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Results

Incidence of gastroenteritis

During the 12 months between September 2001 and August 2002, 11.2 per cent (683/6,096) of respondents reported gastroenteritis in the previous month. The overall weighted incidence of gastroenteritis was 0.92 (95% C.I. 0.77-1.06) cases per person per year. This equated to 17.2 (95% C.I. 14.5-19.9) million cases each year. About a third of cases resulted in either the person with gastroenteritis, or a carer of the sick person missing some work. After weighting, this equates to approximately 6.5 million lost days of work due to gastroenteritis annually.

The crude incidence of gastroenteritis was similar in all jurisdictions, except for the Northern Territory where it was markedly higher (Table 1). The survey identified that children reported the highest incidence followed by 20-40-year-old adults. Older persons and teenagers reported less gastroenteritis. The median duration of an episode of illness was two days. Gastroenteritis accounted for about 45 million days of illness each year in Australia.

People with more severe gastroenteritis were more likely to seek treatment. Over 20 per cent of persons with gastroenteritis visited a doctor for treatment and 19 per cent of these persons provided a faecal specimen. After weighting, there were an estimated total of 4.6 million visits to a health facility and 3.7 million visits to a doctor in Australia in one year. About 40 per cent of cases reported taking at least one medication for their illness. Pain killers were the most common medication taken during illness. After weighting, OzFoodNet estimates that 7.0 million persons take at least one medication each year for gastroenteritis, which includes prescription and medications purchased over the counter at pharmacies.

Table 1. Crude incidence of gastroenteritis in Australia, September 2001 to August 2002, by state or territory

Jurisdiction	Number surveyed	Number with gastroenteritis	Crude incidence (%)
New South Wales	1,031	111	10.3
Northern Territory	862	137	16.3
Queensland	825	81	9.6
South Australia	781	91	11.3
Tasmania	843	88	10.2
Victoria	895	91	9.9
Western Australia	859	84	9.8
Total	6,096	683	11.2

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Burden of foodborne disease

Of the 28 potentially foodborne pathogens considered only 20 were considered relevant in Australia. The other eight pathogens either did not cause gastroenteritis, or were not locally acquired or transmitted by food. OzFoodNet estimated that 'known' enteric pathogens cause approximately 5 million cases of gastroenteritis each year in Australia. After considering data for these 'known' pathogens from the literature, outbreaks and expert opinion, it was estimated that the credible interval for the proportion of episodes caused by enteric pathogens in food was between 24 per cent and 40 per cent (mid point 32%). From this, it is conservatively estimated that the number of cases of foodborne illness in Australia in a typical year is between 4-6.9 million cases (mid point 5.4 million cases). Among the 'known' pathogens, pathogenic Escherichia coli, noroviruses, Campylobacter and Salmonella contributed the largest number of cases of foodborne gastroenteritis each year.

Rates of notified infections

In 2002, OzFoodNet sites reported 23,434 notifications of eight diseases that were potentially foodborne. This was a 7.7 per cent increase from the mean of 21,761 notifications for the previous four years. Reports for these eight diseases make up almost a quarter of notifications to the National Notifiable Diseases Surveillance System.¹⁴ A summary of the number and rates of notifications by OzFoodNet sites is shown in Appendix 1.

Salmonella infections

In 2002, OzFoodNet sites reported 7,917 cases of Salmonella infection, which equated to a rate of 40.3 cases per 100,000 population. This rate of notification represented an increase of 9.7 per cent over the mean rate for the previous four years (Figure 1). The rate of Salmonella notification in OzFoodNet sites ranged from 24.8 cases per 100,000 population in Victoria to 166.7 cases per 100,000 population in the Northern Territory.

