Infectious disease increases highlight inequality

An extensive analysis of New Zealand hospital records has found that admissions for serious infectious diseases increased 51 per cent in the last two decades.

The research, published in the leading international medical journal The Lancet and undertaken by Dr Michael Baker and his colleagues from the University of Otago, Wellington, also shows that Maori, Pacific Islanders and those in lower socioeconomic groups are disproportionately represented in hospital admissions for infectious diseases.

A full release from the University of Otago, with detailed findings from the study, can be found here.

The results are surprising given the international trend of infectious disease becoming less common in developed countries.

Key points from the research:

  • The researchers found that between 1989 and 2008 admissions for infectious diseases increased by 51.3%, while admissions for non infectious diseases increased by only 7.6% (age standardised rates).
  • The study is based on collated census data and an analysis of five million overnight hospital admissions for infectious and non-infectious diseases in NZ between 1989 and 2008.
  • Lower respiratory tract and skin infections were the most common reasons for admission due infectious disease.
  • Hospitalisations for serious infectious diseases are concentrated in two groups – under five years of age and the 70+ age group.
  • Rates of admission for infectious diseases in Pacific Islander and Maori populations are respectively 2.35 and 2.15 times higher than the for NZ Europeans and other ethnic groups.
  • Between 1989 and 2008, the rate of admission for infectious diseases increased by 72.1% for Pacific Islanders and 49.6% for Maori, with European New Zealanders and other ethnic groups increasing by 40.2%.

Commenting on the results Dr Baker said:

“What we expected to see was a steady decline in serious infectious diseases and a rise in admissions for chronic diseases, such as cancer and diabetes, which is the expected pattern for a developed country.”

The authors also note that in 2001 the Ministry of Health presented a strategic plan to reduce the incidence and burden of infectious disease. They state in their discussion “Our findings show a need to revisit these strategies” .

In an accompanying editorial in the Lancet Prof Stephen Lim and Prof Ali Mokdad, both from the University of Washington, Seattle, USA commented:

“These findings challenge the epidemiological transition theory, whereby development is accompanied by a shift of health burden towards chronic diseases, and have enormous implications for health and social policy in New Zealand.”

The Science Media Centre contacted experts in infectious diseases and epidemiology for comment. Feel free to use these quotes in your reporting. To speak to an expert, please contact the SMC (04 499 5476;

Dr Nikki Turner, Immunisation Advisory Centre Director and Senior Lecturer, General Practice & Primary Health Care at University of Auckland, comments:

“This is a really important study and it is a real credit to the authors and the quality of their work to get NZ data published in a rigorous highly esteemed international publication such as the Lancet.

“Overall the starkest message is that NZ has seen a consistent rise in the rates of infectious diseases from the early 1990s to recent times (data stops at 2008). This appears to be in contrast with other Western countries where absolute rates and the relative contribution on infectious diseases burden to hospitalization rates has been dropping i.e. generally as a country gets wealthier infectious diseases are better controlled and the disease burden shifts more to chronic conditions such as heart disease and cancers.

“What are the reasons for NZ being different?   It appears to be particularly linked to the rise in socioeconomic inequalities in our society. The burden of disease is falling disproportionately on some groups – in particular those from economically poorer environments and certain ethnic groups – with Maori and Pacific peoples carrying a heavy burden.  Furthermore the inequities over the past 20 years have grown so these groups are relatively getting even more sick than others.  There is something very wrong in NZ with such a stark and growing inequity burden.

“The factors involved will be multiple and be a mixture of the environment (housing conditions, heating, ), organism transmission (overcrowding, multiple infections making others more likely), host susceptibility ( issues that affect the immune response such as stress, poor nutrition) and possibly health seeking (ability to access to primary care, knowledge and health seeking).

“Overall those who are affected the most are young children, however interestingly the growth in rates and inequality has been lower in this age group than in others. We can speculate as to whether initiatives such as improving housing, better access to primary care, dropping household smoking rates  and improving rates of immunisation have contributed to this.  It is likely that the pneumococcal vaccination programme introduced in 2008 and the improving immunisation coverage rates and reducing inequalities with immunisation coverage will have continued to improve the situation for this group. Of note is that this data is only until 2008 however.

