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Surveillance of newly acquired hepatitis C infection (incident cases) in South Australia, 1995 to 2000.

Our feature article this quarter describes a subset of those infected with hepatitis C virus. Data collected by medical notification is supplemented by information obtained during interview with an epidemiologist. These data describe the group infected and common behaviours associated with recent transmission of hepatitis C virus.

Introduction

Hepatitis C virus (HCV) is a blood-borne virus that infects the liver and is a major health problem worldwide.¹ Few acute hepatitis C infections demonstrate clinical illness, and a high proportion of cases progress to chronic infection.¹ Exposure to HCV is possible through skin breaching activities such as injecting drug use (IDU), tattooing and other means of skin piercing. In many infections, exposure to the virus is attributed to the sharing of equipment associated with IDU. Receipt of blood or blood products, before the introduction of screening for hepatitis C antibody in 1990, is also associated with HCV infection. Occasionally, HCV may be transmitted through sexual intercourse.

Notification of HCV in South Australia

Since 1st January 1995, hepatitis C infection has been designated a controlled, notifiable disease under the Public and Environmental Health Act, making laboratory and medical reporting of cases a legal requirement.

More than ten thousand cases of hepatitis C infection have been diagnosed in South Australia since HCV antibody tests became available in 1990. Each year, approximately one thousand people are diagnosed with hepatitis C infection in South Australia.² Fewer than ten percent of diagnoses of HCV infection are identified as newly acquired infection (incident cases); the majority are infections of longstanding duration (prevalent cases).

Incident cases of HCV - newly acquired infections

Incident infections of HCV in South Australia are identified by seroconversion for hepatitis C antibodies in the preceding 12 months or the presence of hepatitis C antibodies accompanied by acute clinical hepatitis not ascribed to other causes.

Monitoring incident cases of HCV infection provides insight into current modes of disease transmission, common routes of infection and may identify unusual mechanisms of exposure. This information directs public health activities to interrupt the chain of transmission.

Incident cases of hepatitis C infection in South Australia are identified by changes in serological markers of infection. Positive serology includes detection of antibodies to HCV or detection of hepatitis C viral ribonucleic acid (RNA). In the majority of cases, the diagnosis of hepatitis C infection is based on a positive antibody test.

Potential incident cases of HCV infection are interviewed to determine their testing history and the timing, location, source and probable routes of exposure to HCV.

Figure 1. Newly acquired infections (Incident cases) of hepatitis C in
South Australia, 1995 - 2000. Year of diagnosis by sex.

Case Descriptions

Between 1 January 1995 and 31 December 2000, 364 incident cases of HCV infection were notified in South Australia, 228 males and 136 females (Figure 1). The incident case group had a male to female ratio of 2.1:1, compared to a male to female ratio of 1.8:1 for all diagnoses of HCV in the same period.^2,3

Of the 364 cases, 347 had had a previous negative test, of which 336 were in the previous 12 months; 11 cases with clinical hepatitis had a negative test more than 12 months before their HCV diagnosis. Fourteen cases had never been tested before for HCV but had clinical hepatitis; the testing history was unknown in three cases with a clinical illness.

Clinical symptoms of hepatitis were reported in 46 (13%) of the 364cases, 25 males and 21 females.

Most cases (84%) were reported as Caucasian, and 13% identified as Aboriginal. Few cases were diagnosed in people of Asian origin (Table 1).

Age data

Among those aged less than 20 years at diagnosis, the male to female ratio was 1:1.3, in contrast to older age groups where males were in the majority (Figure 2). Although the age range at the time of diagnosis of HCV infection was 14 to 74 years, the majority of cases (77%) were less than 30 years of age.

Sixteen people (4%) were more than 40 years old when diagnosed with HCV infection and 19% were in the 30 - 39 year age group. Among prevalent HCV infections diagnosed in the same period, the age group at diagnosis was 20 - 29 years in 28% of cases, 30 - 39 years in 37% of cases and 40 - 49 in 21% of cases.^{2 3}

Figure 2. Newly acquired infections (Incident cases) of hepatitis C in
South Australia, 1995 - 2000. Age-group at diagnosis by sex.

Cases reporting injecting drug use

Among 364 cases of newly acquired HCV infection, 335 (92%) were reported as having a history of IDU. In 309 cases, IDU alone was reported as the likely route of transmission of HCV; recent or current IDU was confirmed in 271 of these cases, and no details are available for the other 27 cases. One male among the 271 cases with recent IDU also had a male sexual partner with HCV. In 20 further cases, the person was reported as having a history of IDU and tattoos, however the timing of the respective exposures (IDU, tattoos) is unknown (Table 1).