Figure 1. Notification rates of Salmonella infections for 2002 compared to mean rates for 1998-2001, by OzFoodNet site



Overall, notification rates of salmonellosis for 2002 were increased in the Hunter (62.2%), New South Wales (32.7%), Tasmania (21.5%), the Australian Capital Territory (15.1%), Queensland (12.4%) and Victoria (6.3%) compared to historical means. There were moderate declines in the notification rate of Salmonella in South Australia (-19.5%), the Northern Territory (-14.1%), and Western Australia (-10.3%).

OzFoodNet sites reported that the ratio of males to females was approximately 1:1, and ranged from 1.3:1 in the Northern Territory to 0.8:1 in the Hunter. The median age of cases ranged between 17and 26 years at all OzFoodNet sites, except for the Northern Territory and Queensland where the median ages were 1 and 7 years respectively. There were no major changes in the median ages of salmonellosis cases from 2001 to 2002.

The highest rate of Salmonella infection was 230.4 cases per 100,000 population in 0-4-year-old males (Figure 2). The rate was highest in this age group for all sites and ranged from 83.4 cases per 100,000 population in Victoria to 1,421.8 cases per 100,000 population in the Northern Territory. Notification rates were elevated in the 5-9 year age group in all jurisdictions. In all jurisdictions there was also a secondary peak in notification rates in the 20-29 year age range for males and females, which was particularly noticeable in Tasmania.

Top of pageFigure 2. Age specific notification rates of salmonellosis, Australia, 2002



Rates of salmonellosis were highest in northern areas of Australia, with the highest rate in the Kimberley region.^9,14 Western Australia reported that the Kimberley region had a rate of 332 cases per 100,000 population, which was a 40 per cent decline from the rate reported in 2001. Thirty-nine per cent (128/330) of Salmonella notifications in the Northern Territory were in persons of Aboriginal or Torres Strait Island origin. OzFoodNet sites reported that notification rates of salmonellosis increased from south to north along the eastern seaboard of Australia (Figure 3).

Figure 3. Rates of Salmonella notifications in selected regions of eastern Australia, 2002, by date of notification



Notifications were analysed by date of receipt at the health department. Rates were directly standardised to the Australian Bureau of Statistics estimated resident population for Australia in 2002. Estimated resident populations for Queensland were from the Australian Bureau of Statistics 2001 Australian Census.

During 2002, there were 704 notifications of Salmonella Typhimurium 135 (including 135a) to OzFoodNet sites making it the most common infection (Table 2). This compared to 636 notifications of this phage type last year. There were 604 notifications of S. Typhimurium 9, which has been a common phage type for many years. In 2002, Western Australia experienced a significant increase of S. Typhimurium 9 and had the highest total number of notifications for this phage type for all jurisdictions. S. Typhimurium 126 continued to emerge as a significant new phage type around Australia, which followed a large outbreak in South Australia in 2001. S. Typhimurium 170 also continued to increase in Queensland, New South Wales and Victoria. In 2002, there was a significant decrease in numbers of S. Typhimurium 64 from previous years. There were 382 cases of S. Saintpaul, making it the most common Salmonella serovar following S. Typhimurium.

Certain Salmonella serovars traditionally occupy localised niches in specific geographical areas in Australia. During 2002, Salmonella Birkenhead was the third and fourth most common serovar in Queensland and New South Wales respectively. This elevated notification rate reflects an endemic focus of Salmonella Birkenhead in northern New South Wales and south-eastern Queensland. In Tasmania, S. Mississippi, which is rarely reported elsewhere in Australia, made up 48 per cent (79/165) of Salmonella notifications. The notification rate for S. Mississippi in Tasmania was 16.7 notifications per 100,000 population. Similarly, in the Northern Territory, S. Ball made up 14.8 per cent of Salmonella notifications with a rate of 24.7 cases per 100,000 population. This was the highest specific rate for a Salmonella subtype in any OzFoodNet site.

In total, OzFoodNet sites conducted 75 investigations into clusters and point source outbreaks of salmonellosis during 2002. A source of infection was identified for 40 per cent (30/75) of these investigations.

