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Bloodborne viruses

The bloodborne viruses notified to NNDSS include hepatitis B, C and D. New HIV diagnoses are notified directly to the National Centre in HIV Epidemiology and Clinical Research (NCHECR), which reports separately in its Annual Surveillance Report. Information on the HIV data collection can be obtained through the NCHECR Website at: http://www.med.unsw.edu.au/nchecr.

Incident hepatitis C virus (HCV) infections are diagnosed by seroconversion (positive for anti-hepatitis C antibodies, with a negative test in the previous year), or by a clinical illness compatible with acute viral hepatitis where other causes have been excluded. Incident hepatitis B virus (HBV) infections are diagnosed by serology (presence of anti-HBc IgM antibodies) or by a clinical illness compatible with acute viral hepatitis where other causes have been excluded. Some jurisdictions may include cases with a previous negative HBsAg test in the last 12 months. Notifications of hepatitis B and hepatitis C that do not meet the incident case definition are recorded as 'unspecified'. Collectively, cases of hepatitis B and C represented 34 per cent of all notifications to the NNDSS in 1999, similar to the proportion in 1998.

Hepatitis B

Incident cases of hepatitis B have been notified to the NNDSS by all jurisdictions since 1994. In 1999, 307 incident cases were reported to the NNDSS at a national notification rate of 1.6 per 100,000 population, consistent with the rate reported in 1998 (1.4 per 100,000 population). The highest rates were recorded in the Northern Territory (9.9 per 100,000 population), Western Australia (2.4 per 100,000 population) and Victoria (2.0 per 100,000 population).

The majority of incident hepatitis B notifications were in the 15-34 year age range (Figure 4). Infections in males exceeded those in females (male to female ratio of 1.8:1). Risk factor information on incident hepatitis B cases were only available from Victoria, where 77 per cent of the cases occurred in injecting drug users (IDU) and their sexual partners. Three incident cases in Victoria were household contacts of a patient with chronic hepatitis B.

Figure 4. Notification rate for incident HBV, Australia, 1999, by age and sex



Unspecified hepatitis B has been notified to the NNDSS by all jurisdictions except the Northern Territory since 1997. In 1999, 8,091 unspecified cases were notified at a rate of 42.7 per 100,000 population (Tables 1 and 2), a rate higher than that recorded in 1998 (35.6 per 100,000 population). The male to female ratio for unspecified cases was 1.2:1. The highest rates of notification were in New South Wales (67.5 per 100,000 population), Victoria (46.1 per 100,000 population) and the Australian Capital Territory (21.4 per 100,000 population). The highest rates were in the 35-39 year age group for men (87.3 per 100,000 population) and the 25-29 year age group for women (77.3 per 100,000 population, Figure 5).

Figure 5. Notification rate for unspecified HBV, Australia, 1999, by age and sex



Vaccination against HBV commenced nationally for 'at-risk' infants in Australia in 1987 (except in the Northern Territory which started in 1988 and South Australia which started in 1996) and in adolescents in 1998 (except New South Wales and South Australia which started in 1999). National universal infant vaccination against HBV started in May 2000. In the Northern Territory, vaccination for Aboriginal infants started in 1988 and universal vaccination in 1990).²⁴ Rates of HBV infection in Australian children are low and it will be some years before the impact of HBV vaccination is seen in older age groups. In the Northern Territory, where infant immunisation with HBV vaccine started 10 years before the rest of the country, there were no child cases of hepatitis B reported in 1999.

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Hepatitis C

It has been estimated that more than 170 million people in the world have been infected with Hepatitis C, five times the number of people infected with HIV worldwide.²⁵ The virus was only identified in 1988, and was one of the first viruses to be identified solely by molecular biology. Serological screening tests became commercially available only in 1990 and while the first generation of assays had problems with both sensitivity and specificity, these have improved in recent years. Nucleic acid-based diagnostic methods are now commercially available. Hepatitis C infection has been notifiable in most Australian jurisdictions since 1991, and the number of 'unspecified' hepatitis C notifications remains stable at around 20,000 notifications per year. Incident cases of hepatitis C have been separately notifiable since 1993. Most cases of hepatitis C are asymptomatic during the acute phase, and incident cases are rarely identified. Most cases are diagnosed when the patient presents with symptoms of chronic disease, or by screening. As the timing of infection is often unknown, most cases are notified as 'unspecified'. The number of notifications to the NNDSS of incident hepatitis C has increased over recent years, although it is recognised that the number of notifications vastly underestimates the true incidence of hepatitis C in Australia. The increase in incident hepatitis C notifications to the NNDSS should not necessarily be interpreted as evidence of increasing transmission in the Australian community. Instead these notifications are largely a product of improved surveillance, increased awareness, and more widespread testing which vary across the jurisdictions.

In 1999, all States and Territories reported unspecified cases of hepatitis C. Incident cases were reported from all jurisdictions except Queensland. The total number of hepatitis C notifications (incident and unspecified) was similar in 1998 and 1999. There were 385 incident cases of hepatitis C reported in 1999, at a rate of 2.5 per 100,000 population. The proportion of all notifications that were known incident cases was 1.8 per cent in 1999, similar to the proportion in 1998 (1.7%). The highest rates of incident hepatitis C infection were reported from the Australian Capital Territory (6.4 per 100,000 population), Western Australia (6.1 per 100,000 population) and South Australia (5.8 per 100,000 population). The majority of incident hepatitis C notifications were in the 15-29 year age range (Figure 6).

