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Gastrointestinal disease

Introduction

Gastrointestinal and foodborne diseases are a major cause of illness in Australia. In 2000, gastrointestinal illness accounted for 21,303 notifications to the NNDSS, which was 23.7 per cent of the total notified diseases. Notifications of foodborne diseases to the NNDSS and notification rates for foodborne diseases in Australia are shown in Tables 11 and 12.

Table 11. Trends in notifications of foodborne disease, Australia, 1991 to 2000*

Disease	1991	1992	1993	1994	1995	1996	1997	1998	1999	2000
Botulism	0	0	0	0	0	0	0	1	0	2
Campylobacteriosis	8,813	9,221	8,070	10,069	11,240	12,109	11,752	13,433	12,657	13,595
Haemolytic uraemic syndrome	-	-	-	-	-	-	-	-	23	15
Hepatitis A	2,234	2,118	1,951	1,912	1,621	2,104	3,044	2,497	1,554	812
Hepatitis E	-	-	-	-	-	-	-	-	9	10
Listeriosis	49	45	49	36	59	70	73	55	64	67
Salmonellosis	5,496	4,416	4,505	5,199	5,873	5,786	7,054	7,613	7,147	6,151
Shigellosis	913	716	691	740	731	680	795	599	547	487
SLTEC,VTEC	-	-	-	-	-	-	-	-	47	33
Typhoid	93	41	80	66	70	80	79	60	68	58
Yersiniosis	329	352	370	311	207	215	207	160	125	73

* All jurisdictions reported for all years with the following exceptions
Botulism not reported from Western Australia.
Campylobacteriosis not reported from New South Wales.
Hepatitis E not reported from Western Australia.
Listeriosis not reported from South Australia (1991) or Northern Territory (1991 to 1993).
Shigellosis not reported from New South Wales.
SLTEC/VTEC not reported from Queensland or Western Australia.
Yersiniosis not reported from New South Wales (1991 to 2000) or Australian Capital Territory (1991 to 1992).

Table 12. Trends in notification rates of foodborne disease, Australia, 1991 to 2000* (rate per 100,000 population)

Disease	1991	1992	1993	1994	1995	1996	1997	1998	1999	2000
Botulism	0.0	0.0	0.0	0.0	0.0	0.0	0.0	< 0.1	0.0	< 0.1
Campylobacteriosis	77.4	80.0	69.2	85.4	94.1	100.1	95.9	108.4	100.8	107.1
Haemolytic uraemic syndrome	-	-	-	-	-	-	-	-	0.1	0.1
Hepatitis A	12.9	12.1	11.0	10.7	9.0	11.5	16.4	13.3	8.2	4.2
Hepatitis E	-	-	-	-	-	-	-	-	0.1	0.1
Listeriosis	0.3	0.3	0.3	0.2	0.3	0.4	0.4	0.3	0.3	0.3
Salmonellosis	31.8	25.2	25.5	29.1	32.5	31.6	38.1	40.7	37.7	32.1
Shigellosis	8.0	6.2	5.9	6.3	6.1	5.6	6.5	4.8	4.4	3.8
SLTEC,VTEC	-	-	-	-	-	-	-	-	0.3	0.2
Typhoid	0.5	0.2	0.5	0.4	0.4	0.4	0.4	0.3	0.4	0.3
Yersiniosis	3.0	3.1	3.2	2.6	1.7	1.8	1.7	1.3	1.0	0.6

* All jurisdictions reported for all years with the following exceptions
Botulism not reported from Western Australia.
Campylobacteriosis not reported from New South Wales.
Hepatitis E not reported from Western Australia.
Listeriosis not reported from South Australia (1991) or Northern Territory (1991 to 1993).
Shigellosis not reported from New South Wales.
SLTEC/VTEC not reported from Queensland or Western Australia.
Yersiniosis not reported from New South Wales (1991 to 2000) or Australian Capital Territory (1991 to 1992).

