The Communicable Disease Picture in New Zealand Today

• Introduction
• Communicable Disease in New Zealand - Overview of the Impact on Our Society
• The Communicable Disease Picture in New Zealand Today
  • Focus on Vaccine Preventable Diseases
    • Measles
    • Pertussis (Whooping Cough)
  • Focus on Non-Vaccine Preventable Diseases
    • Enteric Disease
    • Meningococcal Disease
    • Rheumatic Fever
  • Focus on Emerging Diseases
  • Focus on Sexually Transmitted Diseases
• Enhancing Communicable Disease Prevention
• International Strategies to Prevent Communicable Diseases
• Future Challenges - Research and Policy
• References

Introduction

As the new millennium begins, and we celebrate the accomplishments of the last century, it is both timely and sobering to review New Zealand’s performance in disease prevention and health promotion. This paper focusses particularly on communicable disease, because all communicable diseases are preventable in some way. Nonetheless New Zealand has relatively high rates of such diseases compared with other developed countries, and rates have failed to decline at the pace that might have been expected. Increasingly, new diseases are emerging and ’old diseases’ are re-emerging here. New Zealand has good surveillance systems so disease trends and the effectiveness of prevention programmes are easily monitored. Surveillance gives early warning of emerging communicable disease issues that require an active response.

As well as collecting public health surveillance information, scientists are increasingly able to interpret these data, learning to understand the complex interactions between the human host, pathogenic organisms and the environment that lead to disease. This puts science in a better position to inform policy- and decision-making by predicting events and identifying intervention options. The country as a whole, and particularly vulnerable sectors within the community, stand to benefit greatly from properly designed disease prevention and health promotion programmes. Lack of resources for disease surveillance, prevention and control is partly responsible for New Zealand’s high rates of communicable disease. Another factor is community perceptions of prevention programmes, like vaccination, that can be barriers to uptake. Public antagonism toward irradiation, as a microbiological food safety tool, is another example. It is a big challenge to better understand these attitudes and deal with them appropriately.

Communicable Disease in New Zealand - Overview of the Impact on Our Society

Between 1989 and 1993, 6.9% of deaths were caused by communicable disease, the fourth major cause of death in New Zealand behind cardiovascular disease, cancer and death from injury. Indeed this figure may represent an underestimate because of data coding limitations.  ¹   This burden of illness and death impacts enormously on both individuals and the community as a whole.

Approximately 63,000 New Zealanders were admitted to public hospitals with communicable diseases in 1996-97, around 10% of admissions. Acute respiratory and gastrointestinal infections were the predominant causes of admissions for communicable diseases.  ²   As a consequence, loss of productivity and the personal and social costs of ensuing chronic disease in survivors, often requiring ongoing access to health resources, are high. This burden of illness is not distributed evenly throughout the community. Maori, Pacific Islands people, the very young and the elderly are disproportionately represented.  ³  

The Communicable Disease Picture in New Zealand Today

Focus on Vaccine Preventable Diseases
New Zealand has higher rates of some vaccine preventable diseases than comparable developed countries as shown in Table 1. In particular, New Zealand continues to experience periodic measles and pertussis epidemics. These epidemics are directly attributable to New Zealand’s low rates of vaccination. New Zealand was well behind its 1997 coverage target of 85%, with only 63.1% of children fully immunised by the age of two years in the Northern region in a 1996 survey.  ⁴   We are unlikely to come close to the year 2000 target of 95% vaccination coverage.

Measles
When, as a result of low vaccination rates, there are sufficient numbers of vulnerable children in the community, epidemics of measles will occur  ¹⁰   (Figure 1). Measles vaccination coverage is poor and, predictably, such epidemics continue to happen in New Zealand every three to five years.

Figure 1: Measles Epidemics - Laboratory Confirmed and Notified Cases by Year, 1980-1998. Source: ESR surveillance centre.