Figure 6. Notification rate for incident hepatitis C, Australia, 1999, by age and sex



In 1999 only limited data were collected nationally on incident hepatitis C infections. The Australian Capital Territory, South Australia, Tasmania, Victoria and Western Australia collected additional data on risk factors for infection and the reason for testing or reporting source. The following analyses refer only to incident hepatitis C cases identified in these jurisdictions.

Demographic profile of incident hepatitis C cases

The age and sex of incident hepatitis C cases notified in 1999 are summarised in Table 5, according to the State or Territory of diagnosis. The age of incident cases ranged from 13 to 85 years. The majority of cases were, however, between 20 and 40 years of age. Overall, the male to female ratio of cases was 1.8:1, although the proportion of male cases did vary across jurisdictions, with South Australia recording the highest proportion of male cases.

Table 5. Demographics of incident hepatitis C cases in the Australian Capital Territory, South Australia, Tasmania, Victoria and Western Australia, 1999

	ACT	SA	Tasmania	Victoria	WA
% Males	45	70	56	66	63
Median age (range)
Males	21 (18-30)	25 (17-44)	23 (17-42)	21 (14-40)	27 (18-85)
Females	29 (19-37)	24 (17-74)	31 (17-42)	20 (13-59)	24 (15-50)

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Method of diagnosis of incident hepatitis C

Diagnosis was based either on seroconversion or on the clinical diagnosis of acute hepatitis. In some patients, seroconversion and acute hepatitis were recorded. Data were not available for Victoria, however, data for the other 4 jurisdictions are shown in Table 6. In some jurisdictions the decision of whether a cases in incident or unspecified is made by the clinician. In some of these cases information regarding the method of diagnosis may not be made available to the health department (recorded as unknown in Table 6).

Table 6. Method of diagnosis, incident hepatitis C cases in the Australian Capital Territory, South Australia, Tasmania, and Western Australia, 1999

Method of diagnosis	ACT	SA	Tas	WA
Seroconversion %	75	95	49	58
Clinically defined acute hepatitis %	25	5	-	9
Illness and seroconversion %	-	-	-	2
Unknown %	-	-	51	31

Reporting sources for incident hepatitis C infections

In South Australia the reporting source is recorded, while in the other jurisdictions (the Australian Capital Territory, Tasmania, Victoria and Western Australia), the reason for testing is documented. Recording of multiple responses was possible in Tasmania, while in the remaining jurisdictions recording of one reporting source/reason for test was possible.

A general practitioner was the reporting source for 14 (70%) of the 20 notifications from the Australian Capital Territory, while the remaining 6 cases were identified by screening at a detoxification unit. Prisons were a major reporting source in South Australia, while an investigation of symptomatic hepatitis was the major reason for testing in Tasmania. The reason for testing in Western Australia was often not reported, or reported as 'other'. In Victoria the most commonly identified reason for testing was having another medical problem. The variation across jurisdictions in the recording of the reason for testing or reporting source limits the utility of this information.

Exposure assessment for incident hepatitis C infections

The Australian Capital Territory, Tasmania, Western Australia and Victoria provided exposure assessment data for incident hepatitis C infections. In Tasmania, Western Australia, and Victoria more than one exposure factor was recorded.

Injecting drug use is the major exposure factor for incident infections in all jurisdictions (range 65% in the Australian Capital Territory to 92% in Victoria). Multiple exposures were often recorded, but there were few cases that were not IDU associated. Other risk factors included surgery, tattooing and sexual contact with a hepatitis C-infected person. A proportion of cases had no exposure factor identified, ranging from 1 per cent in Victoria to 24 per cent in Western Australia.

Unspecified hepatitis C accounted for 21,244 notifications; a notification rate of 112 per 100,000 population, similar to the 102.7 per 100,000 population reported in 1998. Of the total notifications of unspecified hepatitis C, 43 per cent of the notifications were from New South Wales. The highest notification rates were from New South Wales (143.7 per 100,000 population), Victoria (130.8 per 100,000 population) and the Northern Territory (120.3 per 100,000 population). The male to female ratio was 1.8:1. The highest notification rates were in the 20 to 49 year age range for both males (318 per 100,000 population) and females (177 per 100,000 population, Figure 7).

Figure 7. Notification rate for unspecified hepatitis C, Australia, 1999, by age and sex

Hepatitis D

Hepatitis D is a co-infection occurring in HBV-infected people and particularly prevalent among injecting drug users.²⁶ There were 21 notifications of hepatitis D to the NNDSS in 1999 at a notification rate of 0.1 per 100,000 population. Of the 21 notifications, 16 (76%) of the notifications came from New South Wales (0.2 per 100,000 population). The majority (85%) of notifications was in males aged between 15 and 49 years.


This article was published in Communicable Diseases Intelligence Volume 25, No 4, November 2001.