“I would advocate that despite some improvements this group [children] still carries the heaviest burden of infectious disease rates and ongoing inequities  and hence  NZ needs to focus further on preventive strategies  that include immunisations that other Western countries are now routinely delivering particularly varicella (chicken pox) vaccine to reduce skin infections, rotavirus v accine to reduce diarrhoeal diseases, meningococcal vaccine.  Other important preventive health strategies to continue to focus on are improving housing, heating, access to services and a stronger focus on family income  for the very low income families, all would be likely to have significant impact on our appalling rates of infectious disease.

“So in summary NZ has many people living in poverty and it makes our people sick, more so with Maori and Pacific communities.  There are economic, social and medical interventions that can and should be considered to address this problem and as a society we need to address this urgently. New Zealand’s historical approach to cherry pick a few solutions and not look at the overall dismal picture is not a sensible strategy.  We need strong leadership from the top and a national integrated approach to respond to the heath issues arising from significant social inequalities.”

Professor Cunningham, Director of Massey University’s Research Centre for Maori Health & Development, comments:

“Michael Baker’s important paper demonstrates the both the increasing incidence of infectious diseases and the increasing disparities between Maori/Pasifika and Pakeha New Zealanders over the two decades since 1989. This is the first ever report which has allowed a study of causal factors for infectious diseases at a country level over a long period of social, economic and health system change.

“The study identifies the ‘strong and independent effects’ of ethnicity and social deprivation resulting in a multiplicative effect on the risk of infection for Maori and Pasifika.  It shows that infectious diseases are becoming more important as a cause of hospitalisation.  Age – both the young and old – is also highly relevant.

“Exposures are a key mechanism with Maori households having more people and more children.  Chronic household overcrowding for Pasifika has also increased over the study period. The authors point out that the health transition theory – the transition in developed countries from infectious to non-infectious diseases – does not appear to hold with increasingly mixed and diverse patterns of diseases in evidence in NZ.

“The government’s recent focus on acute rheumatic fever in Maori children is to be applauded, albeit somewhat belatedly.  Yet further preventive health strategies for Maori and Pasifika are urgently needed if we are to reverse this disturbing trend in increasing disparities.”

Dr. Cameron Grant, Associate Professor at the University of Auckland and a paediatrician at Starship Children’s Hospital:

“This manuscript reports an important piece of work which describes at a national level the large and increasing burden that New Zealand experiences from communicable diseases, and in particular from the close contact infectious diseases that Michael Baker described more fully in his recent report.2

“My comments are mainly limited to children because that is where my expertise lies.

“Close contact infectious diseases are the respiratory, skin and enteric (faecal-oral) infections spread by person-to-person contact in the community for which humans are the only or the most important source.2  As this manuscript describes (Figure 2) they account for the bulk of the increase in serious infectious diseases.

“As this manuscript clearly shows the diseases that cause the 9 million or so deaths in children < 5 years old globally each year are the main causes of serious infectious disease in New Zealand. What factors are contributory? The same things that cause these diseases to remain the main causes of child death in the developing world. If we reduce the adverse effects of these factors we will decrease these diseases. The factors that need to be improved are:

