Hepatitis B virus

Associated infections

• Acute hepatitis B
• Chronic hepatitis B infection
• Cirrhosis
• Hepatocellular carcinoma
• Fulminant hepatic failure (uncommon)
• Reactivation of hepatitis B during immunosuppression or chemotherapy

Transmission route

Transmission occurs through percutaneous or mucosal exposure to infectious blood or body fluids. The dominant global routes are mother-to-child transmission around the time of birth, horizontal transmission in early childhood, sexual contact, sharing of injecting equipment, and unsafe injections or exposure to inadequately reprocessed sharp instruments. Blood carries the highest titre, but the virus is also present in semen, vaginal fluid, wound exudate and saliva, and transmission has been documented through bites and through sharing of items such as razors and toothbrushes that carry small quantities of blood.

In healthcare settings HBV carries the highest per-exposure transmission risk of the three principal bloodborne viruses following percutaneous injury, which is why immunisation of at-risk staff and rigorous sharps management are central controls. Two properties account for this. The first is the very high circulating viral load in some infected people, which can exceed a billion virions per millilitre, so that even a minute residual volume of blood contains an infectious dose. The second is environmental stability: HBV remains infectious on dried surfaces well beyond the survival window of most enveloped viruses, so contaminated equipment surfaces, trolleys and work benches are a plausible intermediate step rather than a theoretical one. Transmission has been documented in the absence of any recalled sharps injury, implicating contact between contaminated surfaces and non-intact skin or mucous membranes.

Patient-to-patient transmission in procedural settings has been documented where injection practices or instrument reprocessing were deficient. The recurring mechanisms are the reuse of syringes or needles between patients, the entry of a used syringe into a multi-dose vial that is then used for other patients, the reuse of single-patient devices such as finger-stick lancing devices and insulin pens, and the reuse of reusable accessories that require sterilisation without an intervening sterilisation cycle. These are failures of practice rather than failures of the disinfection chemistry, and each has been repeatedly identified in published outbreak investigations. Casual contact, food, drinking water and airborne routes play no part in HBV transmission, and there is no evidence of spread through shared washroom facilities or through water used in clinical procedures.

Relevance in endoscopy and reprocessing

HBV is relevant to endoscopy, CSD and dental services because these services generate blood-contaminated reusable instruments and because they administer injectable agents. Correctly performed reprocessing controls the risk effectively. Thorough manual cleaning removes the great majority of organic soil and viral burden from an endoscope, and high-level disinfection with a validated agent inactivates HBV reliably; instruments that penetrate tissue, including biopsy forceps, dental burs and handpieces, and any reusable device entering sterile tissue, require sterilisation rather than high-level disinfection. Where these steps are performed in full and in sequence, the residual risk of HBV transmission through the procedure itself is very low, and published transmission events are attributable to identifiable departures from the process rather than to the process being inherently inadequate.

The breaches that have been identified in bloodborne virus transmission investigations in procedural settings are consistent and specific. They include omission or abbreviation of manual cleaning of the endoscope working channel before disinfection, so that organic soil protects residual virus from the disinfectant; the use of reusable biopsy forceps or other channel accessories that were not sterilised between patients; failure to brush or to replace channel-cleaning brushes and valves; inadequate drying and storage, which permits residual moisture and soil to remain in channels between cases; and unsafe injection practice, most commonly reuse of a syringe on a multi-dose vial that is subsequently accessed for another patient. Automated endoscope reprocessor cycles that are run without a preceding manual clean, or on devices with the wrong connector set, are a further recognised failure. Staff immunisation status and post-exposure protocols form the second layer of control, protecting the workforce where a sharps injury occurs during reprocessing.

Where a breach is identified, the response is structured and time-critical. The implicated device and any associated accessories should be quarantined and removed from service, the reprocessing record and cycle printouts for the affected period retrieved, and the scope of exposure defined by determining every patient processed with the device or vial since the last known compliant cycle. The facility should convene an incident review including infection prevention, the sterilising services manager, the proceduralist and executive, and should notify the state or territory public health unit early rather than after the internal review concludes. Where the review substantiates a breach with credible transmission potential, a look-back is undertaken: affected patients are identified and contacted, offered baseline HBV serology together with HCV and HIV testing, and offered repeat testing at intervals appropriate to the window periods, with counselling and clinical follow-up provided throughout. Because effective post-exposure prophylaxis exists for HBV, prompt identification of recently exposed patients carries direct clinical benefit and is a reason not to delay notification.

