Results - Salmonella

Rates of notified infections

In 2004, OzFoodNet sites reported 24,313 notifications of eight potentially foodborne diseases. This was a 9.0 per cent increase from the mean of 22,289 notifications for the previous six 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 2004, OzFoodNet sites reported 7,842 cases of Salmonella infection, which equated to a rate of 39.0 cases per 100,000 population. This rate of notifications represented an increase of 4.9 per cent over the mean rate for the previous six years (Figure 1). The rate of Salmonella notification in OzFoodNet sites ranged from 22.9 and 23.2 cases per 100,000 population in the Hunter and Victoria, respectively, to 195.1 cases per 100,000 population in the Northern Territory (Figure 2).

Figure 1. Notifications and annual rates of Salmonella infections, Australia, 1998 to 2004

Figure 2. Notification rates of Salmonella infections for 2004 compared to mean rates for 1998 to 2003, by OzFoodNet site

The notification rates of salmonellosis remained relatively constant over the last seven years. Overall, notification rates of salmonellosis for 2004 were increased in New South Wales (20.3%), the Australian Capital Territory (18.0%) and Queensland (9.9%) compared to historical means. Western Australia (-21.5%), Tasmania (-17.2%) and South Australia (-11.2%) recorded declines in the notification rate of Salmonella, with other jurisdictions recording similar rates to previous years (Figure 2). OzFoodNet sites reported that the ratio of males to females was approximately 1:1.1. The highest age-specific rate of Salmonella infection was 221 cases per 100,000 population in males aged 0–4 years and 204 in females aged 0–4 years. Notification rates were also elevated in the 5–9 year age group with a secondary peak in the 20–29 year age range for males and females.

Rates of salmonellosis were highest in northern areas of Australia. The highest rate in Australia is consistently reported in the Kimberley region of Western Australia.¹⁴ In the Northern Territory, the rate of Salmonella notifications was 283 per 100,000 population in Indigenous people compared to 137 per 100,000 population in non-Indigenous people.

During 2004, there were 629 notifications of Salmonella Typhimurium 170/108 and 585 notifications of S. Typhimurium 135 (including 135a) to OzFoodNet sites making these the most common Salmonella infections (Table 1). S. Typhimurium 170 and S. Typhimurium 108 are the same phage type and continued to emerge as a significant phage type around Australia, accounting for 10 outbreaks of foodborne disease during 2004. S. Typhimurium 197 emerged as a cause of significant disease, particularly in Queensland, where 56 per cent (141/251) of notifications of this phage type were reported. There were 383 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 2004, Salmonella Birkenhead infections were the fourth most common serovar in New South Wales and the fifth most common in Queensland. The total number of cases in these two States (244 cases) was 38 per cent higher in 2004 compared to 2003. This elevated notification rate reflects an endemic focus of S. Birkenhead in northern New South Wales and south-eastern Queensland. In Tasmania, 53 per cent of reported cases of salmonellosis were S. Mississippi infections, equating to a rate of 13.2 cases per 100,000 population. The highest serovar specific rate in Australia was S. Ball in the Northern Territory, with a rate of 25.2 cases per 100,000 population. Reported rates of S. Saintpaul in the Northern Territory were 23.2 cases per 100,000 population.

Salmonella Enteritidis

S. Enteritidis is a serotype that can infect the internal contents of eggs via the oviducts of infected chickens, predominantly with one strain: S. Enteritidis phage type 4. People may become infected with this serotype after eating undercooked eggs. This phage type has caused major problems in the Northern Hemisphere where it has become established in commercial egg laying flocks. Australia is largely free of S. Enteritidis phage type 4 except in people infected overseas. OzFoodNet is currently investigating other phage types of S. Enteritidis that are acquired locally in Australia to determine risk factors for infection.

During 2004, OzFoodNet sites reported 422 cases of Salmonella Enteritidis, which was higher than for 2003. The majority of cases were related to travel overseas (69%) or were of unknown travel history (18%) (Table 2). Relevant travel histories are difficult to obtain, as people have often travelled to several countries before visiting Australia. Asian countries were commonly mentioned, which reflects the frequency of Asia as a travel destination for Australians (Table 3). In the Asian region, cases of S. Enteritidis infection most commonly reported travelling to Bali (38%). Fifteen per cent of people acquiring their infection overseas reported travelling to Europe.

The most common phage types depended on the region that the person travelled to. For people travelling to Bali and Indonesia, the most common phage types were 6a, 5a, 4, and 4b. In Malaysia and Singapore the most common infecting phage types were 1 and 6a, with no phage type 4 reported. Thailand travellers were infected with the same phage types as Malaysian travellers, along with phage type 4. For travellers returning from Europe, phage types 1, 4, 5a and 6 were most common.

