Systematic review of role of polymerase chain reaction in defining infectiousness among people infected with hepatitis C virusBMJ 1997; 315 doi: https://doi.org/10.1136/bmj.315.7104.333 (Published 09 August 1997) Cite this as: BMJ 1997;315:333
- Gregory J Dore, lecturer in epidemiologya,
- John M Kaldor, professor of epidemiologya,
- Geoffrey W McCaughan, clinical associate professorb
- a National Centre in HIV Epidemiology and Clinical Research, University of New South Wales, Darlinghurst 2010, Sydney, Australia
- b The AW Morrow Gastroenterology and Liver Centre, Royal Prince Alfred Hospital, Camperdown 2050, Sydney, Australia
- Correspondence to: Dr Dore
- Accepted 19 May 1997
Objective: To assess the role of polymerase chain reaction in defining infectiousness among people infected with hepatitis C virus.
Design: Published studies of hepatitis C transmission were examined. Twenty nine studies with identified sources of hepatitis C infection who were tested for presence of hepatitis C RNA by polymerase chain reaction were reviewed, including studies of vertical transmission (n=21), transmission after transplantation (n=3), transfusion of blood components (n=3), and needlestick exposure (n=2).
Subjects: All patients identified in studies.
Results: A total of 2022 people who had been exposed to sources positive for antibody to hepatitis C were identified. Among 1148 people exposed to sources positive by polymerase chain reaction 148 cases of transmission occurred compared with no definite case among 874 people exposed to negative sources. Rates of transmission from positive sources were 6.2% for perinatal exposure, 6.1% after needlestick exposure, 78% after solid organ or bone marrow transplantation, and 83% after transfusion of blood components. Other factors influencing risk of vertical transmission were coinfection with HIV and level of hepatitis C viraemia.
Conclusions: Negative results by polymerase chain reaction indicate an extremely low probability of transmission of hepatitis C from a person with antibody to hepatitis C.
Between 20% and 50% of people infected with hepatitis C virus do not progress to chronic infection
Polymerase chain reaction can detect ongoing hepatitis C viraemia and thus the presence of chronic infection
The risk of transmission from people who are positive for hepatitis C antibody but have negative results by polymerase chain reaction is extremely low
The rate of transmission from people who are positive for hepatitis C antibody and have positive results by polymerase chain reaction varies from 6% for mother to child transmission and occupational exposure to about 80% after transplantation or transfusion of blood components
Polymerase chain reaction should be used to define infectiousness among people who are positive for antibodies to hepatitis C
Since the discovery of hepatitis C virus1 and development of a diagnostic assay to detect antibodies against it2 the major pathways of transmission have been reasonably well defined.3 4 Needle sharing among injecting drug users and transfusion of blood products before the introduction of screening for hepatitis C have accounted for most such infections in developed countries. Other modes of parenteral transmission (non-sterile medical and dental equipment, needlestick exposure in the healthcare setting, and tattooing) and mother to child transmission occur, but their population impact has not been reliably estimated.3 Sexual and household contact have been the subject of conflicting reports as to their likelihood of transmission of the virus.5 6 7 8
A key issue that arises in the management of people positive for antibody to hepatitis C is their risk of transmitting the virus by one or more of the above routes. For example, counselling of a pregnant woman positive for hepatitis C antibody would be aided by a clearer understanding of risk factors for vertical transmission. Advice to healthcare workers on their level of risk after needlestick injuries from an infected patient and policy making with regard to healthcare workers positive for the virus would also be helped by an improved understanding of the risk of transmission in these settings.
The development of polymerase chain reaction methods for detecting hepatitis C RNA9 10 has provided a potential means of assessing infected people in terms of their infectiousness. Factors such as level of hepatitis C viraemia and HIV coinfection may also be predictive of risk of transmission. With the goal of estimating the role of such factors in various settings we undertook a review of published studies of hepatitis C transmission.
We sought all published studies which examined transmission of hepatitis C from patients positive for the virus who were tested for evidence of hepatitis C viraemia by polymerase chain reaction for hepatitis C RNA. Studies were identified through searches of Medline and Embase databases to January 1997 and from the bibliographies of published papers. Studies were included if results of polymerase chain reaction for sources of exposure to hepatitis C were recorded. Transmission rates were calculated separately for sources with positive and negative results. Pooled estimates of hepatitis C transmission rates were calculated for different modes of transmission, with transmission rates from individual studies weighted according to sample size. Additional information such as level of hepatitis C viraemia and coinfection with HIV was also sought and the effect of these factors on transmission efficiency examined.
Identification of hepatitis C antibody was generally with enzyme linked immunosorbent assay (ELISA), often with confirmatory recombinant immunoblot assay (RIBA), although first, second, and third generation assays were used in various studies. Detection of hepatitis C RNA was by polymerase chain reaction with primers derived from the 5' non-coding region of the hepatitis C genome. Most studies used “in house” polymerase chain reaction technology with nested primers. Both in house non-nested primers or commercial polymerase chain reaction kits (Roche, Amplicor), or both, however, were used in a few studies. Quantitation of hepatitis C RNA, when performed, used either branched DNA or competitive polymerase chain reaction methods.
