This article {extract} was published in Communicable Diseases Intelligence Volume 23 Number 11 - 28 October 1999 and may be downloaded as a full version PDF from the Table of contents page.

Results continued

Gastrointestinal diseases

Enteric infections are a major cause of illness in Australia. Surveillance of enteric infections in Australia is likely to underestimate the incidence of enteric infections for several reasons. Some diseases are not nationally notifiable, such as cryptosporidiosis, or did not become nationally notifiable until late 1998, such as haemolytic uraemic syndrome (HUS) and infections with Shiga-like toxin (verotoxin) producing E. coli (SLTEC/VTEC). Only a small proportion of cases present to physicians, and diagnostic tests are only conducted on a proportion of cases. Furthermore, current routine laboratory testing protocols may not include tests for all significant enteric pathogens (for example not all laboratories routinely test for Yersinia species). Together these factors impinge on the sensitivity of the existing surveillance system for enteric pathogens.

Botulism

There was one case of botulism reported in 1998 in South Australia (Table 1). This represents the first notification of this disease reported since the NNDSS began in its present form in 1991.

Campylobacteriosis

There were 13,439 cases of campylobacteriosis reported in 1998 (Table 1), continuing the previous trend of a steady increase in the number of notifications of campylobacteriosis from 1992 to 1997. The rate of notification in 1998 was 108.3 per 100,000 population, the highest rate for all notifiable infections in 1998. The highest rate by State/Territory continued to be reported in South Australia, with 153.6 cases per 100,000 population (Table   2). New South Wales was excluded from the analysis as campylobacteriosis was reported as 'foodborne disease in two or more related cases' or 'gastroenteritis in an institution'.

Campylobacteriosis was reported from all jurisdictions where it was notifiable. The highest notification rates (160+ per 100,000 population) were seen in the Statistical Divisions of South West in Queensland, Kimberley in West Australia, and Eyre and Yorke and Lower North in South Australia (Map 2).

Map 2. Notification rate of campylobacteriosis, 1998, by Statistical Division of residence



The number of notifications remained high throughout the year and was highest in the warmer months (January, February and October to December) with a large peak at the end of 1998 (Figure 3). Overall the male to female ratio was 1.1:1. The distribution of notifications was bimodal with a high peak in the 0-4 years age group and a rise in the 20-29 years age groups. The highest rate of notification was seen in the 0-4 year age group (males 377 per 100,000 and females 304 per 100,000 population) (Figure 4).
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Figure 3. Notifications of campylobacteriosis, 1991-1998, by month of onset



Figure 4. Notification rate of campylobacteriosis, 1998, by age group and sex

Hepatitis A

There were 2,503 notifications of hepatitis A infection during 1998 (Table 1); a 19% decrease from 1997, and a rate of 13.4 per 100,000 population. The largest number of reports were from Queensland (1042) and NSW (945) (Table 1). The highest notification rates were from Queensland (30.1 per 100,000 population) and the Northern Territory (24.7 per 100,000 population) (Table 2). The notification rate for the Northern Territory had decreased compared with 49.2 per 100,000 population reported in 1997.

Hepatitis A was notifiable and reported in all jurisdictions. By Statistical Divisions the highest rate of notifications (70+ per 100,000 population) was in Far North and Fitzroy in Queensland (Map 3).

Map 3. Notification rate of hepatitis A, 1998, by Statistical Division of residence



No apparent seasonal distribution for hepatitis A infection notifications has been reported in recent years, although in 1998 a higher number of reports were received early in the year (Figure 5). The male to female ratio was 1.6:1; similar to the previous years. Age group specific notification rates were bimodal with peaks in the 5-9 years and 20-29 years age groups; the highest notification rate for males was for those aged 25-29 years and for females was for those aged 5-9 years (Figure 6).

Figure 5. Notifications of hepatitis A, 1991-1998, by month of onset



Figure 6. Notification rate of hepatitis A, 1998, by age group and sex


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Listeriosis

There were 58 notifications for listeriosis in 1998 (Table 1), similar to previous years. The Northern Territory was the only State or Territory with no reports. The notification rate was 0.3 per 100,000 population (Table 2), lower than 1997 but consistent with the rates for the period 1992 to 1997.

Salmonellosis - not elsewhere classified

A total of 7,700 cases of salmonellosis (not elsewhere classified) were reported in 1998 (Table 1). The annual notification rate of 41.1 per 100,000 population (Table 2) was the highest level for the NNDSS since 1991. The highest rate was reported in the Northern Territory, 215.8   per 100,000 more than twice the notification rates for the States and other Territory (Table 2).

Salmonellosis was notifiable and reported from all jurisdictions. By Statistical Division the highest rate of notification (300+ per 100,000 population) was in Kimberley in Western Australia (Map 4).