Top of pageTable 2. Numbers, rates and proportions of the top 10 Salmonella infections, 2001 to 2002, by OzFoodNet site*

OzFoodNet site	Salmonella type (serovar/phage type)	Top 10 infections
		2002 n	2002 rate†	Proportion %‡	2001 n	2001 rate	Ratio§
Australian Capital Territory	Typhimurium 9	17	5.3	17.7	10	3.2	1.7
	Typhimurium 135	9	2.8	9.4	2	0.6	4.5
	Typhimurium 197	7	2.2	7.3	0	0.0	-
	Bovismorbificans 24	6	1.9	6.3	0	0.0	-
	Potsdam	4	1.2	4.2	0	0.0	-
	Typhimurium 170	4	1.2	4.2	0	0.0	-
	Typhimurium U290	3	0.9	3.1	0	0.0	-
	Typhimurium 64	3	0.9	3.1	2	0.6	1.5
	Stanley	3	0.9	3.1	5	1.6	0.6
	Adelaide	3	0.9	3.1	0	0.0	-
Hunter	Montevideo	22	4.0	12.3	1	0.2	22.0
	Typhimurium 9	14	2.6	7.8	3	0.6	4.7
	Typhimurium 135	13	2.4	7.3	15	2.8	0.9
	Agona	9	1.7	5.0	1	0.2	9.0
	Potsdam	9	1.7	5.0	2	0.4	4.5
	Typhimurium U290	8	1.5	4.5	3	0.6	2.7
	Typhimurium 170	7	1.3	3.9	6	1.1	1.2
	Virchow 34	5	0.9	2.8	0	0.0	-
	Typhimurium 64	5	0.9	2.8	9	1.7	0.6
	Chester	4	0.7	2.2	1	0.2	4.0
	Javiana	4	0.7	2.2	0	0.0	-
	Singapore	4	0.7	2.2	0	0.0	-
	Typhimurium 195	4	0.7	2.2	0	0.0	-
	Typhimurium 197	4	0.7	2.2	0	0.0	-
	Typhimurium U307	4	0.7	2.2	0	0	-
New South Wales	Typhimurium 9	262	3.9	12.2	132	2.0	2.0
	Typhimurium 135	196	3.0	9.1	201	3.1	1.0
	Typhimurium 170	151	2.3	7.0	35	0.5	4.3
	Birkenhead	89	1.3	4.1	89	1.4	1.0
	Typhimurium 126	64	1.0	3.0	97	1.5	0.7
	Typhimurium 197	61	0.9	2.8	1	0.0	61.0
	Montevideo	59	0.9	2.7	4	0.1	14.8
	Bovismorbificans 24	55	0.8	2.6	1	0.0	55.0
	Typhimurium 135a	50	0.8	2.3	41	0.6	1.2
	Potsdam	44	0.7	2.0	10	0.2	4.4
Northern Territory	Ball	49	24.7	14.9	30	15.2	1.6
	Saintpaul	18	9.1	5.5	17	8.6	1.1
	Chester	17	8.6	5.2	12	6.1	1.4
	Litchfield	16	8.1	4.9	8	4.0	2.0
	Anatum	13	6.6	4.0	9	4.6	1.4
	Muenchen	12	6.1	3.6	19	9.6	0.6
	Typhimurium 135	9	4.5	2.7	9	4.6	1.0
	Agona	6	3.0	1.8	0	0.0	-
	Hvittingfoss	6	3.0	1.8	1	0.5	6.0
	Reading	6	3.0	1.8	6	3.0	1.0
Queensland	Virchow 8	279	7.5	10.2	183	5.0	1.5
	Saintpaul	227	6.1	8.3	173	4.8	1.3
	Birkenhead	136	3.7	5.0	134	3.7	1.0
	Typhimurium 170	138	3.7	5.1	20	0.6	6.9
	Hvittingfoss	114	3.1	4.2	53	1.5	2.2
	Aberdeen	112	3.0	4.1	81	2.2	1.4
	Typhimurium 135	110	3.0	4.0	143	3.9	0.8