A total of 29 articles published between 1992 and 1996 fulfilled the above criteria; 21 of these studies examined vertical hepatitis C transmission 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 with the remainder examining hepatitis C transmission after bone marrow or solid organ transplantation (n=3),32 33 34 transfusion of blood components (n=3),35 36 37 and needlestick exposure (n=2).38 39
Vertical transmission studies
In vertical transmission studies, which included mothers who were positive for hepatitis C by polymerase chain reaction and mothers who were negative (n=18), the percentage of mothers with positive results varied from 33% to 94%, with a pooled estimate of 54% (table 1). Three additional studies selected only those mothers with proved chronic hepatitis C infection.12 17 20 Among 903 children born to mothers positive for hepatitis C by polymerase chain reaction the rate of transmission of hepatitis C varied from 0% to 42%, with a combined rate of 6.2% (95% confidence interval 4.6% to 7.8%). In contrast, no case of transmission was reported among 735 children born to mothers negative by the reaction (0.0% to 0.4%) (table 1). Among positive mothers other factors which were reported to influence transmission were level of viraemia,17 18 20 25 28 coinfection with HIV,19 25 26 and method of delivery.19 The pooled transmission rate for hepatitis C from mothers positive for HIV and hepatitis C antibody was 15.8% (11.8% to 19.8%). In contrast, a transmission rate of 1.9% (1.2% to 2.6%) for hepatitis C was seen among children born to mothers who were seronegative for HIV or of unknown status. In five of seven vertical transmission studies in which measurement of hepatitis C viraemia was performed, transmission was associated with higher level viraemia.17 18 20 25 28 One study demonstrated a significantly higher transmission rate among vaginally delivered infants compared with infants delivered by caesarean section (32% v 6%)19 but showed no association between risk of transmission and breast feeding. Hepatitis C genotype and maternal alanine transferase activity did not correlate with risk of transmission in those studies where these factors were assessed.
Other transmission studies
The three studies examining transmission of hepatitis C from transplant donors positive for hepatitis C antibody to recipients negative for hepatitis C (table 2) gave a pooled transmission rate of 78% (72% to 94%) from donors positive by polymerase chain reaction compared with 0% (0% to 15%) from donors negative by polymerase chain reaction.32 33 34 Three retrospective studies of transmission after transfusion of blood components from donors positive for hepatitis C antibodies demonstrated a pooled transmission rate of 83% (74% to 92%) from donors positive by polymerase chain reaction compared with no definite case of transmission among 97 recipients of blood components from negative donors.35 36 37 One study found two recipients of blood component from donors negative by polymerase chain reaction to be positive for hepatitis C antibody (one negative by polymerase chain reaction, one positive), but pre-existing infection with hepatitis C could not be excluded as they had received multiple previous transfusions. Furthermore, the donor negative by polymerase chain reaction who corresponded to the recipient who was positive for hepatitis C antibody and positive by polymerase chain reaction had two further recipients who underwent testing, both of whom had no evidence of hepatitis C infection.
Although several studies have examined prevalence and incidence of hepatitis C among healthcare workers, only two studies have reported on hepatitis C antibodies and hepatitis C polymerase chain reaction status in source cases of needlestick exposures to healthcare workers (table 3).38 39 With combination of the results of these two studies, the transmission rates for hepatitis C after needlestick exposure to patients positive for hepatitis C antibody was 6.1% (2.3% to 9.9%) from patients positive by polymerase chain reaction and 0% (0.0% to 18.5%) after exposure to those negative by polymerase chain reaction.
The absence of hepatitis C viraemia detectable by polymerase chain reaction seems to indicate an extremely low risk of transmission. In the 29 studies examined, a total of 874 people were exposed to sources positive for hepatitis C antibodies but negative by polymerase chain reaction through vertical, transplant, blood component transfusion, and needlestick exposures. Among these people no definite case of transmission was reported. In contrast, 148 cases of transmission occurred among the 1148 people exposed to sources positive for hepatitis C by polymerase chain reaction. Pooled rates of transmission from such sources were 6.2% after perinatal exposure, 6.1% after needlestick exposure, 78% after transplant exposure, and 83% after transfusion of blood components.
On the basis of vertical transmission studies, level of hepatitis C viraemia and coinfection with HIV are also risk factors for transmission. For mothers positive for antibody to hepatitis C and HIV perinatal transmission occurred in 16% of cases, while the rate of transmission from those seronegative for HIV or of unknown status was less than 2%.
A potential limitation in the estimation of hepatitis C transmission rates is the process of weighting studies according to sample size, with a single large study such as the cohort of women infected with contaminated anti-D immunoglobulin described by Power et al having a large influence on the pooled estimate of vertical transmission. If both retrospective studies of mothers infected with contaminated anti-D immunoglobulin22 23 are excluded, the pooled vertical transmission rate from mothers positive for hepatitis C by polymerase chain reaction increases from 6.2% to 9.7%.
