Hepatitis C is a blood-borne virus which infects the liver, a high proportion of cases become chronically infected. Exposure is possible through skin breaching activities such as injecting drug use, tattoos, acupuncture, body piercing, medical treatments, occupational exposure, accidents involving blood spills and, occasionally, sexual intercourse. In many cases, infection by the virus has been attributed to the sharing of equipment associated with injecting drug use. Receipt of blood or blood products, prior to the introduction of screening for hepatitis C antibodies in 1990, is also associated with infection.
Newly acquired, asymptomatic cases (incident cases) of hepatitis C virus infection are often difficult to distinguish from newly diagnosed infections of longstanding duration (prevalent cases).
Incident cases of hepatitis C are infections acquired within a defined period of time. They may be identified by recent seroconversion for hepatitis C antibodies or the presence of hepatitis C antibodies accompanied by acute clinical illness not ascribed to other causes. Surveillance data obtained from recently acquired cases provide an insight into current modes of disease transmission, common routes of infection and may identify unusual mechanisms of transmission.
In South Australia, incident cases of hepatitis C infection are commonly identified by changes in serological markers within a defined time frame (Table 1). Hence, negative hepatitis C serology within the previous 12 months, or recent clinical illness accompanied by positive serology where other causes of hepatitis have been excluded, may indicate a newly acquired infection. Positive serology includes detection of antibodies to hepatitis C virus or detection of hepatitis C viral ribonucleic acid (RNA). In the majority of cases, diagnosis of hepatitis C infection is based on a positive antibody test.
Under the 1987 South Australian Health Act, hepatitis C is a controlled, notifiable infection. Since January 1 1995, data have been collected by medical notification of cases. Information collected by medical notification covers patient demographics, markers of clinical illness, possible transmission routes and likely time period of exposure. Data are categorised, cases classified by defined criteria (Table 1) and the information recorded in a database. Validation and checking procedures maintain true and accurate records.
Previous laboratory results are confirmed before final classification of cases. For surveillance purposes, an indeterminate test result is regarded as negative. Some indeterminate results represent recent seroconversion and retesting for antibodies or viral RNA detection is indicated; others may represent false positive results.
Analysis of data is undertaken regularly to identify trends in patterns of infection, ascertain new and current modes of transmission, and to identify cases needing referral for further epidemiological investigation. Data are disseminated in quarterly and annual reports.
Persons considered as possible incident cases are interviewed to determine their testing history, and the timing, location, source and route of exposure to hepatitis C, and to reinforce the need for follow-up. Contact tracing of persons possibly exposed to hepatitis C is carried out where possible.
Table 1. Classification of hepatitis C infection in South Australia.
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Hepatitis C infection (HCV) - case definition |
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Case classifications |
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Incident case (infection of less than 12 months duration) |
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Infection likely to be greater than 12 months |
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Infection of uncertain duration |
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Between 1st January 1997 and 31st December 1998, 124 individuals were identified as incident cases of hepatitis C, acquiring the infection in the preceding 12 months (Summary statistics). Of these, 118 individuals had a previous negative test, five individuals had never been tested before for hepatitis C virus, and the testing history was unknown in one case (Summary statistics).
The group comprised 82 males and 42 females (male to female ratio 1.96:1).
Ten males and nine females were less than 20 years of age at the time of diagnosis. Three individuals were more than 40 years old when infected with hepatitis C virus. The majority of individuals (83%) were aged between 20 and 30 years when diagnosed, and hence at the time of infection (Summary statistics). Nineteen percent of the group were in the 30-39 years age group. By comparison, for prevalent infections over the same period, the age at diagnosis was 20-29 years in 28% of cases and 30-40 years in 41% of cases1.
Although 113 individuals had a history of injecting drug use, it seemed responsible for transmission in only 107 cases (86%). Occupational exposure was a likely source of infection in one case; recent home tattooing appeared responsible for transmission of hepatitis C virus in another. In four cases, recent injecting drug use was strongly denied and no other exposure could be identified; in some of these, earlier test results may have been false negative results (Summary statistics).
