4102.0 - Australian Social Trends, 1997
ARCHIVED ISSUE Released at 11:30 AM (CANBERRA TIME) 19/06/1997
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Mortality & Morbidity: Infectious diseases
Mortality since 1921 In Australia, the general pattern of mortality decline over this century has been the declining significance of infectious diseases and the increasing significance of chronic diseases such as cancer and diseases of the circulatory system, and deaths due to motor vehicle and other accidents. Between 1921 and 1995, death rates from infectious diseases declined faster than deaths from all causes. Age-standardised death rates from infectious diseases fell from 185 per 100,000 population in 1921 to six in 1995. Over the same period, standardised death rates from all causes fell from 1,567 per 100,000 to 645. As a proportion of all deaths, infectious diseases declined from 19% in 1921 to 1% in 1995. One of the most dramatic declines in death rates has been for tuberculosis. Age-standardised death rates from tuberculosis fell from 75 per 100,000 in 1921 to 0.4 in 1995. The decline in deaths from infectious diseases has been attributed to a range of social and demographic changes, public health measures and medical advances. AGE-STANDARDISED(a) DEATH RATES
Source: Australian Institute of Health and Welfare (unpublished data); Estimated Resident Population by Sex and Age: States and Territories of Australia (cat. no. 3201.0). Current mortality, 1991-95 Of all deaths in the period 1991-95, 1% were due to infectious diseases. As with deaths from all causes, the risk of dying from infectious diseases was higher among infants in the first year of life (7 deaths per 100,000 infants) than for older children and adults aged up to their mid fifties, but increased rapidly among the elderly population. Death rates from infectious diseases were highest for septicaemia (2.6 per 100,000), viral hepatitis (0.6), and intestinal infections (0.4). However the risk of death from different types of infectious disease varied by age. Infants under one year who died from an infectious disease during the period 1991-95 were most likely to die from Meningococcal Infection (2.4 per 100,000 population), Intestinal Infection (1.4) or Septicaemia (0.9). The risk of dying from an infectious disease generally increased with age. Meningococcal infection was one exception to this pattern, with rates generally decreasing with age. The increase in risk with age was most evident for septicaemia. During the period 1991-95, the risk of a person aged 75 and over dying from septicaemia was 44 times higher than for infants in the first year of life, and 12 times higher than for adults aged 55-74. In contrast, the risk of people aged 75 and over dying from viral hepatitis was 12 times higher than an infant dying of this disease, and much the same as for people aged 55-74. Some population groups experience deaths at rates much higher than the national average. In 1995, age-standardised death rates from infectious diseases were four times higher for Indigenous people than for the total population3. AGE-STANDARDISED DEATH RATES(a) FROM INFECTIOUS DISEASES (a) Standardised death rate per 100 000 of the 1991 population (see p. 42 for explanation of age standardisation). Source: Australian Institute of Health and Welfare (unpublished data); Estimated Resident Population by Sex and Age: States and Territories of Australia (cat. no. 3201.0). Notifiable diseases Notification of many infectious diseases to State and Territory health authorities is required to identify, prevent and control outbreaks4. The Communicable Diseases Network - Australia New Zealand, collates national data on notifications of infectious diseases. Notifications data need to be interpreted with caution, because not all diseases are notifiable in each State and Territory. Furthermore, owing to under-reporting, notifications are likely to underestimate the actual incidence (that is, the number of new cases each year) of disease. Despite these limitations, notifications data are the best available estimates of the incidence of various infectious diseases. AGE-SPECIFIC DEATH RATES(a) FROM INFECTIOUS DISEASES, 1991-95 (a) Rate per 100,000 population aged 0-75. Source: Causes of Death, Australia (cat. no. 3303.0 and unpublished data); Estimated Resident Population by Sex and Age: States and Territories of Australia (cat. no. 3201.0). Intestinal infections Diarrhoea is the most common symptom of intestinal tract infections and is caused by a range of different organisms. However, because it is usually in a mild form, people do not always seek medical attention, and it is often unreported. Worldwide, diarrhoea remains one of the most important causes of ill-health and death among infants and children. In developed countries the incidence is much lower, but still significant. Better hygiene and clean water, as well as increased rates of breastfeeding have all contributed to the decline in the incidence of diarrhoeal disease among infants in Australia. Because many intestinal infections are transmitted through food, the quality of food production and distribution is an important aspect of prevention. AGE-SPECIFIC DEATH RATES(a), 1991-95
Source: Causes of Death, Australia (cat. no. 3303.0 and unpublished data); Estimated Resident Population by Sex and Age: States and Territories of Australia (cat. no. 3201.0). Vaccine-preventable disease The incidence of vaccine-preventable diseases has fallen markedly over the century. Notification rates for diphtheria, measles, mumps, whooping cough, polio, rubella, tetanus and tuberculosis have all declined since the early part of this century. One of the most dramatic declines has been for tuberculosis, falling from a peak of 90 cases per 100,000 population in 1918 to 6 in 1995. The decline in the incidence of polio has been another success of immunisation. Rates fell from a peak of 39 per 100,000 in 1938, to the last notification in 1986 (one notification only). Global eradication of smallpox was declared by the World Health Organisation in 1980, and the last known natural case (that is, not contracted from laboratory work) of smallpox was in Somalia in 19775. The last notification of smallpox in Australia was in 1921, and of bubonic plague in 1922. While the incidence of vaccine-preventable diseases has fallen, cases still occur, highlighting the importance of maintaining vaccination programs. In 1995 over 4,000 cases of whooping cough were notified (a rate of 24 per 100,000) (see Australian Social Trends 1997, Protecting the health of our children). NOTIFICATION RATES OF SELECTED(a) INFECTIOUS DISEASES, 1995
