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Results continued

Rates of notified infections continued

Campylobacter infections

Data for campylobacteriosis were not available for New South Wales, including the Hunter Health Area. With this exception, in 2002 OzFoodNet sites reported 14,716 cases of Campylobacter infection, which equated to a rate of 113 cases per 100,000 population.² This rate represented a 5.8 per cent increase over the mean for the previous four years (Figure 4). The increase was consistently observed in each quarter of 2002, with the highest rates in spring.

Figure 4. Notification rates of Campylobacter infections for 2002 compared to mean rates for 1998-2001, by site excluding New South Wales



Rates of campylobacteriosis increased in Tasmania (27.1%), Western Australia (10.3%), and South Australia (7.5%). Rates were similar to historical means for Victoria, the Australian Capital Territory and Queensland. The Northern Territory experienced a 9.5 per cent decline from historical reports. Geographically, there was no trend in increasing or decreasing rates of notification of Campylobacter infection with latitude along the eastern seaboard, in contrast to the pattern observed for Salmonella infections (Figure 5). The highest rate of Campylobacter infection was 165.7 notifications per 100,000 population in South Australia and the lowest rate was 101.2 notifications per 100,000 population in Victoria.

Figure 5. Rates of Campylobacter 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.

The overall ratio of male to females was 1.2:1. All sites, except Tasmania, reported a slight predominance of males amongst notified cases, with male to female ratios ranging from 1.1:1 in Queensland to 1.5:1 in the Northern Territory. The median ages of cases ranged from 17 to 30 years. The highest age specific rates were in male children in the 0-4 year age group, with a secondary peak in the 20-29 year age range for males and females (Figure 6). The highest age specific rates were in males in the 0-4 year age group in the Northern Territory (518 cases per 100,000 population) and South Australia (473 cases per 100,000 population). The lowest rates in the 0-4 year age group was in Tasmanian female children (128 cases per 100,000 population).

Top of pageFigure 6. Age specific notification rates of campylobacteriosis, Australia, 2002



There was only one investigation of Campylobacter during 2002 where a source was identified, which occurred in a community-wide increase in Far North Queensland. Thirty-three per cent (68/208) of notified cases in the Northern Territory were in persons of Aboriginal or Torres Strait Island descent.

Listeria

OzFoodNet sites reported 62 cases of listeriosis in 2002, which represents a notification rate of 0.3 cases per 100,000 population (Figure 7). This was a slight increase of 1.2 per cent in the same number of notifications compared to the historical mean. Western Australia (0.6 cases per 100,000 population) had the highest notification rate amongst OzFoodNet sites, which was followed by Queensland (0.5 cases per 100,000 population). There were no common source outbreaks of listeriosis detected during the period, although sites investigated several instances of temporal clustering of cases identified using Pulsed Field Gel Electrophoresis (PFGE).

Figure 7. Notification rates of Listeria infections for 2002 compared to mean rates for 1998-2001, by OzFoodNet site



Ninety-seven per cent (60/62) of infections during 2002 were reported in persons who were either elderly and/or immunocompromised. More cases among females were notified during 2002, with the male to female ratio being 0.8:1. OzFoodNet sites reported that the median ages of non-pregnancy associated cases were between 60-86 years. The highest age specific rate of 1.5 cases per 100,000 population was in males over the age of 60 years (Figure 8). There was one notification of listeriosis in a 20-day-old female in Victoria and environmental transmission was suspected. Seventeen per cent (10/60) of non-pregnancy associated cases died.

Figure 8. Age specific notification rates of non-pregnancy associated listeriosis, Australia, 2002



Sites reported two maternal foetal Listeria infections during 2002, which equated to a rate of 0.8 cases per 100,000 births.* The foetus or neonate died in one of these cases. There was a substantial decline in the number of materno-foetal infections in the three years between 2000 and 2002 (Figure 9).

Top of pageFigure 9. Notifications of Listeria showing non-pregnancy related infections and deaths and materno-foetal infections and deaths, Australia, 2000 to 2002

* Births data from the Australian Institute of Health and Welfare National Perinatal Statistics Unit for 1999 and includes live births and foetal deaths.¹⁵

Yersinia

The CDNA agreed to stop reporting notifications of Yersinia infections to the National Notifiable Diseases Surveillance System, as of January 2001. The main reason for this was the apparent decline in incidence and lack of identified outbreaks. In May 2001, the Victorian Government revised regulations governing reporting of infectious diseases, at which time they removed yersiniosis from the list of reportable conditions. Yersinia is also not notifiable in New South Wales. No other Australian jurisdictions have amended their legislation to remove yersiniosis from lists of reportable conditions.