Six incident cases claimed past, but not recent, IDU. Current or recent IDU was strongly denied in four cases, and no alternative exposure could be identified; in some, the earlier negative test result may have been a false negative report. Recent injecting drug use was also denied in two institutionalised cases; occupational exposure was claimed in one case and recent tattooing was the likely source of exposure in the other.

Cases with no history of injecting drug use

Among 29 cases with no history of IDU, two reported sharing razors with household members with HCV infection. Male-to-male sexual transmission appeared to be the mode of transmission in one case with a long-term sexual partner with hepatitis C infection; in one other case, with no further details, the sexual partner was nominated as the source of infection.

Although exposure through an occupational source of infection was likely in one case, no incident likely to result in transmission was recalled; no details are available for another case reported to be from occupational exposure to HCV.

Recent tattooing at home appeared responsible for transmission of HCV in one case and body piercing in another. In two further cases tattooing was reported as the exposure to HCV. The likely source of exposure to HCV in another case was sharing of a medical home-use finger-prick device.

In eleven cases where no exposure could be identified, six had a history of indeterminate test results and were possibly false positive results. One further case was likely to have been exposed occupationally many years earlier, and the earlier negative test result may have been an error.

Seven cases (2%) were lost to follow-up. Information provided at notification in these cases was incomplete and the source of exposure to HCV remains unknown.

Table 1. Summary statistics: Incident cases of hepatitis C infection in South Australia, 1995-2000.

Summary

Surveillance of incident HCV infection indicates current transmission of HCV in South Australia is primarily through injecting drug use. The number of incident cases of HCV infection diagnosed in this time period is likely to be an underestimate, partly due to the relatively small proportion of cases demonstrating clinical symptoms. Many cases would not have been detected without institutional screening for blood-borne infections in high-risk populations.

Activities in the place of residence (tattooing, body piercing, sexual activity, sharing of bathroom items and home-use medical device) were the reported risk exposure in many non-IDU cases.

In two cases, unusual modes of transmission were identified. Male-to-male sexual transmission was likely in one case; a male with a long-term male partner diagnosed with hepatitis C infection seven years earlier. In the other, sharing of a home use finger-prick device by a couple in a long-standing partnership seemed responsible for transmission of HCV. Attempts to genotype the virus in the index and likely source were unsuccessful, as the index case was RNA negative at three months.

While occupational exposure seemed the likely route of infection in one case, specific exposure to blood could not be remembered. Among the cases in which no recent exposure was identified at interview, some had past behaviour considered to be high risk for transmission of HCV. Two cases in this group were inmates of institutions and the circumstances of the interview may have resulted in incomplete disclosure of behaviours at high risk for exposure to HCV.

Overall, seven incident cases were lost to follow-up. When combined with those cases for which no exposure was identified at interview, the transmission route of HCV remains unknown in six percent of incident cases for the period.

Ongoing monitoring of the hepatitis C status of people at risk will assist in future identification of cases of newly acquired hepatitis C infection. Prevention efforts focussed on safer injecting drug use may have the greatest potential for decreasing current transmission of HCV in South Australia.

References:

1. Alter MJ, Kruszon-Moran D, Nainan OV et al. The prevalence of hepatitis C virus infection in the United States, 1988 through 1994. N Engl J Med 1999; 341 (8): 556-562.
2. STD Control Branch. Sexually Transmitted Diseases in South Australia, Epidemiologic Reports 9 - 12, 1995, 1996, 1997, 1998. Public and Environmental Health Service, Department of Human Services. ISSN 1033-0607. www.stdservices.on.net/publications
3. STD Services. Sexually Transmitted Diseases in South Australia, Epidemiologic Reports 13 & 14, 1999, 2000. Internal Medicine Service, Royal Adelaide Hospital. ISSN 1033-0607.
4. STD Control Branch. Quarterly Surveillance Reports, 1996-1999. Public and Environmental Health Service, DHS. ISSN 1328-0090. www.stdservices.on.net/publications
5. STD Services. Quarterly Surveillance Reports, 1999-2000. Internal Medicine Service, Royal Adelaide Hospital. ISSN 1328-0090. www.stdservices.on.net/publications

Joy Copland,

March 2001.

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