  • Quality of indoor living environments and household crowding:  Houses in New Zealand are cold, damp and moudly.  The recent changes in cigarette smoking legislation that restrict the freedom of smoking in public places have had little impact upon secondary smoke exposure in children.  Most of their smoke exposure occurs in the household. We have recently shown that mould in the bedroom, smokers in the household and household crowding are factors that all increase the risk of young children being hospitalised with pneumonia in New Zealand.3
  • Nutrition during pregnancy and infancy:  Malnutrition (both maternal and infant) contributes to approximately half of the 9 million deaths that occur each year in the world for children less than 5 years old.45  Malnutrition is prevalent in New Zealand with the two predominant forms being energy excess and micronutrient deficiency.  Maternal and infant malnutrition are likely to be significant contributors to the excessive respiratory illness disease burden that affects New Zealand preschool aged children.6  Unlike other developed countries, for example the USA and the UK, New Zealand lacks nutritional policy which helps to secure a nutritious diet for women during pregnancy and for children during the critical first few years.7-10
  • Immunisation: Immunisation coverage in New Zealand has lagged behind many other countries for several decades.  There have been improvements in coverage in recent years with these improvements occurring since the introduction of national health targets and the identification of improved immunisation coverage as one of the first of these targets in 2007.1112
    Newer vaccines can prevent illnesses due to respiratory (conjugate pneumococcal vaccines) and gastrointestinal (rotavirus vaccine) infections.  New Zealand has had the conjugate pneumococcal vaccine on its schedule since 2008 but does not yet have the rotavirus vaccine on its schedule despite the WHO recommending in 2009 that this vaccine be used globally.

Varicella vaccine is another one that can help reduce serious disease in New Zealand.  Varicella (chickenpox) underlies many hospital admissions for serious skin and soft tissue infections every year.  New Zealand has a particular issue with skin infections.  Skin infection hospital admission rates in children doubled from 1990 to 200613. They are more than 3 time greater than rates in the USA14. The USA has had the varicella vaccine on its schedule since the 1990s. New Zealand still does not.


  • Case management:  Improved case management is a key area that has contributed to reductions in child deaths from serious infections in the developing world.15  New Zealand should improve the case management of children with infections.  For example, we recently showed that fewer than half of preschool aged children hospitalised with pneumonia have received antibiotics prior to hospital admission.  In many instances this is because of missed opportunities for appropriate antibiotic prescribing by health professionals in primary care.16

“Lastly and perhaps most importantly the population with the excessive rates of communicable diseases (those that are poor and or are of Maori or Pacific ethnicity) are also the population groups at greatest risk of subsequent non-communicable diseases.  One may lead to the other.17

“As the manuscript by Michael Baker and his team shows the serious infectious diseases are concentrated in the first few years of life.  To prevent these is going to require interventions that are effective during pregnancy and early infancy.  We need to focus our attention on these early years and take a life course approach to these issues.  By that I mean we need to understand what factors early in life, for example during pregnancy, lead to a children being hospitalised with a serious infection.  We must do this for the ethnic groups in New Zealand that have the greatest disease burden, namely Maori and Pacific children.  We must eliminate the current inequities in health that exist between indigenous and non-indigenous New Zealanders and in population subgroups such as Pacific children and children living in more deprived households.

“We are very fortunate to now have a new opportunity to do this.  This new opportunity is Growing Up in New Zealand, New Zealand’s new birth cohort study.  Growing Up in New Zealand is a longitudinal study that provides an up-to-date, population relevant picture of what it is like to be a child growing up in New Zealand in the 21st century. 6822 pregnant women and 4,404 of their partners were enrolled. Pregnant women were eligible if they lived in the Auckland, Counties-Manukau or Waikato District Health Boards and had an estimated delivery date between 25 April 2009 and 25 March 2010.  The Growing Up in New Zealand cohort consists of the 6846 newborns of these women.

“Growing Up in New Zealand is the first longitudinal study of its kind that has recruited and collected information from both mothers and their partners from before children are born.  It includes significant numbers of our M?ori, Pacific and Asian children as well as our European and other New Zealanders.18  Serious infections are one of the early points of focus of this project.”

Conflict of interest statement

Dr. Cameron Grant is an Associate Professor at the University of Auckland and a paediatrician at Starship Children’s Hospital.  He is the Associate Director of Growing Up in New Zealand.  He is a member of the New Zealand Ministry of Health Immunisation Technical Advisory Forum.


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2. Baker M, Telfar Barnard L, Zhang J, Verrall A, Howden-Chapman P. Close-contact infectious diseases in New Zealand: Trends and ethnic inequalities in hospitalisations, 1989 to 2008. . Wellington: : Housing and Health Research Programme, University of Otago., 2010.

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