Overall, 13 per cent (54/422) of patients infected with S. Enteritidis acquired their infection in Australia (Figure 3). The median age of cases was 31 years (range 0–85 years) and the male to female ratio was 1.2:1. Thirty-six per cent (40/112) of S. Enteritidis infections in Queensland were locally acquired compared to Victoria where only two per cent (2/86) of infections were locally acquired. The majority of locally acquired infections in Queensland were due to phage type 26. There was a temporal clustering of cases of S. Enteritidis in December 2003—March 2004, although no common sources were identified. There were no locally acquired cases of S. Enteritidis in the Australian Capital Territory or Western Australia .

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Salmonella clustering

In total, health departments conducted 81 investigations into clusters and point source outbreaks of salmonellosis during 2004. A source of infection was identified for 44 per cent (36/81) of these investigations.

Table 1. Numbers, rates and proportions of the top 10 Salmonella infections, 2003 to 2004, by OzFoodNet site*

OzFoodNet site	Salmonella type (sero/phage type)	2004			2003
		n	Rate†	Proportion‡ (%)	n	Rate	Ratio§
Australian Capital Territory	Typhimurium 170	31	9.6	31.3	4	1.2	7.8
	Typhimurium 197	7	2.2	7.1	0	0.0	-
	Infantis	6	1.9	6.1	3	0.9	2.0
	Typhimurium 9	6	1.9	6.1	4	1.2	1.5
	Typhimurium 135	5	1.5	5.1	25	7.7	0.2
	Typhimurium 12	4	1.2	4.0	0	0.0	-
	Virchow 8	4	1.2	4.0	0	0.0	-
	Agona	3	0.9	3.0	0	0.0	-
	Chester	2	0.6	2.0	1	0.3	2.0
	Mbandaka	2	0.6	2.0	1	0.3	2.0
	Newport	2	0.6	2.0	0	0.0	-
	Stanley	2	0.6	2.0	0	0.0	-
	Subsp I ser 16:1,v:-	2	0.6	2.0	1	0.3	2.0
	Typhimurium 104L	2	0.6	2.0	2	0.6	1.0
	Typhimurium 12a	2	0.6	2.0	0	0.0	-
	Typhimurium U290	2	0.6	2.0	4	1.2	0.5
Hunter	Typhimurium 170	16	2.9	12.7	10	1.8	1.6
	Typhimurium 135	10	1.8	7.9	1	0.2	10.0
	Typhimurium 12	10	1.8	7.9	0	0.0	-
	Typhimurium 4	8	1.5	6.3	9	1.6	0.9
	Typhimurium 9	5	0.9	4.0	7	1.3	0.7
	Typhimurium U290	5	0.9	4.0	8	1.5	0.6
	Chester	5	0.9	4.0	3	0.5	1.7
	Potsdam	4	0.7	3.2	1	0.2	4.0
	Saintpaul	4	0.7	3.2	2	0.4	2.0
	Birkenhead	4	0.7	3.2	3	0.5	1.3
New South Wales	Typhimurium 170	333	4.9	15.7	232	3.5	1.4
	Typhimurium 12	170	2.5	8.0	38	0.6	4.5
	Typhimurium 135	140	2.1	6.6	135	2.0	1.0
	Typhimurium 9	108	1.6	5.1	131	2.0	0.8
	Birkenhead	77	1.1	3.6	68	1.0	1.1
	Typhimurium 4	66	1.0	3.1	34	0.5	1.9
	Infantis	53	0.8	2.5	86	1.3	0.6
	Typhimurium u290	46	0.7	2.2	30	0.4	1.5
	Typhimurium 197	43	0.6	2.0	66	1.0	0.7
	Virchow 8	40	0.6	1.9	27	0.4	1.5
Northern Territory	Ball	50	25.0	13.1	44	22.2	1.1
	Saintpaul	47	23.5	12.3	28	14.1	1.7
	Litchfield	15	7.5	3.9	9	4.5	1.7
	Muenchen	14	7.0	3.7	14	7.1	1.0
	Havana	13	6.5	3.4	11	5.5	1.2
	Anatum	12	6.0	3.1	22	11.1	0.5
	Chester	12	6.0	3.1	16	8.1	0.8
	Senftenberg	8	4.0	2.1	7	3.5	1.1
	Wandsworth	8	4.0	2.1	3	1.5	2.7
	Weltevreden	8	4.0	2.1	10	5.0	0.8
Queensland	Virchow 8	241	6.2	8.6	165	4.3	1.5
	Saintpaul	223	5.7	8.0	167	4.4	1.3
	Typhimurium 135	176	4.5	6.3	155	4.1	1.1
	Birkenhead	163	4.2	5.8	109	2.9	1.5
	Typhimurium 197	141	3.6	5.0	90	2.4	1.6
	Aberdeen	114	2.9	4.1	75	2.0	1.5
	Hvittingfoss	110	2.8	3.9	72	1.9	1.5
	Waycross	94	2.4	3.4	50	1.3	1.9
	Chester	84	2.2	3.0	98	2.6	0.9
	Typhimurium 12a	53	1.4	1.9	1	0.0	53.0
South Australia	Typhimurium 108	70	4.6	13.4	32	2.1	2.2
	Typhimurium 9	46	3.0	8.8	28	1.8	1.6
	Typhimurium 135a	25	1.6	4.8	18	1.2	1.4
	Chester	21	1.4	4.0	24	1.6	0.9
	Typhimurium RDNC	20	1.3	3.8	12	0.8	1.7
	Typhimurium 135	19	1.2	3.6	17	1.1	1.1
	Infantis	17	1.1	3.2	20	1.3	0.9
	Singapore	17	1.1	3.2	9	0.6	1.9
	Typhimurium 8	17	1.1	3.2	2	0.1	8.5
	Typhimurium 126 var	17	1.1	3.2	0	0.0	-
Tasmania	Mississippi	63	13.1	52.5	70	14.7	0.9
	Typhimurium 9	4	0.8	3.3	7	1.5	0.6
	Typhimurium 12a	4	0.8	3.3	3	0.6	1.3
	Typhimurium 170	3	0.6	2.5	5	1.0	0.6
	Enteritidis 4b	2	0.4	1.7	0	0.0	-
	Enteritidis 6a	2	0.4	1.7	1	0.2	2.0
	Newport	2	0.4	1.7	2	0.4	1.0
	Paratyphi B bv Java Dundee	2	0.4	1.7	1	0.2	2.0
	Potsdam	2	0.4	1.7	0	0.0	-
	Saintpaul	2	0.4	1.7	5	1.0	0.4
	Typhimurium 135	2	0.4	1.7	6	1.3	0.3
	Typhimurium 141	2	0.4	1.7	0	0.0	-
	Typhimurium RDNC	2	0.4	1.7	0	0.0	-
	Virchow 6	2	0.4	1.7	0	0.0	-
Victoria	Typhimurium 9	145	2.9	12.8	159	3.2	0.9
	Typhimurium 170	137	2.8	12.1	125	2.5	1.1
	Typhimurium 135	88	1.8	7.8	233	4.7	0.4
	Typhimurium 197	59	1.2	5.2	21	0.4	2.8
	Infantis	43	0.9	3.8	54	1.1	0.8
	Typhimurium u290	36	0.7	3.2	88	1.8	0.4
	Typhimurium 126	28	0.6	2.5	18	0.4	1.6
	Virchow 8	26	0.5	2.3	9	0.2	2.9
	Typhimurium 12	23	0.5	2.0	19	0.4	1.2
	Stanley	21	0.4	1.9	19	0.4	1.1
	Typhimurium RDNC	21	0.4	1.9	11	0.2	1.9
Western Australia	Saintpaul	46	2.3	7.5	29	1.5	1.6
	Typhimurium 135a	45	2.3	7.3	42	2.2	1.1
	Typhimurium 135	29	1.5	4.7	30	1.5	1.0
	Chester	24	1.2	3.9	36	1.8	0.7
	Muenchen	23	1.2	3.7	28	1.4	0.8
	Enteritidis 6a	21	1.1	3.4	8	0.4	2.6
	Stanley	14	0.7	2.3	7	0.4	2.0
	Havana	13	0.7	2.1	10	0.5	1.3
	Senftenberg	13	0.7	2.1	15	0.8	0.9
	Typhimurium 9	13	0.7	2.1	20	1.0	0.7