The true prevalence of gastrointestinal disease is not easy to quantify. There is a significant under-reporting in surveillance data especially of milder gastrointestinal disease. Mead et al¹⁸ have estimated that the notified fraction of foodborne disease in the United States of American (USA) varied from 2 per cent to 50 per cent depending on the severity of the disease. In the UK, it was estimated that for every case of infectious intestinal disease notified there were on average 136 cases in the community.¹⁹ This under-reporting varied depending on the pathogen concerned. In addition there are multiple modes of transmission for the organisms that cause gastrointestinal disease (i.e. some pathogens are also transmitted via other routes). This complicates our ability to estimate what portions of infections are actually transmitted by food. Again, this may vary by disease. The estimated proportion of gastrointestinal disease which is attributable to food ranges from 5 per cent for hepatitis A to 99 per cent for Listeria.¹⁸ Surveillance data may also be biased by different levels of reporting of gastrointestinal disease in different age groups, with children and the elderly more likely to be seen by a medical practitioner.

Differences in laboratory testing practices and surveillance methods in States and Territories may also account for the difference in observed notification rates. This is particularly true for diseases such as Shiga-toxin producing E. coli (STEC/VTEC), where laboratory diagnosis is difficult. States and Territories also have different reporting requirements for doctors and laboratories, which can make national comparison difficult. In 2000, all Australian States and Territories supplied data to the NNDSS on hepatitis A, haemolytic uraemic syndrome, listeriosis, salmonellosis and typhoid. Data on botulism, campylobacteriosis, hepatitis E, shigellosis, Shiga-toxin producing /Verotoxin producing E. coli (SLTEC/VTEC) and yersiniosis were available from most but not all jurisdictions (Table 1). To overcome some of these difficulties, the CDNA agreed to standardise reportable conditions in each jurisdiction from 1 January 2001.

The National Enteric Pathogen Surveillance Scheme (NEPSS) maintained by the Microbiological Diagnostic Unit, Department of Microbiology and Immunology at the University of Melbourne, provide important surveillance data on bacterial enteric pathogens. NEPSS collects, analysis and disseminates data on human enteric bacterial infections diagnosed in Australia. These pathogens include Salmonella,Shigella, E. coli, Vibrio, Yersinia, Plesiomonas, Aeromonas and Campylobacter spp. NEPSS holds more than 140,000 records of human infections and 78,000 records of isolates from non-human sources such as food and animals. NEPSS monitors trends in the epidemiology of human enteric bacterial infections, identifies outbreaks (particularly when geographically and/or temporally dispersed), identifies potential sources of pathogens causing human disease and monitors antibiotic resistance among bacterial enteric pathogens.

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Botulism

There have been no cases of foodborne botulism reported to the NNDSS since the inception of the system in 1991. There were 2 cases of infant botulism reported in 2000, one case each from Victoria and the Northern Territory, both in children aged less than one year.

Infant (or intestinal) botulism cases arise from ingestion of Clostridium botulinum spores, which germinate in the intestine. Spores are widespread and are found in soil and dust as well as in foods such as honey. Symptoms include acute flaccid paralysis (AFP) thus botulism is often identified and reported in the differential diagnosis of AFP, which is an important part of polio surveillance in Australia.

Campylobacteriosis

The rate of campylobacteriosis has steadily increased in Australia since reporting to the NNDSS began in 1991. At 107.1 cases per 100,000 population in 2000, campylobacteriosis is reported more than 3 times as frequently as salmonellosis. Campylobacteriosis is now the most common cause of bacterial gastroenteritis in many industrialised countries.²⁰ The apparent increase in Campylobacter in recent decades reflects the easier laboratory identification due to the development of selective media in the 1980s and polymerase chain reaction (PCR) for Campylobacter in the 1990s. Researchers believe that chicken accounts for between 50 and 70 per cent of Campylobacter infections and it is now recognised that chicken flocks are almost universally infected. Under cooking of chicken or contamination of other foods with juices from uncooked chicken may be the major routes of infection. Consumption of other kinds of foods and contact with animals are also recognised routes. A joint Food and Agriculture Organization of the United Nations (FAO) and WHO expert consultation on risk assessment of microbiological hazards in foods is currently assessing hazard identification and characterisation and exposure to Campylobacter spp. from broiler chickens.²¹Campylobacter infections cause an acute self-limiting gastroenteritis, although a significant proportion of infections may be asymptomatic. C. jejuni infection appears to be an important risk factor in the development of Guillain-Barré syndrome (GBS). The risk of developing GBS is 100-fold higher following a symptomatic episode of C. jejuni infection.²²