Most cases of measles occur in autumn and winter. In the 1997 epidemic, by far the majority of cases occurred in the North Health Region, with Pacific Islands children from 0-1 year old the most susceptible.  ¹¹   Such clear cut health disparities indicate that prevention and control strategies are not sufficiently well targeted at, or taken up by, the most vulnerable groups. It is a matter of urgency to design and deliver appropriate preventive childhood vaccination programmes. To succeed in this, it is necessary to know as much about the determinants of social behaviour as we do about the science of immunology that underpins vaccination.

Pertussis (Whooping Cough)
New Zealand is also experiencing periodic pertussis epidemics  ¹²   (Figure 2). Like measles, pertussis was made a notifiable disease in 1996 so knowledge about the incidence of disease before then is much less complete than it is today. The effect of pertussis infection can be devastating, particularly in children under 6 months of age where it carries a case-fatality rate of 0.5% as well as causing long term neurological complications among some of the survivors.  ¹³   But vaccination is not without risk either, with many children experiencing minor adverse events such as fever and redness, swelling and pain at the injection site. Rarely, children may have more serious reactions such as collapse and convulsions. When there is a perceived low risk of infection, caregivers may not wish to risk vaccinating their children, resulting in a larger pool of unvaccinated children and more frequent epidemics. It is important to educate caregivers so they can make informed choices about vaccinating their children.

Figure 2: Pertussis Epidemics - Laboratory Confirmed and Notified Cases by Year, 1980-1998. Source: ESR surveillance centre.

Focus on Non-Vaccine Preventable Diseases

Enteric Disease
The incidence of enteric disease is also high in New Zealand compared to countries of a similar type (Table 2).

Table 2: Enteric Diseases, 1997 [Rates expressed as cases per 100,000 population]

Sources: New Zealand   ⁵  , Australia   ⁶  , USA   ⁷  , Canada   ⁸  , UK   ⁹  

In particular, New Zealand has the highest reported rates of campylobacteriosis in the developed world, with this rate reaching as high as 320 per 100,000 population in 1998 (Figure 3). Campylobacteriosis is estimated to cost New Zealand over $40 million per year through lost productivity and other costs.  ¹⁴   At least some of this burden of disease should be preventable with improved food safety programmes.

Figure 3: Campylobacteriosis Cases by Year, 1980-1998. Source: ESR surveillance centre.

The incidence of cryptosporidiosis and giardiasis is also high with cryptosporidiosis cases having increased to 23.9 per 100,000 in 1998 thanks to swimming pool related outbreaks in the Wellington region  ¹⁵   and high rates in some of New Zealand’s more rural health districts such as Waikato, Hawkes Bay, Manawatu and Canterbury (Figure 4)

Figure 4: Cryptosporidiosis Cases by Month, 1996-1999. Source: ESR surveillance centre.

Cryptosporidiosis rates are also linked to the quality of the drinking water supply. The lowest rates occur in areas with completely satisfactory public health grading for the water source, treatment and distribution. The highest rates of disease occur in areas where water is ungraded or where grading is unsatisfactory.  ¹⁶   Disease prevention can be achieved by upgrading water supplies in areas where the grading and compliance with standards are poor.

Prevention and control of gastrointestinal disease requires a more integrated approach to food safety than the sector-based approaches taken at present in New Zealand. An understanding of the ecology of pathogens is essential to reversing New Zealand’s poor record with regard to preventing enteric disease, which imposes both a huge economic burden on the country as well as discomfort for those infected. Enteric disease can be fatal for vulnerable members of the population. Shortcomings in food safety practices are a significant threat to New Zealand’s trade as an exporter of primary produce and as a ’clean green and blue’ tourist destination.

Probably the most important emerging enteric disease in the developed world is verotoxigenic E. coli (VTEC), the best known form of the organism being E. coli 0157. This disease may cause haemolytic uraemic syndrome (HUS) which has a case fatality rate of 3-5% and results in serious long term effects in 12-30% of survivors.  ¹⁷   The incident of VTEC infection in New Zealand has risen markedly since 1997 (Figure 5). There have been serious outbreaks elsewhere  ¹⁸   and it is probably only a matter of time before there is a large outbreak in New Zealand. The sources and modes of transmission are not known in New Zealand and require further research before prevention and control strategies can be implemented.