* 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 2004.

§ Ratio of the number of reported cases in 2004 compared to the number reported in 2003.

RDNC = 'Reactive but Does Not Conform' and represents phage type patterns that are not yet assigned.

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Table 2. Numbers of Salmonella Enteritidis infections acquired overseas and in Australia in 2004, by OzFoodNet site

OzFoodNet site	Overseas travel			Total
	Yes	No	Unknown
Australian Capital Territory	2	0	0	2
New South Wales	43	4	50	97
Northern Territory	1	2	2	5
Queensland	51	40	21	112
South Australia	27	5	0	32
Tasmania	8	1	0	9
Victoria	84	2	0	86
Western Australia	77	0	2	79
Total	293	54	75	422

Table 3. Numbers of Salmonella Enteritidis infections acquired overseas, 2004, by region of travel

Region of travel	Number of cases	Percentage
Africa	5	1.7
America	1	0.3
America/Europe	1	0.3
Asia/Americas	1	0.3
Asia/Europe	15	5.1
Asia -other	6	2.1
Bali	112	38.2
China	9	3.1
Europe	29	9.9
Hong Kong	9	3.1
Indian subcontinent	8	2.7
Indonesia	16	5.5
Malaysia	19	6.5
Middle East	8	2.7
Mixed Asia	9	3.1
Pacific	4	1.4
Phillipines	8	2.7
Singapore	16	5.5
Solomons	1	0.3
Thailand	13	4.4
Unknown	3	1.0
Total	293	100

Figure 3. Locally-acquired Salmonella Enteritidis infections, 2003 to 2004, by major phage type and month of notification

RDNC = 'Reactive but Does Not Conform' and represents phage type patterns that are not yet assigned.

 

This article was published in Communicable Diseases Intelligence Vol 29 No 2, June 2005.