There were 13,595 cases of campylobacteriosis notified to the NNDSS with symptom onset in 2000, which was an increase of 7.4 per cent from the 12,657 cases notified in 1999. Reports were received from every jurisdiction except New South Wales where cases are included in the categories 'foodborne disease' or 'gastroenteritis in an institution'. Campylobacter species are the most common cause of gastrointestinal disease notified to the NNDSS. Despite this there are very few outbreaks detected due to the lack of a robust typing method. During 2000, Tasmania reported a small outbreak affecting 3 students in a student residential setting, but no food source was identified.²³ Another cluster of cases in South Australia identified an association between consumption of raw milk and Campylobacter infection.²⁴ Overall, the highest age-specific rate of campylobacteriosis was 281 cases per 100,000 population in 0-4 year-old children (Figure 9). The male to female ratio was 1.2:1.

Figure 9. Notification rates of campylobacteriosis, Australia, 2000, by age and sex



The highest notification rate was in South Australia (125.7 cases per 100,000 population) and the lowest rate was in the Northern Territory (93.1 cases per 100,000 population). Reports of campylobacteriosis were more frequent in Spring and Summer (Figure 10).

Figure 10. Trends in notifications of campylobacteriosis, Australia, 1991 to 2000, by month of onset



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Hepatitis A

Overall hepatitis A in Australia has declined significantly over the past 30 years although levels in Indigenous communities have remained high. National notifications of hepatitis A have declined considerably since the peak rate recorded in the NNDSS in 1997 (16.4 cases per 100,000 population). The impact of control measures, including vaccination of susceptible populations and improvements in hygiene, have clearly had an impact on the incidence of hepatitis A in Australia (Tables 11 and 12).

In Australia, three patterns of hepatitis A epidemiology are recognised.²⁵ Firstly, there are large, slowly evolving community outbreaks, occurring at intervals of 5 years. Community outbreaks affect groups of people prone to infection, who are susceptible to intense levels of transmission within their groups. Infected individuals are also a potential source for infection for the wider community. Settings for community outbreaks include child care centres and pre-schools, communities of men who have sex with men, schools and residential facilities for the intellectually disabled and communities of injecting drug users. Secondly, sporadic cases of hepatitis A may arise in people without obvious risk factors although some may be associated with overseas travel or travel to Indigenous communities. Thirdly, point-source outbreaks of hepatitis A may arise from contaminated food or water or an infected food-handler. These are relatively rare in Australia. The last major point-source outbreak of hepatitis A arose from contaminated oysters in New South Wales in 1997.²⁶

Vaccination against hepatitis A in Australia is recommended for travellers to endemic areas, visitors to remote Indigenous communities, childcare and pre-school personnel, the intellectually disabled and their carers, healthcare workers, sewerage workers, men who have sex with men, injecting drug users, patients with chronic liver disease (or with hepatitis C), haemophiliacs who may have received pooled plasma concentrates, and food handlers.²⁵

There were 812 cases of hepatitis A notified to the NNDSS with symptom onset in 2000, which was a decrease of 48 per cent from the 1,554 cases notified in 1999 (Figure 11). The highest age-specific rate was in the 25-29 year age group (8.4 cases per 100,000 population) (Figure 12) and the male to female ratio was 1.5:1.

Figure 11. Trends in notification rates of hepatitis A, Australia, 1994 to 2000, by year of onset



Figure 12. Notification rates of hepatitis A, Australia, 2000, by age and sex



The highest notification rate was in the Northern Territory (22.5 cases per 100,000 population) and the lowest rate was in Tasmania (0.6 cases per 100,000 population). There has been a marked decline in notifications of hepatitis A throughout north Queensland since hepatitis A vaccination was introduced for Indigenous children in the region in early 1999 (J. Hanna, personal communication).