Figure 5: Verotoxigenic E. coli Cases by Year, 1980-1998   ¹⁷  

Scientific advances in microbiology at the molecular level are also allowing us to recognise viral enteric disease more easily than in the past. Experts now believe that there has been significant under-reporting of viruses causing enteric disease.  ¹⁹  

Rates of occupational zoonotic diseases like leptospirosis, that largely affect farm workers and those in the meat industry, are also higher in New Zealand than in Australia, Canada, the US, England, Wales and Scotland even though the New Zealand rates have been steadily declining since 1980. Evidence also shows significant under-reporting of this disease.  ²⁰  

Meningococcal Disease
New Zealand is in its tenth year of a meningococcal serogroup B epidemic which has seen 3,066 cases from 1991 to 1999 inclusive; 142 of these cases have been fatal.  ^{21  ,   22}  Prior to 1991 there were usually around 50 cases per year mostly involving serogroups B and C meningococci.  ²³  The highest rates of the disease are found among Maori and Pacific Island populations living in the Northern region of New Zealand (Figure 6).

Figure 6: Meningococcal Disease - Northern Region of New Zealand, by Ethnicity, 1991-1998   ²¹  

Currently there is no serogroup B vaccine appropriate for New Zealand’s epidemic. Therefore, the best means of prevention and control is an understanding of the disease’s risk factors. A research project to identify these risk factors is nearly completed and the findings will be available during 2000.

Rheumatic Fever
Rheumatic fever is another disease where New Zealand has unenviable third world statistics. In 1997 the rate was 2.6 cases per 100,000 compared to less than 0.1 cases per 100,000 in Australia  ⁶  , United States  ⁷  , Canada  ⁸  , England, Wales and Scotland.  ⁹   Acute rheumatic fever is a serious but preventable disease. There is an average of 145 new admissions to hospital each year in New Zealand. Most of these (84%) are Maori and Pacific Islands people.  ²⁴  Chronic rheumatic heart disease is a serious sequela to the acute disease and is responsible for around 915 hospital admissions each year and 124 deaths.  ²⁴   There has been a disturbing increase in chronic rheumatic heart disease hospitalisations in recent years (Figure 7). This large burden of disease has prompted a randomised controlled-trial to determine if a school-based programme of sore throat intervention will significantly decrease the rate of rheumatic fever in South Auckland school children.

Figure 7: Chronic Rheumatic Heart Disease Hospitalisations, 1970-1997   ²⁴  

Focus on Emerging Diseases
’Emerging’ communicable diseases are ’infections that have newly appeared in a population or have existed but are rapidly increasing in incidence or geographic range’.  ²⁵   This process is aided and abetted by a range of factors including a more mobile global population, climate change, and sometimes new technologies. The spread of Creutzfield-Jacob disease, for example, was facilitated by changes in the food processing sector. ’Old enemies’, like pneumococci, are re-emerging because of new-found antibiotic resistance. Others, such as diphtheria in the former Soviet Union, re-emerged following the breakdown of co-ordinated public health measures. Improved laboratory methods have allowed evolving epidemics to be recognised, particularly those caused by viruses such as HIV and hepatitis C.

There are several exotic diseases notified in New Zealand that are associated primarily with migration and travel. All cases of malaria (73), dengue fever (26) and leprosy (2) reported in 1998 were acquired overseas.  ⁵   Malaria and dengue fever notifications have increased in the 1990s suggesting that more effort should go into ensuring travellers take precautions to prevent insect bites and use antimalarial medication. Mosquitoes with the ability to transmit Ross River virus have been recently introduced to New Zealand and an eradication programme is in progress.  ²⁶   We are also seeing an increase in the incidence of tuberculosis with more cases occurring within the New Zealand-born population than in the past.  ²⁷  

Focus on Sexually Transmitted Diseases

The high incidence of sexually transmitted diseases, especially chlamydia and gonorrhoea is of real concern. A recent study in the Waikato and the Bay of Plenty estimated the incidence of STDs in the population for the region. The incidence of chlamydia infection was greater than for Canadian  ²⁸   and US women.  ²⁹   The incidence of gonorrhoea infection here is greater than in Canada but below that in the US.  ³⁰   These diseases are preventable but prevention is dependent on education and an efficient and well-resourced community-based health service infrastructure.

