Bloodborne diseases

Bloodborne diseases which are reported by State and Territory Health Services to the National Notifiable Diseases Surveillance System (NNDSS) include hepatitis C, hepatitis B and hepatitis D. All newly diagnosed cases of HIV are reported to the National Centre in HIV Epidemiology and Clinical Research (NCHECR) and reports of these for 1997 have been published separately in the 1998 surveillance report from NCHECR.11 The NCHECR website is: http://www.med.unsw.edu.au/nchecr/

National case definitions for incident hepatitis B and hepatitis C require the presence of current illness together with serological evidence of infection or alternatively, specific serological evidence of recent infection or seroconversion.¹ Notifications for hepatitis B or hepatitis C which are not accompanied by evidence of recent infection are classified as 'unspecified'.

In 1997, the bloodborne hepatitides accounted for 30 per cent of all notifiable diseases. Hepatitis C, both incident and unspecified, accounted for more notifications than any other notifiable disease. The bloodborne hepatitides, in particular hepatitis C, have had the highest age specific notification rates in the 20 to 40 year age groups, making them a major public health concern in young adults.

Hepatitis C

For 1997 all states, excepting New South Wales and South Australia, reported unspecified cases of hepatitis C to the NNDSS on a monthly basis. Data from both South Australia and New South Wales have been retrospectively collated and incorporated into the current report (Map 2).

For 1997, 81 cases of incident hepatitis C were reported, and rates of infection were 0.5 per 100,000. Unspecified hepatitis C accounted for 19,692 notifications, of which 45 per cent were reported from New South Wales. National rates of hepatitis C (unspecified) were 106 per 100,000. Sixty-six per cent of all hepatitis C notifications were in the 20 to 44 year age group (Figure 1).

In 18,610 notifications the sex was reported. Of these 11,858 (64%) were male and 6,752 (36%) female.

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Map 2. Notification rate of hepatitis C (unspecified), 1997, by Statistical Division of residence

Figure 1. Notification rate of hepatitis C (unspecified), 1997, by age group and sex

Hepatitis B

Since 1994, all States and Territories have distinguished incident hepatitis B in data provided to the NNDSS.

There were 247 cases of hepatitis B (incident) reported in 1997. This corresponds to a notification rate of 1.3 per 100,000 which is consistent with the rate of 1.2 per 100,000 reported in 1996. The highest rates of incident hepatitis B were reported from the Northern Territory (10.2 per 100,000) and Victoria (2.6 per 100,000). The male to female ratio for hepatitis B notifications is 1.6:1.

Age specific notification rates were highest in the 20 to 24 year age group at 4 per 100,000. Rates of incident hepatitis B increased markedly over the age of 14 years and declined over the age of 40. In 1997 there were 9 notifications of hepatitis B in children under the age of 15 years. Two notifications were reported in children in the 0 to 4 year age group (Figure 2).

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Figure 2. Notification rate of incident hepatitis B, 1997, by age group and sex

Hepatitis D

There were 13 cases of hepatitis D in 1997. The male to female ratio was 5.5:1. All reports were in adults aged between 20 and 50 years of age.

Discussion

Although primarily bloodborne, hepatitis C can be vertically transmitted while sexual transmission occurs rarely, if at all. The spectrum of illness caused by hepatitis C includes acute infection, chronic asymptomatic infection, chronic disease, cirrhosis and hepatocellular carcinoma. Acute hepatitis C often goes unrecognised, as the symptoms can be mild. In the absence of symptoms, the diagnosis can only be confirmed by documentation of prior testing and seroconversion. Incident hepatitis C is not separated from unspecified notifications of the disease in Queensland. As such it is under reported in the National data set.

Of those exposed to hepatitis C, 70 per cent can be expected to develop chronic infection, and 20 to 30 per cent of these will develop cirrhosis. The clinical severity of acute illness does not relate to progression to chronic disease. Outcomes of hepatitis C exposure relate to many factors including HCV subtype, virus titre in the infective source, age at infection, duration of disease, mode of acquisition, coinfection with hepatitis B, or HIV, host immunity and alcoholism.¹² Hepatitis A superinfection can also predispose to fulminant hepatitis, and therefore a worse prognosis in those with pre-existing hepatitis C.¹³

The highest risk group for transmission of HCV in Australia is injecting drug users (IDUs). Rates of seroconversion in IDUs have been reported between 15 and 40 per 100 person years.¹⁴ Tattooing and the health care setting are other potential sources of bloodborne transmission. Prior to 1990 transfusion related hepatitis C figured as a significant risk factor in transmission. Since 1990, the screening of blood products for hepatitis C has been routine. The relative contributions of risk factors in the transmission of hepatitis C in Australia is not able to be ascertained from NNDSS data.

The potential for hepatitis B to be sexually and vertically transmitted is greater than is reported to occur with hepatitis C.¹² Higher rates of hepatitis B occur in Indigenous Australians, migrants from Asian countries, IDUs, homosexual males and household contacts of known hepatitis B cases.¹⁵ Vertical transmission is increased if the mother is known to be HBeAg positive. The risk of becoming a hepatitis B carrier is almost two-fold higher if the disease is acquired between the ages of 0 to 4 years as compared to 5 to 12 years.¹⁵ This underscores the importance of screening and vaccination of high risk infants born to mothers in the above mentioned risk categories.

Hepatitis D can only occur in a person with pre-existing hepatitis B. It must be assumed therefore that all cases of hepatitis D occurred as an acute coinfection with hepatitis B, or as a superinfection in a person with chronic hepatitis B infection. Hepatitis B is an obligate risk factor for this disease, and hepatitis D control is inextricably linked to public health efforts to control hepatitis B.

This article {extract} was published in Communicable Diseases Intelligence Vol 23 Number , 21 January 1999 and may be downloaded as a full version PDF from the Table of contents page. Volume 23 1999.