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Hepatitis E

Hepatitis E is endemic in many countries of Asia but is rarely reported in Australia. Women in the third trimester of pregnancy are susceptible to fulminant hepatitis E disease, with a case fatality rate as high as 20 per cent.²⁷ Outbreaks in South Asia pose a risk to Australian travellers to these regions. There were 10 cases of hepatitis E notified to the NNDSS in 2000, 9 from New South Wales and one from Tasmania. Of the 10 cases, one was associated with travel to India. There was no travel history available for the remaining cases.

Listeriosis

Listeriosis is a serious but relatively rare foodborne disease to which neonates, pregnant women, the immuno-compromised and the elderly are particularly susceptible. In pregnant women the infection can be passed to the foetus. Infants may be stillborn, born with septicaemia or develop meningitis in the neonatal period. Clusters of cases of listeriosis have been noted in hospitals, nurseries and aged care facilities.²⁷

The notification rate of listeriosis in Australia has remained steady over the past 10 years (Tables 11 and 12). As food preparation practices change a variety of products have been found to be vehicles for Listeria spp. The Australian Quarantine Inspection Service (AQIS) and the Australia New Zealand Food Authority are responsible for the laboratory testing of food imported into Australia. Between 1995 and 1998, Listeria contamination of foods such as smoked fish and soft cheeses, constituted the most frequent findings.²⁸

Listeriosis was notifiable in all Australian jurisdictions in 2000; however practices varied as to whether a materno-foetal case constituted one or two cases. There were 67 cases of listeriosis reported to the NNDSS in 2000, which was a similar number to previous years (Table 11). The highest age-specific rate of listeriosis was 2.0 cases per 100,000 population in the 80-84 year age group (Figure 13) and the male to female ratio was 0.7:1.

Figure 13. Notification rates of listeriosis, Australia, 2000, by age and sex



The highest notification rate was in the Northern Territory (1.5 cases per 100,000 population) There were no cases reported from the Australian Capital Territory. There was no clustering of cases of listeriosis. Five materno-foetal pairs were reported which resulted in three foetal deaths.

Salmonellosis (excluding typhoid)

Salmonellosis remains the second most common cause of gastroenteritis in Australia and the most important cause of bacterial foodborne disease outbreaks. In 2000, rates of Salmonella notifications fell for the second year running, to 32.1 cases per 100,000 population.

There were 6,151 cases of salmonellosis reported to the NNDSS with symptom onset in 2000, which was a decrease of 13.9 per cent from the 7,147 cases reported in 1999 (Table 11). The highest age-specific rate was 179.2 cases per 100,000 population in 0-4 year-old children (Figure 14) and the male to female ratio was 1:1. The highest notification rate was in the Northern Territory (155.5 cases per 100,000 population) and the lowest rate was reported from Victoria (21.4 cases per 100,000 population).

Figure 14. Notification rates of salmonellosis, Australia, 2000, by age and sex



The Kimberley Statistical Division in Western Australia had the highest rate of salmonellosis, in excess of 399 cases per 100,000 population, which was comparable to previous years (Map 2). Reports of salmonellosis were greatest in the months of January to March (Figure 15).

Top of pageMap 2. Notification rates of salmonellosis, Australia, 2000, by Statistical Division of residence



Figure 15. Trends in notifications of salmonellosis, Australia, 1991 to 2000, by month of onset



The NEPSS reported 6,121 cases of Salmonella in 2000.²⁹ The top 10 Salmonella infections reported to NEPSS are shown in Table 13.

