Gastrointestinal diseases

Gastrointestinal diseases are an important cause of illness in Australia. However, data from the NNDSS are likely to underestimate the incidence of disease caused by gastrointestinal pathogens. A number of diseases such as cryptosporidiosis are not nationally notifiable while haemolytic uraemic syndrome (HUS) and infections with Shiga-like toxin (verotoxin) producing E. coli (SLTEC/VTEC) did not become nationally notifiable until late 1998. In addition, only a small proportion of cases come to the attention of physicians, and diagnostic tests to establish an aetiology are only used in a small proportion of these. Moreover, current laboratory testing protocols may not include tests for all significant gastrointestinal pathogens (for example not all laboratories routinely test for Yersinia species) or the tests may not have sufficient sensitivity.

Botulism

There were no cases of botulism reported in 1997. There have been no notifications of this disease reported since the NNDSS began in its present form in 1991.

Campylobacteriosis

There were 11,848 cases of campylobacteriosis reported in 1997, a 2.5 per cent decrease from the number reported for 1996. The rate of notification of campylobacteriosis rose steadily from 1992 to 1996 (Table 3). In 1997, it had the highest annual adjusted rate of notification (100.4 per 100,000 population) for any notified disease, with the exception of hepatitis C (unspecified). In New South Wales, campylobacteriosis was only notifiable as 'foodborne disease in two or more related cases' or 'gastroenteritis in an institution' and therefore was not included for this State.

Campylobacteriosis was reported from all jurisdictions where it was notifiable. Notifications were quite high throughout the year, although higher in the warmer months (October through February) (Figure 3). The highest rate was reported in South Australia, 131 cases per 100,000 population (Map 3). Overall the male:female ratio was 1.2:1. The highest rates of notification were seen in the 0 to 4 years age group (males 227 per 100,000 and females 166 per 100,000 population).

Map 3. Notification rate of campylobacteriosis, 1997, by Statistical Division of residence

Figure 3. Notifications of campylobacteriosis, 1993-1997, by month of onset

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Hepatitis A

There were 3,076 notifications of hepatitis A infection during 1997, a 30 per cent increase on 1996 and a rate of 16.6 per 100,000 population; both number and rate are the highest in the NNDSS since it started in 1991. Although the largest number of reports was from New South Wales (1,455), the highest notification rates were seen in the Northern Territory (49.2 per 100,000 population).

There has been no apparent seasonal distribution for hepatitis A infection notifications in recent years, although in 1997 a very high number were reported in February as a result of the outbreak associated with the consumption of oysters from Wallis Lake (Figure 4). The male:female ratio was 1.5:1. Age group specific notification rates were highest for males aged 20 to 39 years (Figure 5).

Figure 4. Notifications of hepatitis A, 1993-1997, by month of onset

Figure 5. Notification rate of hepatitis A, 1997, by age group and sex

Listeriosis

There were 71 notifications for listeriosis in 1997, which is similar to that in previous years. The Australian Capital Territory and the Northern Territory had no reports. The notification rate was 0.4 per 100,000 population which is consistent with the rates for the period 1992 to 1996.

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Salmonellosis - not elsewhere classified

A total of 7,004 cases of salmonellosis (not elsewhere classified) was reported in 1997, an increase of 17 per cent compared with 1996. The annual notification rate of 37.8 per 100,000 population being the highest for the NNDSS since 1991 (Table 3). Disproportionately high rates, over 100 cases per 100,000 population, were reported for residents of the Northern Territory and parts of Western Australia and Queensland (Map 4).

As in previous years, a seasonal trend was noted, with a higher number of notifications reported with month of onset in the warmer months, November through April (Figure 6). A large peak in notifications early in the year was related to five outbreaks in Victoria caused by five separate serovars.¹⁶ The highest rates of notification were seen in the 0 to 4 years age group (males 200 and females 180 per 100,000 population respectively) (Figure 7).

Map 4. Notification rate of salmonellosis, 1997, by Statistical Division of residence

Figure 6. Notifications of salmonellosis, 1993-1997, by month of onset

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Figure 7. Notification rate of salmonellosis, 1997, by age group and sex

Shigellosis

Shigellosis was notified for 799 persons in 1997, 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, 4.3 per 100,000 population, was less than the rates for each of the years 1992 to 1996. The highest rate was seen for residents of the Northern Territory (90 per 100,000 population).

Notifications were slightly higher in the first four months of the year, reflecting the expected higher numbers in warmer months (Figure 8). The highest age group specific numbers and rates occurred in the 0 to 4 years age group for both (males 20.8 and females 18.6 per 100,000 population, respectively) (Figure 9).

Figure 8. Notifications of shigellosis, 1993-1997, by month of onset

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Figure 9. Notification rate of shigellosis, 1997, by age group and sex

Typhoid and paratyphoid

There were 77 cases of typhoid and paratyphoid notified in 1997, the notification rate being 0.4 per 100,000 population. All States and Territories provided notifications and there was no apparent seasonal trend.

Yersiniosis

There were 245 notifications for yersiniosis in 1997, 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'. Reports of yersiniosis have steadily decreased since 1992. The majority of reports were received from Queensland and South Australia (Table 1).

The male:female ratio was 1.4:1. The highest age group specific numbers and rates occurred in the 0 to 4 years age group for both males and females (Figure 10) with 27 per cent of all cases notified being in this age group. Slightly higher numbers were reported in the first three months of the year compared with later months (Figure 11).

Figure 8. Notifications of shigellosis, 1993-1997, by month of onset

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Figure 9. Notification rate of shigellosis, 1997, by age group and sex

Discussion

Campylobacteriosis and non-typhoidal salmonellosis are the predominant enteric pathogens reported to the NNDSS. These trends are similar to those recorded in other developed countries such as the United States of America and the United Kingdom.¹⁷ In the case of salmonellosis, however, Australia differs, as we have not yet seen widespread disease due to Salmonella enteritidis. This pathogen is the main cause of foodborne disease in North America and parts of Europe, with hens' eggs the main source of human infection.

The continued huge numbers of notifications of campylobacteriosis is of considerable public health concern. More knowledge is needed on the epidemiology of this disease to help determine the major sources of, and risk factors for, the transmission of Campylobacter species. Public health interventions may then be developed to reduce the incidence of disease.

Of the remaining enteric pathogens described in this report, transmission is thought to be mainly via food for Salmonella, Listeria and Yersinia species. However, hepatitis A virus and Shigella species are often spread from one person to another.¹⁸ With the exception of hepatitis A infection, shigellosis and salmonellosis, notifications have either remained steady (campylobacteriosis and listeriosis) or have decreased (yersiniosis) in recent years. Outbreaks of hepatitis A in young homosexual men due to person-to-person transmission frequently occur, and the age and sex distribution of the reported cases during 1997 suggest that such outbreaks occurred during 1997. The oyster-associated outbreak of hepatitis A infection centred in the Wallis Lake region of New South Wales in 1997¹⁹ however, is a reminder that this and other potential foodborne pathogens may cause large and widespread disease outbreaks if food safety measures are inadequate.

This article {extract} was published in Communicable Diseases Intelligence Vol 23 Number , 21 January 1999 and may be downloaded as a full version PDF from the Table of contents page. Volume 23 1999.