	Chester	84	2.3	3.1	68	1.9	1.2
	Typhimurium 9	80	2.2	2.9	50	1.4	1.6
	Waycross	68	1.8	2.5	34	0.9	2.0
South Australia	Typhimurium 8	56	3.7	13.6	3	0.2	18.7
	Typhimurium 126	40	2.6	9.7	110	7.3	0.4
	Typhimurium 99	26	1.7	6.3	4	0.3	6.5
	Typhimurium 108	25	1.6	6.1	31	2.1	0.8
	Typhimurium 9	24	1.6	5.8	49	3.3	0.5
	Typhimurium 145	19	1.2	4.6	0	0.0	-
	Typhimurium 126	17	1.1	4.1	15	1.0	1.1
	Typhimurium 12a	15	1.0	3.6	12	0.8	1.3
	Typhimurium 135a	15	1.0	3.6	13	0.9	1.2
	Typhimurium 135	13	0.9	3.2	24	1.6	0.5
Tasmania	Mississippi	79	16.7	47.9	98	20.8	0.8
	Typhimurium 135	20	4.2	12.1	5	1.1	4.0
	Potsdam	14	3.0	8.5	0	0.0	-
	Typhimurium 9	11	2.3	6.7	11	2.3	1.0
	Typhimurium 126	4	0.8	2.4	1	0.2	4.0
	SaintPaul	3	0.6	1.8	2	0.4	1.5
	Newport	3	0.6	1.8	1	0.2	3.0
	Muenchen	3	0.6	1.8	1	0.2	3.0
	Agona	2	0.4	1.2	2	0.4	1.0
	Niarembe	2	0.4	1.2	0	0.0	-
	Typhimurium 197	2	0.4	1.2	0	0.0	-
	Typhimurium U290	2	0.4	1.2	1	0.2	2.0
Victoria	Typhimurium 135	177	3.6	21.2	92	1.9	1.9
	Typhimurium 170	162	3.3	19.4	72	1.5	2.3
	Typhimurium 9	152	3.1	18.2	127	2.6	1.2
	Typhimurium 126	61	1.3	7.3	16	0.3	3.8
	Saintpaul	43	0.9	5.2	10	0.2	4.3
	Typhimurium U290	39	0.8	4.7	4	0.1	9.8
	Typhimurium 4	21	0.4	2.5	80	1.7	0.3
	Infantis	21	0.4	2.5	27	0.6	0.8
	Potsdam	19	0.4	2.3	8	0.2	2.4
	Aberdeen	15	0.3	1.8	3	0.1	5.0
	Enteritidis 4b	15	0.3	1.2	2	0.0	7.5
Western Australia	Typhimurium 135	65	3.4	8.9	89	4.7	0.7
	Typhimurium 9	45	2.3	6.2	18	0.9	2.5
	Saintpaul	42	2.2	5.8	45	2.4	0.9
	Chester	34	1.8	4.7	31	1.6	1.1
	Enteritidis 4b	28	1.5	3.8	3	0.2	9.3
	Muenchen	27	1.4	3.7	26	1.4	1.0
	Typhimurium 135a	27	1.4	3.7	17	0.9	1.6
	Typhimurium 141	20	1.0	2.7	9	0.5	2.2
	Anatum	18	0.9	2.5	15	0.8	1.2
	Typhimurium U290	14	0.7	1.9	4	0.2	3.5
	Senftenberg	14	0.7	1.9	15	0.8	0.9

* Where there were multiple tenth ranking Salmonella types all data have been shown, giving more than 10 categories for some sites.
† Rate per 100,000 population.
‡ Proportion of total Salmonella notified for this jurisdiction in 2002.
§ Ratio of the number of reported cases in 2002 compared to the number reported in 2001.

This article was published in Communicable Diseases Intelligence Volume 27, No 2, June 2003.