Table 13. Top 10 isolates of Salmonella, Australia, 2000 (data from the National Enteric Pathogen Surveillance Scheme)*

Isolate	ACT	NSW	NT	Qld	SA	Tas	Vic	WA	Aust	% of total
S. Typhimurium PT 135†	10	148	2	143	6	6	69	221	605	9.9
S. Typhimurium PT 9†	32	187	3	57	24	22	178	47	550	9.0
S. Virchow†	8	56	4	256	16	2	110	6	458	7.5
S. Saintpaul†	6	39	20	186	26	2	15	47	341	5.6
S. Enteriditis	5	55	5	72	14	9	32	56	248	4.0
S. Typhimurium PT 64	1	101	1	19	16	1	77	10	226	3.7
S. Birkenhead†	1	77	0	100	4	1	13	0	196	3.2
S. Muenchen†	2	21	10	40	11	0	7	29	120	2.0
S. Chester	0	13	17	38	18	0	5	17	108	1.8
S. Bovismorbificans	0	45	2	13	7	1	27	10	105	1.7
Others	0	0	0	0	0	0	0	0	3,164	51.6
Total	65	742	64	924	142	44	533	443	2,957	48.3

* Adapted from NEPSS annual report, 2000
† Associated with an identified outbreak

NEPSS recorded 19 outbreaks of Salmonella in Australia in 2000. One outbreak, which was S. Paratyphi B bv Java RDNC/AUS2 associated with fish tanks, was Australia-wide while all others were confined to a single jurisdiction. Six outbreaks were recorded in South Australia, three each in New South Wales and Western Australia, two each in Queensland and Victoria and one each in the Australian Capital Territory and the Northern Territory. No Salmonella outbreaks were reported from Tasmania. The largest outbreak was of Salmonella Typhimurium PT135 in Western Australia. This outbreak continued through the year with peaks of reports in February, April and May. All age groups were affected but no food vehicle or common source was identified.

South Australia reported an outbreak of Salmonella Typhimurium PT44 in October 2000.³⁰ Ten cases were associated with eating at an Adelaide restaurant and although an investigation found lapses in hygienic practices, no food source for this outbreak was identified.

An outbreak of Salmonella Mgulaniinvolving 42 laboratory-confirmed cases in December 1999 to January 2000 occurred in New South Wales.³¹ No environmental or food source was identified and DNA 'fingerprinting' suggested the strains had been circulating in Australia for some years.

Salmonella Enteriditis was the most common salmonella infection among travellers returning from overseas in 2000. Of 142 cases, there were 85 cases of S. Enteriditis phage type 4.

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Shigellosis

In 2000, the NNDSS notification rate of shigellosis fell for the third year running, and was the lowest rate recorded since the surveillance system began. There were 487 cases of shigellosis reported to the NNDSS with onset of symptoms in 2000, which was an 11 per cent decrease from 547 cases reported in 1999. The highest age-specific rate was 18 cases per 100,000 population in 0-4 year-old children (Figure 16) and the male to female ratio was 1.2:1.

Figure 16. Notification rates of shigellosis, Australia, 2000, by age and sex



Reports were received from every jurisdiction except New South Wales where cases are included in the categories 'foodborne disease' or 'gastroenteritis in an institution'. The highest notification rate was in the Northern Territory (58.3 cases per 100,000 population) and the lowest rate was reported from Tasmania (0.4 cases per 100,000 population). Cases were more commonly notified during the months of January to April (Figure 17).

Figure 17. Trends in notifications of shigellosis, Australia, 1991 to 2000, by month of onset



Reports of Shigella to the NEPSS identified 147 cases of S. sonnei biotype g among gay men in inner city Sydney. This outbreak was associated with casual sex at sex-on-premises-venues.³² (O'Sullivan et al Communicable Diseases Control Conference 2001, Abstract No.31).

Shiga-like toxin producing Escherichia coli/Verotoxin-producing E. coli

There were 33 cases of STEC/VTEC reported to the NNDSS with symptom onset in 2000, which was a 24 per cent decrease from 43 cases reported in 1999. SLTEC/VTEC was a notifiable disease in 2000 in all jurisdictions except Queensland and Western Australia. In 2000, all of the 33 cases of SLTEC/VTEC were reported from South Australia. This reflects the practice in South Australia of screening faecal specimens from all cases of bloody diarrhoea for toxin genes, by PCR.

The highest age-specific rate was 0.9 cases per 100,000 population in the 80-84 year age group and the male to female ratio was 1.8:1.

