2012  Volume 379  Number 9821  p1075 – 1170
http://www.thelancet.com/journals/lancet/issue/current

Editorial
Social determinants of health and outcomes in New Zealand
The Lancet
Preview
In this issue of The Lancet, Michael Baker and colleagues analyse more than 5 million hospital admissions in New Zealand for infectious diseases. Two messages stand out. First, hospitalisations ascribed to infection have risen in both absolute terms (by more than 25 000 per year) and as a proportion of overall acute admissions (from 20·5% in 1989–93 to 26·6% in 2004–08). Second, the risk of hospitalisation for serious infectious diseases in New Zealand is borne disproportionately by Māori and Pacific peoples and by those who are socioeconomically disadvantaged.

Comment
Socioeconomic inequalities and infectious disease burden
Stephen S Lim, Ali H Mokdad
Preview
Valid, reliable, comparable, and timely statistics for levels, trends, and inequalities in morbidity and mortality by cause are essential to monitor progress towards improvements in population health, and to plan the delivery of health services. In The Lancet, Michael Baker and colleagues1 describe trends and inequalities in hospital admissions for infectious and non-infectious diseases by cause between 1989 and 2008. With use of a national hospital database in New Zealand, the investigators noted a relative increase of 51.3% in the age-standardised rate of hospital admissions for infectious diseases from 1989–93 to 2004–08, with the greatest increase noted in the indigenous Māori (age-standardised rate ratio 2·15, 95% CI 2·14–2·16) and Pacific peoples (2·35, 2·34–2·37) compared with those of European or other ethnic grouping; and in the most socioeconomically deprived quintile (2·81, 2·80–2·83) compared with the least deprived quintile.

Articles
Increasing incidence of serious infectious diseases and inequalities in New Zealand: a national epidemiological study
Michael G Baker, Lucy Telfar Barnard, Amanda Kvalsvig, Ayesha Verrall, Jane Zhang, Michael Keall, Nick Wilson, Teresa Wall, Philippa Howden-Chapman
Summary
Background
Although the burden of infectious diseases seems to be decreasing in developed countries, few national studies have measured the total incidence of these diseases. We aimed to develop and apply a robust systematic method for monitoring the epidemiology of serious infectious diseases.

Methods
We did a national epidemiological study with all hospital admissions for infectious and non-infectious diseases in New Zealand from 1989 to 2008, to investigate trends in incidence and distribution by ethnic group and socioeconomic status. We extended a recoding system based on the ninth revision of international classification of diseases (ICD-9) to the tenth revision (ICD-10), and applied this to data for hospital admissions from the New Zealand Ministry of Health, National Minimum Dataset. We filtered results to account for changes in health-care practices over time. Acute overnight admissions were the events of interest.

Findings
Infectious diseases made the largest contribution to hospital admissions of any cause. Their contribution increased from 20·5% of acute admissions in 1989—93, to 26·6% in 2004—08. We noted clear ethnic and social inequalities in infectious disease risk. In 2004—08, the age-standardised rate ratio was 2·15 (95% CI 2·14—2·16) for Māori (indigenous New Zealanders) and 2·35 (2·34—2·37) for Pacific peoples compared with the European and other group. The ratio was 2·81 (2·80—2·83) for the most socioeconomically deprived quintile compared with the least deprived quintile. These inequalities have increased substantially in the past 20 years, particularly for Māori and Pacific peoples in the most deprived quintile.

Interpretation
These findings support the need for stronger prevention efforts for infectious diseases, and reinforce the need to reduce ethnic and social inequalities and to address disparities in broad social determinants such as income levels, housing conditions, and access to health services. Our method could be adapted for infectious disease surveillance in other countries.

Funding
New Zealand Ministry of Health, New Zealand Health Research Council.