As in previous years, a seasonal trend was noted, with a higher number of notifications reported in the warmer months, January through April and November and December (Figure 7). The highest rates of notification were seen in the 0-4 years age group for both males and females (males 249.9 and females 221.2 per 100,000 population respectively) (Figure 8). The overall ratio of males to females was 1.1:1.

Figure 7. Notifications of salmonellosis, 1991-1998, by month of onset



Figure 8. Notification rate of salmonellosis, 1998, by age group and sex



Map 4. Notification rate of salmonellosis, 1998, by Statistical Division of residence

Shigellosis

Shigellosis was notified for 615 cases in 1998 (Table 1), from all States and Territories except New South Wales, where it was only notifiable as 'foodborne disease in two or more related cases' or 'gastroenteritis in an institution'. The notification rate, 5 per 100,000 population, was greater than the rate in 1997 (Table 2). The highest rate was seen in the Northern Territory (51.6 per 100,000 population) (Table 2).

Notifications did not show the same peak in the first four months of the year, that was noted in previous years (Figure 9). There was a bimodal distribution of notifications with peaks in the 0-4 years and 20-24 years age groups. The highest age group specific rates occurred in the 0-4   years age group for both males and females (males   18.1 and females 21.3 per 100,000 population, respectively) (Figure 10). The overall male to female ratio was 1.1:1.
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Figure 9. Notifications of shigellosis, 1991-1998, by month of onset



Figure 10. Notification rate of shigellosis, 1998, by age group and sex

Typhoid and paratyphoid

There were 69 cases of typhoid and paratyphoid notified in 1998 (Table 1), and the notification rate was 0.4 per 100,000 population; unchanged from 1997 (Table 3). The Australian Capital Territory was the only State or Territory with no reports (Table 1). The highest rate was in the Northern Territory (Table 2). There was a peak early in the year as in previous years (Figure 11). The highest rates of notification were for males in the 15-29 years age groups and another peak in those aged 85+ years (1.4 per 100,000 population) and for females aged 20-24 years (0.7   per 100,000 population respectively) (Figure 12). The overall male to female ratio was 2:1.

Figure 11. Notifications of typhoid, 1991-1998, by month of onset



Figure 12. Notification rate of typhoid, 1998, by age group and sex

Yersiniosis

There were 207 notifications of yersiniosis in 1998 (Table   1), from all States and Territories except New South Wales, where it was only notifiable as 'foodborne disease in two or more related cases' or 'gastroenteritis in an institution'. The number of reports of yersiniosis has continued to decrease. The greatest number of reports and the highest notification rate were both from Queensland (Table 1 and Table 2).

Slightly higher numbers were reported early in the year following the same pattern of previous years (Figure 13). The overall male to female ratio was 1.7:1. The highest age group specific rates occurred in the 0-4 years age group for both males and females (Figure 14).
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Figure 13. Notifications of yersiniosis, 1991-1998, by month of onset



Figure 14. Notification rate of yersiniosis, 1998, by age group and sex

Discussion

Campylobacteriosis and non-typhoidal salmonellosis continued to be the predominant enteric pathogens reported to the NNDSS, similar to the pattern reported in the United States of America and the United Kingdom.¹⁷

Unlike salmonellosis the high rates of campylobacteriosis are not limited to northern Australia. Notifications of campylobacteriosis increased in 1998 compared with 1997. One outbreak of campylobacteriosis was confirmed to be a water-borne infection (CDNANZ personal communication). The increase in campylobacteriosis in Australia was also seen in New Zealand late in 1998, where the rates increased by 30% from the previous year (CDNANZ personal communication). Investigations of outbreaks of campylobacteriosis and identification of risk factors for acquisition of infection remain important if the burden of disease is to decrease.

The incidence of salmonellosis also increased in 1998; a steady rise has been occurring since 1994. Some of the increase may be the result of improved surveillance. Outbreaks of Salmonella oranienburg from contaminated gelati and Salmonella RDNC A045 in a wedding party were reported in CDI.^18,19 Other outbreaks in 1998 included Salmonella chester, Salmonella Typhimurium PT 64 associated with spiced sausages, and Salmonella virchow (CDNANZ personal communication).

The number of notifications of listeriosis was similar and the number of notifications of hepatitis A and yersiniosis decreased in 1998. The decrease in hepatitis A notifications may reflect a correction to the 1997 figures that included the Wallis Lake outbreak. Small outbreaks of hepatitis A in 1998 were reported in select population groups; intravenous drug users, homosexual men, indigenous communities and people linked to child-care centres. These identified subgroups may be associated with some factors that can be addressed to further reduce morbidity.^20,21 (CDNANZ personal communication; March, April, June, October and November 1998).

The peak in notifications for typhoid in males aged more than 85 years was due to one case occurring in a small population.