Enhancing Communicable Disease Prevention

Strategies for communicable disease prevention include:

• reducing or eliminating the source of the pathogenic organism
• modifying environmental factors
• modifying social behaviour
• modifying diet or poor hygiene
• providing accessible health care
• providing vaccination
• using antibiotics wisely.

In general, prevention strategies achieve more than control strategies. For example, progress is being made towards preventing complications from influenza infection by vaccinating vulnerable population groups against the prevalent virus strains, ascertained through surveillance activities.

A strong argument for communicable disease prevention is the cost, in social and economic terms, of not preventing these diseases. Research provides both the knowledge and the tools to enable prevention. Priority areas are those where there will be maximum health gain. The meningococcal epidemic is already estimated to have cost New Zealand tens of millions since 1991. In 1991, the hospital-associated costs of rheumatic fever and rheumatic heart disease in Auckland alone are estimated to have been $3.6 million.  ³¹   There are wide benefits from research: government health authorities use research information to support policy decisions, to justify legislation and to prioritise resources; clinicians apply new knowledge to their decisions and treatment; and the medical industry develops innovative new products where there is a market.

International Strategies to Prevent Communicable Diseases

National and international responses are needed to address communicable diseases. For example, the US Institute of Medicine Report Emerging Infections - Microbial Threats to Health in the United States   ³²   recommended strategies for the US to detect and control these threats. The strategies include according high priority to emerging communicable diseases, having a co-ordinated and ecological focus, having high quality specialist laboratory services, surveillance and communication networks and an effective public health infrastructure with rapid response mechanisms and epidemic preparedness.

International strategies are needed to combat antimicrobial resistant organisms. Such organisms’ increasing resistance to antibiotics is rendering current therapies ineffective. Methicillin-resistant Staphylococcus aureus (MRSA) is almost endemic in New Zealand hospitals and vancomycin-resistant enterococci and multi-resistant pneumococci mean that new antimicrobials are needed along with effective protocols for their use.  ^{33  ,   34}  

Antiviral agents are also needed. There is much internationally-based research in this area and it is important to manage the emergence of resistance to antiviral agents.  ³⁵  

Today’s society has learned a lot from past successes. Smallpox has been eradicated and polio is near eradication globally. In New Zealand we have had successful brucellosis eradication  ³⁶   and hydatids control. We have eliminated cases of and deaths from diphtheria and have recently seen marked declines in Hib (Haemophilus influenza type b)  ³⁷   and hepatitis B   ³⁸   as a result of vaccination. But there is no room for complacency since New Zealand’s first case of diphtheria since 1980 has been seen recently.  ³⁹  While it is possible and sensible to ’import’ research findings from overseas, it cannot be assumed that findings from other countries will apply here. New Zealand has a unique ethnic mix, a different physical environment to many other regions and its own social issues.

Future Challenges - Research and Policy

New Zealand research needs to be issue-focussed and multifaceted and involve discipline-based scientists, clinicians, public health workers, social scientists and environmental scientists. Clearly, the priorities must be to investigate new and re-emerging infectious agents, antimicrobial resistance and communicable diseases associated with disparities and with social and economic importance. Research must investigate disease risk factors, dietary issues predisposing to infection, genetic pre-disposition to disease, organism-host interactions and immunisation issues. There are real opportunities to provide knowledge of global importance by conducting clinical trials of new treatment strategies and studying the effectiveness of community intervention trials in New Zealand. It is important to retain our world-class research scientists and encourage the development of human capital in environmental health.

But research alone will not improve New Zealand’s communicable disease statistics. Science must inform policy. Scientists and policy makers, often from across government agencies, need to develop partnerships for problem-solving and decision-making. There is still plenty of scope to ’work smarter’ on disease prevention - and to benefit our society as a whole - a real challenge for the new millennium.

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