Studies reveal infectious disease inequality continues in NZ

Studies reveal infectious disease inequality continues in New Zealand
Invasive streptococcal infections also increasing in NZ

Embargo: 0:01H AEDT Thursday 27 March 2014

Thursday, 27 March (Adelaide): A study presented at this year’s Australasian Society for Infectious Diseases (ASID) meeting in Adelaide, Australia, shows that infectious disease inequality in New Zealand’s population is continuing, while rates of streptococcal and staphylococcal disease are well above the level seen in other developed countries.

Research by Dr Mark Hobbs (Auckland City Hospital and University of Auckland, NZ) and colleagues shows that, in a group of 6846 children born in 2009-2010 (the Growing Up in New Zealand study cohort), the risk of infectious disease hospitalisation was doubled for children of low birthweight compared with normal birthweight; increased by 34% for boys versus girls, increased by 2.5 times (or 150%) when born to a Pacific mother and by 1.5 times (or 56%) when born to a Maori mother compared with children born to mothers of New Zealand European ethnicity.

Children whose mothers smoked were 51% more likely to be hospitalised with an infectious disease. Those living in cities and urban areas were two thirds (66%) more likely to be hospitalised than those living rurally, and children placed in day care were 48% more likely to be hospitalised than children not placed in day care.

Dr Hobbs concludes: “Maori and Pacific children in NZ have a disproportionately high risk of admission with infection compared to New Zealand children of European ethnicity, consistent with that observed in Aboriginal children in Australia. The independence of the other risk factors identified indicates that interventions such as preventing low birthweight and smoke exposure are likely to benefit children irrespective of their ethnicity or household deprivation.”

He adds: “Regarding the increased risk in day care, young children in day care settings are exposed to a lot of bugs from the other children, and in some of these children this will lead to admission for chest infection or gastroenteritis or other problems depending on what they have caught.”

In other studies to be presented at the ASID meeting, Dr Deborah Williamson (Institute of Environmental Science and Research, Wellington and University of Auckland, NZ) and colleagues show that the incidence of invasive and non-invasive Staphylococcus aureus disease in New Zealand is among the highest reported in the developed world.

Using nationally collated hospital discharge data, Williamson and colleagues analysed the epidemiology of serious S. aureus infections in New Zealand between 2000 and 2011. The incidence of S. aureus skin and soft tissue infections (SSTI) increased significantly from 81 per 100,000 in 2000 to 140 per 100,000 in 2011, representing an increase of approximately 5% each year and 73% across the 11 years measured. Marked ethnic and sociodemographic inequality across all S. aureus infections was seen, with the incidence of all forms of S. aureus disease highest in Māori and Pacific Peoples (with rates of SSTIs three times higher in these populations than New Zealanders of European ethnicity) and in those patients residing in areas of high socioeconomic deprivation.

“This study is one of the few to assess trends in S. aureus disease across an entire nation,” says Dr Williamson. “The increase in S. aureus SSTIs, coupled with the observed demographic disparities, is of considerable concern. Future work should aim to reduce this disturbing national trend.”

A second study by Dr Williamson’s team showed that the incidence of invasive group A streptococcal infections (GAS) increased from 3.9 per 100,000 population in 2002 to 7.9 per 100,000 population in 2012. Alarmingly, this is well above the rate reported by other developed nations of between 2 and 4 per 100,000 population. Invasive group A streptococcus infections can cause conditions such as pneumonia, bacteraemia (which can lead to sepsis/septic shock), necrotising fasciitis (also known as flesh eating syndrome), and streptococcal toxic shock syndrome.

“The incidence was highest in the over 75-year age group, and in Pacific Peoples, with the incidence in Pacific Peoples almost seven times higher than in New Zealanders of European ethnicity,” says Dr Williamson.

She concludes: “The underlying reasons for the significant increase in invasive GAS infections in New Zealand are unclear, although possible contributory factors include increasing national rates of SSTIs or changes in the virulence of different types of circulating GAS strains.”

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