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Haemolytic uraemic syndrome

Infections with SLTEC/VTEC have the potential to cause severe and life-threatening illness including haemolytic uraemic syndrome (HUS). Haemolytic uraemic syndrome will generally be diagnosed on the basis of microangiopathic haemolytic anaemia, acute renal impairment and thrombocytopaenia (reduced platelet counts). Children aged less than 5 years are at increased risk of haemolytic uraemic syndrome. In an outbreak of HUS associated with the consumption of mettwurst in South Australia in 1994/1995 there was one death and 18 children required dialysis.³³

There were 15 cases of HUS notified to the NNDSS with symptom onset in 2000 (Table 11). There was no evidence of clustering among HUS cases.

The highest age-specific rate was 0.6 cases per 100,000 population in 0-4 year-old children and the male to female ratio was 1.1:1.

Typhoid

Typhoid notifications in Australia are strongly associated with overseas travel. Since the majority of cases are imported, the education of overseas travellers, especially young people travelling in Asia, is the most important public health action to control typhoid in Australia.

There were 58 cases of typhoid reported to the NNDSS with symptom onset in 2000, a reduction of nearly 15 per cent compared with the 68 cases reported in 1999. Of the 56 isolations of S. Typhi by NEPSS in 2000, all but 2 cases had a history of travel (mostly in Asia) prior to onset.

The highest age-specific rate was 0.7 cases per 100,000 population in the 20-29 year age group (Figure 18) and the male to female ratio was 1.5:1. The highest notification rate was in Western Australia (0.6 cases per 100,000 population).

Figure 18. Notification rates of typhoid, Australia, 2000, by age and sex



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Yersiniosis

The notification rate for yersiniosis has fallen over the 10-year period from 1991 to 2000. These declines are a worldwide phenomenon and may relate to changes in laboratory testing of faeces and improvements in animal slaughtering practice (M. Barton, personal communication, January 2002). The steady decline in the incidence of this disease and a lack of outbreaks lead the CDNA to remove yersiniosis from the national notifiable diseases list in January 2001.

Yersinia enterocolitica, the causative organism of yersiniosis, causes both sporadic cases and disease outbreaks, with pork a frequently incriminated food.²⁷ Person-to-person transmission has been documented in outbreak settings and direct transmission from dogs to humans has been postulated.

There were 73 cases of yersiniosis reported to the NNDSS with dates of symptom onset in 2000, which was a 42 per cent decrease from the 125 cases reported in 1999. The highest age-specific rate was 2.6 cases per 100,000 population in 0-4 year old children (Figure 19) and the male to female ratio was 1.5:1. Reports were received from every jurisdiction except New South Wales where cases are included in the categories 'foodborne disease' or 'gastroenteritis in an institution'. The highest notification rates were in Queensland (1.7 cases per 100,000 population) and the Northern Territory (1.0 cases per 100,000 population).

Figure 19. Notification rates of yersiniosis, Australia, 2000, by age and sex

Policy initiatives in foodborne disease surveillance and control in 2000

A Food Policy Unit was formed within the Commonwealth Department of Health and Ageing in 2000. The Unit aims to coordinate policy development with a focus on food safety; strengthening the evidence base for decision making; fostering collaboration between government, consumers and the food industry; and promoting nationally consistent policy regulation and action.³⁴

In the latter part of 2000, the Commonwealth Department of Health and Ageing established and funded a collaborative network called 'OzFoodNet' to enhance surveillance mechanisms for foodborne disease across Australia. The aims of OzFoodNet are to:

• estimate the incidence of foodborne disease in Australia;
• learn more about the causes and determinants of foodborne disease;
• identify risky practices associated with food preparation and handling;
• train foodborne disease epidemiologists.

The work of OzFoodNet will improve surveillance of foodborne disease across Australia. Collaborators of OzFoodNet include State and Territory health authorities, the National Centre for Epidemiology and Population Health, the Public Health Laboratory Network and national government agencies.³⁵


This article was published in Communicable Diseases Intelligence Volume 26, No 2, June 2002