In 2002, OzFoodNet sites reported 99 cases of yersiniosis, which equated to a rate of 1.2 notifications per 100,000 population (Figure 10). The overall rate declined 15.1 per cent from previous years, when adjusted for the absence of reporting from Victoria and New South Wales. The Northern Territory recorded seven cases of yersiniosis during 2002, giving a rate of 3.0 cases per 100,000 population. This was the highest rate nationally and considerably higher than historical levels in this jurisdiction. The reasons for the increase were unclear, although laboratory practices in the Territory did not change during 2002 (personal communication Gary Lum, Royal Darwin Hospital, 21 May 2003).

Figure 10. Notification rates of Yersinia infections for 2002 compared to mean rates for 1998-2001, Australia excluding Victoria and New South Wales, by OzFoodNet site



Queensland reported 74 per cent (73/99) of all cases, which equated to a rate of 2.0 cases per 100,000 population. The rates of yersiniosis were similar in all three Queensland health zones, and ranged from 1.6 to 2.5 notified cases per 100,000 population.

Overall there was a predominance of notifications in males, with the male to female ratio being 1.4:1. In the two jurisdictions with the majority of cases-South Australia and Queensland-infections in males were more common than in females, with male to female ratios of 2.3:1 and 1.4:1 respectively. Despite this, the highest age specific rate of notification (8.1 cases per 100,000 population) was in females in the 0-4 year age group (Figure 11). The Northern Territory (35.0 cases per 100,000 population) and Queensland (12.5 cases per 100,000 population) reported the highest rates in this age group of females.

Figure 11. Age specific notification rates of Yersinia infections, Australia excluding Victoria and New South Wales, 2002



The decrease in Yersinia notifications has been occurring for several years and has been observed in other countries. They may be due to changes in laboratory testing practices or a true decline in incidence. Despite the low rates of this disease, it is important for health agencies to continue surveillance for yersiniosis due to its potential for foodborne spread and to monitor the effect of zoonotic control programs.

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Shigella

OzFoodNet sites reported 505 cases of shigellosis during 2002, which equated to a notification rate of 2.6 cases per 100,000 population (Figure 12). This was a 38 per cent decrease in the rate of notification compared with historical averages, after adjusting for the introduction of notifications from New South Wales in January 2001.

Figure 12. Notification rates of Shigella infections for 2002 compared to mean rates for 1998-2001, by OzFoodNet site

* Shigellosis became notifiable in New South Wales from 2001 onwards.

The highest rate of notification was in the Northern Territory (52 cases per 100,000 population), which was 20 times higher than the overall Australian rate. Eighty-seven per cent (90/103) of notifications in the Northern Territory were in persons of Aboriginal or Torres Strait Island origin. Only Western Australia observed an increased rate compared to the four years mean, the majority of which was related to an increase in cases in the fourth quarter of 2002 from remote areas of the state.

The male to female ratio of shigellosis cases was 1:1. The highest age specific rates were in males (14.1 cases per 100,000 population) and females (13.9 cases per 100,000 population) in the 0-4 year age group, with secondary smaller peaks in the 25-29 year age group for females and the 35-39 year age group for males (Figure 13). There were no reported outbreaks of shigellosis or confirmed links with food. In Australia, the majority of shigellosis infections are thought to be due to person-to-person transmission, or are acquired overseas.

Figure 13. Age specific notification rates of shigellosis, Australia, 2002



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Typhoid

OzFoodNet sites reported 64 cases of typhoid infection during 2001, equating to an overall notification rate of 0.3 cases per 100,000 population (Figure 14). The number of notifications was similar to previous years. The highest rate was reported in Victoria (0.4 cases per 100,000 population). Tasmania, the Northern Territory and the Hunter sites did not report any cases.

Figure 14. Notification rates of typhoid infections for 2002 compared to mean rates for 1998-2001, by OzFoodNet site



Where travel status was known, sites reported that 95 per cent (54/57) of cases of typhoid had recently travelled overseas (Table 3). Thirty-seven per cent (20/54) of these cases had recently travelled from Indonesia or Bali and the predominant phage types were D2 (6 cases) and E2 (4 cases). Nineteen cases had travelled to India or the subcontinent and the predominant phage type of S. Typhi was E1a (12 cases). The three non-travelling cases were either long-term carriers or infected by close contact with a known carrier. Travel status was unknown for seven cases. Information on phage type was reported for 66 per cent (42/64) of isolates.

Table 3. Travel status for typhoid cases, Australia, 2002

Country	Number of cases	Predominant phage types*
Indonesia	18	E2 (4), D2 (5)
Syria/Lebanon	2
India	9	E1a (7)
Papua New Guinea	6	E4 (1), D2 (4)
Bangladesh	5	E1a (2)
Pakistan	5	E1a (3)
Kenya/Sudan	2	A (2)
Bali	2	D2 (1)
Samoa	1	E1a (1)
Philippines	1
Malaysia	1	E4 (1)
Italy	1
Carrier	1
Infected by carrier	2
Travel on ship to high risk areas	1
Unknown	7
Total	64

* Numbers in parentheses represent number of cases infected by the phage type. Note that other phage types may have caused disease in returned travellers but are not shown here.