(b) Rate per 100,000 population. When a disease is not notifiable in all States and Territories, the population of only those States and Territories in which the disease is notifiable, was used in calculating rates. Source: Department of Health and Family Services Communicable Diseases Intelligence, Vol. 20 No. 21, October 1996. Mosquito-borne infections Malaria was endemic in northern Australia early this century. The last epidemic was in the Northern Territory in 1962, and Australia was declared malaria free by the World Health Organisation in 1981. However, the number of imported cases has risen steadily since then. In 1995, the notification rate for malaria was 3.5 per 100,000. It is possible that malaria may in the future become re-established in the north of Australia, because mosquitoes capable of transmitting the virus to humans are present there. Other mosquito-borne infections of public health significance in Australia include the arbovirus infections; Dengue, Ross River and Barmah Forest Viruses. Notification rates for these infections in 1995 were 0.2, 14, and 5 per 100,000 respectively. Sexually transmitted diseases (STDs) The incidence of gonococcal infection (which includes gonorrhoea) and syphilis has fallen since the early part of this century. Furthermore, developments in treatment have led to vastly improved outcomes for people infected with STDs. The peak notification rate of gonococcal infection occurred in 1917 with 315 notifications per 100,000, falling to 183 in 1928. 18 cases of gonococcal infection per 100,000 population were notified in 1995. Syphilis notification rates are available for the periods between 1917 and 1929, and 1968-69 to 1995. The peak notification rate was in 1920 at 173 notifications per 100,000. Ten cases per 100,000 were notified in 1995. Rates of both gonococcal infection and syphilis increased in the 1970s and declined in the late 1980s. Some of this decline may be due to changes in sexual behaviour associated with the public health education campaign against HIV/AIDs infection. However, notification rates for some other STDs including HIV/AIDS and chlamydia have increased over recent years, although the incidence of HIV infection now appears to have peaked (see Australian Social Trends 1997, Acquired immunodeficiency syndrome). Hepatitis Hepatitis means inflammation of the liver and results from a range of causes, including viruses, bacteria and protozoa, as well as drugs and toxins. Hepatitis A, B and C are the most common forms of viral hepatitis in Australia. Hepatitis A is the most common, and generally least serious, form of viral hepatitis. It is usually transmitted through infected food or water. Notification rates fell from a peak of 123 per 100,000 in 1961 to 9 in 1995. Hepatitis B is generally transmitted by blood transfusion, sharing of needles, intimate personal contact (especially sexual), or from mother to baby. Hepatitis B is usually more serious than hepatitis A, and some people become chronic carriers after recovery. Hepatitis B notifications increased from 0.7 per 100,000 in 1971 to 1.8 in 1995. Some of this increase may be due to improved diagnosis. Hepatitis C was first identified in 1990. It is the most common form of hepatitis transmitted by blood transfusion, but can also be transmitted by sharing needles. People infected with this virus do not always have symptoms. However about 50% of people with acute hepatitis C develop chronic hepatitis. Notifications data for hepatitis C are not considered to be a reliable guide to incidence (that is, the number of new cases in a year). The incidence of hepatitis C was estimated at 8 cases per 100,000 in 1995. Serious long-term complications such as cirrhosis and liver cancer can develop from infection by hepatitis virus, particularly from types B and C. Zoonoses Notifications of cases of the following zoonotic diseases (that is, diseases which can be transmitted from animals to humans) were received in 1995: Brucellosis (0.2 cases per 100,000), Hydatid Infection (0.3), Leptospirosis (0.8), Ornithosis (1.5), and Q Fever (2.6). A recent case of a zoonotic infection by a previously unknown agent was transmission o f Equine Morbillivirus from horses to humans in Queensland, resulting in two human deaths6. Another newly identified virus (lyssavirus) has since been found in fruit bats in Queensland, and one human death has resulted from infection by this virus7. Notification rates of other zoonotic diseases including Leptospirosis, Q Fever and Brucellosis have all declined in recent decades. Other infectious diseases Other infectious diseases with notification rates of at least 0.5 per 100,000 in 1995 include legionellosis (0.9 per 100,000) and meningococcal infection (2.1). Legionnellosis was first notifiable in 1979. Notification rates for this infection, generally transmitted by airconditioning systems and spas, have been fairly steady between 1991 and 1995. Notifications of meningococcal infection are available from 1949 to 1967-68, and from 1979 to 1995. Notification rates peaked at 6 cases per 100,000 in 1952, and declined to 0.3 in 1982. Rates have increased since then, and were 2.1 per 100,000 in 1995.
Endnotes 1 Nutbeam, D. 1993, Goals and Targets for Australia's Health in the Year 2000 and Beyond, University of Sydney, Sydney. 2 Australian Bureau of Statistics 1995, Children's Immunisation Australia, cat. no. 4352.0, ABS, Canberra. 3 Australian Bureau of Statistics, Causes of Death (unpublished data); Estimated Resident Population (unpublished data); Experimental Projections of the Aboriginal and Torres Strait Islander Population (unpublished data). This figure is based on data from South Australia, Western Australia and the Northern Territory only, and is standardised to the total 1995 population. 4 Department of Health and Family Services Communicable Diseases Intelligence, Vol. 20, No. 21, 1996. 5 Medical Journal of Australia Vol. 164, 1996, pp. 347. 6 Halpin, K. et al. 'Identification of likely natural hosts for equine morbillivirus', Communicable Diseases Intelligence, Vol. 20, No. 22, 1996. 7 Allworth, A. et al. 'A human case of encephalitis due to a lyssavirus recently identified in fruit bats', Communicable Diseases Intelligence, Vol. 20, No. 24, 1996.
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