A recent editorial highlighted the importance of individual characteristics associated with an increased likelihood of transmitting hepatitis C in various settings.40 It also asserted, however, that advice to patients with hepatitis C on their infectiousness could not be based on polymerase chain reaction testing for detection of hepatitis C viraemia. The possibility of both false positive and false negative results,41 the difficulty of interpretation of results, and the lack of widespread availability of polymerase chain reaction testing were put forward as supportive arguments. A particular concern was that a person with very low level viraemia could still transmit hepatitis C if the inoculum was large enough.
Advances in technology
Rapid developments in polymerase chain reaction technology, however, have overcome many of these concerns. The sensitivity has been optimised through the use of nested primers based on the very highly conserved 5' non-coding region of the hepatitis C genome.42 Thus, improved standardisation of technology in conjunction with ongoing monitoring by national reference laboratories should limit the possibility of false negative results. The findings from our review also support the high sensitivity of hepatitis C polymerase chain reaction, at least in the setting of research laboratories, where specimens were generally tested in duplicate.
The main drawback of extreme sensitivity of polymerase chain reaction technology is an enhanced possibility of contamination and thus suboptimal specificity. This has been emphasised by an international quality assurance survey which detected false positive results from a large number of laboratories.43 Although increased vigilance to limit contamination and continued monitoring of specificity of the reaction are required, an occasional false positive result does not affect the finding of absent transmission of hepatitis C from patients negative for hepatitis C by polymerase chain reaction and the implications arising from such a finding.
The labour intensiveness of in house polymerase chain reaction technology, in particular nested reaction, has limited its availability. New methods such as nucleic acid amplification systemc (NASBA) and the Amplicor kit (Roche Diagnostic Systems, Basle, Switzerland), however, enable testing of large numbers of specimens in a single day and have equal sensitivity and specificity to the in house methods.44
Our review of published studies of hepatitis C transmission strongly supports the use of polymerase chain reaction testing for determination of infectiousness among people positive for hepatitis C antibodies. Even in situations where the hepatitis C inoculum was large, such as after blood transfusion, no definite case of transmission from a person positive for hepatitis C antibody but negative by polymerase chain reaction was documented.35 36 37
Implications for advice
Despite the improvements in polymerase chain reaction technology we have outlined, we would recommend that a person with hepatitis C is counselled on the basis of a persistently positive or negative hepatitis C polymerase chain reaction (at least two tests over a three month period) rather than a single assessment of polymerase chain reaction status. Even greater consistency would be required in a person receiving or having received interferon treatment because of the fluctuation in hepatitis C polymerase chain reaction status among this group. The greatest benefit would be in identifying those people with antibody to hepatitis C who have no biochemical or clinical evidence of chronic infection and who are persistently negative by polymerase chain reaction. This group of people could be counselled as to their non-infectiousness and most probable lack of chronic hepatitis C infection, with polymerase chain reaction having a similar role to that of hepatitis B virus core antigen in defining infectiousness and hepatitis B virus surface antigen in defining chronic infection.
Pregnant women, or women considering pregnancy, who are positive for hepatitis C antibody could be offered polymerase chain reaction testing to assist in determining their risk of transmitting hepatitis C to their infants; a woman persistently negative by polymerase chain reaction could be reassured that her risk of transmitting hepatitis C perinatally was essentially nil.
Determination of hepatitis C polymerase chain reaction status would also be useful after a needlestick exposure to blood or body fluid from a patient positive for hepatitis C antibody. If the source patient had no biochemical or clinical evidence of chronic hepatitis C infection and was negative by polymerase chain reaction, an exposed healthcare worker could be informed that the risk of acquiring hepatitis C was negligible. This information could allay considerable anxiety over the required 6-9 months before tests for hepatitis C are concluded.
The recent reports of hepatitis C transmission from two cardiothoracic surgeons to their patients has placed increased scrutiny on healthcare workers who are positive for hepatitis C antibody.45 46 In some places surgeons are already prevented from performing procedures likely to risk exposure if they are found to be infected.45 Hepatitis C polymerase chain reaction testing could be used to assess the potential for transmission from infected healthcare workers. While surgeons positive by polymerase chain reaction should be advised not to perform procedures that may lead to exposure, those surgeons who are persistently negative by polymerase chain reaction should not be required to undertake additional infection control measures.
Although transmission efficiency through sexual contact seems to be low, many people positive for hepatitis C antibodies are counselled to use condoms. A person found to be persistently negative by polymerase chain reaction could be advised that the risk of transmitting hepatitis C sexually was essentially nil.
In summary, it seems that there is virtually no risk of hepatitis C transmission in the absence of viraemia as detected by polymerase chain reaction. This finding has important implications with regard to counselling both those people at risk of transmitting hepatitis C and those exposed to infective sources. Additional investigation of transmission based on clinical stage of infection, level of viraemia, and genotype is required to define the level of infectivity further in various settings.
Funding: The National Centre in HIV Epidemiology and Clinical Research is supported by the Australian National Council on AIDS through the Commonwealth AIDS Research Grants Committee.
Conflict of interest: None.