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Shiga toxin producing E. coli infections

OzFoodNet sites reported 58 cases of shiga toxin producing E. coli (STEC) infection during 2002 (Figure 15). This number does not include cases of haemolytic uraemic syndrome where a toxigenic E. coli was isolated. The notification rate of 0.3 cases per 100,000 population was a 28 per cent increase over the mean rate for previous years. South Australia (38 cases) reported the majority of cases. All sites reporting cases had an increase in the number of cases notified, except for Queensland where there was a 14 per cent decrease from previous years. There were no cases reported from Tasmania, the Australian Capital Territory or the Northern Territory during 2002.

Figure 15. Notification rates of shiga toxin producing E. coli infections for 2002 compared to mean rates for 1998-2001, by OzFoodNet site



The male to female ratio of cases was 0.3:1 and the highest rates were in 4-9 and 20-24-year-old females (Figure 16). The reason for the strong predominance of females amongst notified cases is unknown. The highest rate was in South Australia, which reported 2.5 notifications per 100,000 population.

Figure 16. Age specific notification rates of shiga toxin producing E. coli infections, Australia, 2002



The majority of cases in South Australia were detected by polymerase chain reaction (PCR) and no typing details were available (Table 4). E. coli O157 was the most common serotype, making up 34 per cent of notifications. This represented an 82 per cent increase in reports of this serotype from the previous year. None of these E. coli O157 isolates were the H7 subtype, although H type was rarely reported. There were six notifications of E. coli O26 making it the second most common serotype. There were no cases of E. coli O111 notified during 2002.

The marked difference in notification rates between states and territories is a result of the practices that pathology laboratories use to screen faecal specimens for toxin producing E. coli. The different tests employed in reference laboratories account for the distribution of E. coli serotypes. Some laboratories predominantly use PCR testing and never culture, which means that a high proportion of notified cases are not definitively identified to the serotype level. South Australia has the most intensive testing regime and test bloody stool (both microscopic and macroscopic) for the presence of the genes coding for production of shiga toxin. Faecal specimens testing positive are then tested using specific PCR assays for virulence characteristics and specific E. coli serotypes. Queensland tests bloody faecal specimens using an enzyme linked immunosorbent assay test kit to detect the presence of shiga toxin. Positive faecal specimens are then tested for STEC using specific PCR tests. Laboratories in most other Australian jurisdictions only test for STEC on request from a doctor or in outbreak settings.

All of the cases appeared to be sporadic, except for one outbreak of E. coli O26 associated with animal contact in South Australia.

Top of pageTable 4. Infecting subtypes of shiga toxin producing E. coli causing diarrhoea, Australia, 2001 to 2002

Organism type	Total 2002	Total 2001
O157	16	8
O26	6	5
O157:H-	3	1
Other E. coli serotype†	3	4
O113	2	1
O157 other H type	1	1
O157:H7	0	1
Untypable	1	2
Not typed‡	23	20
Unspecified	3	6
Total	58	49

† Includes positive reports obtained by PCR that designated specimens as "non-O157 non-O111".
‡ South Australia reported 96% (22/23) of not typed E. coli, which were PCR positive where no culture was obtained or serotyped.

Haemolytic uraemic syndrome

There were 13 cases of haemolytic uraemic syndrome reported during 2002, corresponding to an overall rate of 0.1 case per 100,000 population. New South Wales reported seven of these cases, three of which were notified in the Hunter. Victoria reported four cases, and Queensland and the Northern Territory both reported one case each (Figure 17).

Figure 17. Numbers of notifications of haemolytic uraemic syndrome, Australia, 1998 to 2002, by month of notification and OzFoodNet site



The male to female ratio of cases was 0.7:1 and the highest rate of infection was in females in the 30-34 year age group (0.3 cases per 100,000 population). Sites reported that STEC were isolated for 46 per cent (5/13) of cases (Table 5). Three cases were due to the O157 serotype, making it the most common. There was one case of haemolytic uraemic syndrome due to E. coli O157:H7 during 2002.

Table 5. Notifications of haemolytic uraemic syndrome and infecting subtypes of shiga toxin producing E. coli, Australia, 2001 to 2002

Organism type	Total 2002	Total 2001
O157	1	0
O157:H-	1	0
O157:H7	1	0
O157 other serotype	0	1
Other E. coli serotype	2	0
Untypable	0	2
Unspecified	7	5
No toxigenic E. coli - clinical diagnosis only	1	0
Total	13	8

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