Among the 11 cases with no history of injecting drug use, two resulted from household exposure to hepatitis C virus, and one from home-tattooing; in a further case the probable source was occupational exposure to the virus. In two cases no exposure could be identified; one of these had a history of indeterminate tests and was possibly a false positive result (Summary statistics). Overall, three individuals (2%) did not respond to contact letters, these cases were lost to follow-up.
In the majority of cases the racial origin was reported as Caucasian (87%); 10% identified as Aboriginal, one case originated from the Pacific islands and two cases were reported as Asian (Summary statistics).
During 1997 and 1998, 44 (35%) incident cases were diagnosed from tests performed within the prison medical service; 16 (13%) cases were identified from hospital testing and 11 (9%) through drug and alcohol services (DASC). Metropolitan and country general practitioners requested the tests in 47 (38%) instances (Summary statistics).
Compulsory HIV testing at prison entry of persons incarcerated for more than seven days, accompanied by the offer of testing for hepatitis C, ceased during 1998. Despite this change in practice, 30 incident cases were detected in 1998, whereas 14 diagnoses were made from prisons in 1997 (Summary statistics). These numbers reflect serial tests performed on a high-risk population, and do not provide information about the location in which hepatitis C virus was transmitted.
Clinical symptoms of hepatitis were reported in 15 (12%) incident cases.
Summary statistics: incident cases of hepatitis C in South Australia, 1997-8.
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Incident cases of hepatitis C infection |
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Females |
Males |
Total |
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Testing history |
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No previous test |
1 |
4 |
5 |
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Previous negative test, last 12 months |
40 |
78 |
118 |
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Unknown |
1 |
- |
1 |
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Age-group at diagnosis (years) |
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|
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<15 |
1 |
- |
1 |
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15-19 |
8 |
10 |
18 |
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20-29 |
26 |
57 |
83 |
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30-39 |
6 |
13 |
19 |
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40-49 |
1 |
2 |
3 |
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Likely exposure route |
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|
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Injecting drug use |
34 |
73 |
107 |
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Tattoos |
- |
2 |
2 |
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Body piercing |
- |
1 |
1 |
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Occupational exposure |
1 |
1 |
2 |
|
Household |
2 |
- |
2 |
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Unknown |
5 |
5 |
10 |
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Racial origin |
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Aboriginal |
3 |
10 |
13 |
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Asian |
- |
2 |
2 |
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Caucasian |
38 |
70 |
108 |
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Other |
1 |
- |
1 |
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Source of medical notification |
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Hospitals |
8 |
8 |
16 |
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Prisons |
3 |
41 |
44 |
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DASC |
7 |
4 |
11 |
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Mental Health Services |
1 |
1 |
2 |
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Community Health Services |
1 |
3 |
4 |
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General practitioners |
22 |
25 |
47 |
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Total |
42 |
82 |
124 |
Incident cases of hepatitis C infection provide information about current mechanisms of disease transmission. During 1997 and 1998, recent or current injecting drug use was identified as a likely route for hepatitis C virus in 86% of incident cases. Activities in the place of residence (tattooing, body piercing, sharing of bathroom items) were the reported risk exposure in 4% of cases. Hence a small number of types of behaviour were responsible for transmission of hepatitis C in 90% of incident cases detected during the time period. No novel modes of transmission were identified.
Whilst occupational exposure seemed the likely route of infection in two cases, in a further 6% no recent exposure was identified, although some had past behaviour considered to be high-risk for transmission of hepatitis C virus. Overall, 2% of incident cases were lost to follow-up; these cases are unlikely to alter the proportions in identified exposure categories. Few incident cases (12%) reported clinical hepatitis.
The number of incident cases detected in this time period is likely to be an underestimate, partly due to the relatively small proportion of cases demonstrating clinical symptoms. Many incident cases would not have been detected without the offer of standard screening for blood-borne diseases in clinics and institutions dealing with high-risk populations.
Joy Copland
Surveillance
STD Services
September 1999