Interpreting a detection

HBV is not a rinse-water surveillance target and does not appear in any water quality parameter set applied under AS/NZS 5369. Routine final rinse water monitoring in endoscopy and CSD is directed at organisms that colonise water systems and can recontaminate a reprocessed device at the last wetted step, principally Pseudomonas aeruginosa and other Gram-negative water organisms, non-tuberculous mycobacteria, Legionella species, and total viable count and endotoxin as indicators of system condition. A bloodborne virus that cannot replicate outside hepatocytes has no place in that panel, and no accredited routine water testing method reports it.

When HBV nucleic acid is nonetheless reported on a water or rinse-water sample, the finding should be treated as an artefact until proven otherwise. HBV DNA testing is performed at high sensitivity in laboratories that also process large volumes of clinical serology and molecular samples with very high viral loads, and both specimen carryover and amplicon contamination of reagents, consumables and work surfaces are well-recognised phenomena in that environment. A water sample handled in the same workspace, or extracted on the same run as a high-titre clinical specimen, is a far more probable source of a low-level signal than genuine contamination of a treated water loop. Detection of nucleic acid does not in any case demonstrate the presence of infectious virus.

Resolution should proceed through the laboratory, not through the water system. Confirm sample identity and matrix first, verifying the chain of custody, the sample point identifier, the collection date, the labelling and that the material received was water rather than a clinical specimen. Then establish whether the assay was validated for environmental matrices, since assays are almost invariably validated on serum or plasma and their behaviour on a low-biomass water matrix is undefined; review the extraction blank, the no-template control and the position of the sample in the run relative to any high-titre specimen. Resample from the same point using fresh, unopened consumables and an independent sampling kit, and where possible split the sample between two laboratories. Escalate the result to laboratory quality management for investigation of specimen handling and contamination control. The water safety group should be informed but should not initiate flushing, disinfection, filter changes or system shutdown on the strength of such a result, and the finding should not be recorded as a water quality exceedance. Any genuine concern about HBV transmission at the facility is investigated separately through the exposure and reprocessing-failure pathway described above, which examines reprocessing records, injection practice and patient exposure rather than water quality data.

Antimicrobial resistance

Antiviral resistance is clinically significant in HBV. Long-term nucleos(t)ide analogue therapy suppresses viral replication but rarely eliminates the covalently closed circular DNA template, so treatment is usually prolonged and the virus is under sustained selective pressure. The viral polymerase lacks proofreading capability, generating a broad population of variants from which resistant lineages can be selected whenever suppression is incomplete. Substitutions at rtM204V/I in the reverse transcriptase, often accompanied by the compensatory changes rtL180M and rtL80I, confer resistance to lamivudine and telbivudine and reduce entecavir susceptibility, particularly where these substitutions are joined by additional changes at rtT184, rtS202 or rtM250.

Cumulative lamivudine resistance rates approaching 80% at five years have been reported, which is why current guidance favours agents with a high barrier to resistance, principally tenofovir disoproxil fumarate, tenofovir alafenamide or entecavir in treatment-naive patients. Resistance is typically detected first as virological breakthrough, a confirmed rise in HBV DNA from nadir during continuing therapy, often followed weeks to months later by a rise in transaminases. Adherence should be assessed before resistance is assumed, since non-adherence is a more common cause of breakthrough than genuine resistance. Genotypic resistance testing guides the choice of rescue therapy, and the general principle is to add or switch to an agent without cross-resistance rather than to escalate the dose of the failing drug.

Because the reverse transcriptase and surface antigen reading frames overlap in the compact HBV genome, some resistance mutations simultaneously alter the surface antigen. This raises the prospect of variants with reduced binding to vaccine-induced antibody or to the antibodies used in HBsAg immunoassays, with implications for both vaccine effectiveness and diagnostic sensitivity, and is one reason surveillance of resistance patterns is maintained internationally.

Antiviral resistance affects patient treatment selection and monitoring only. It has no bearing on the susceptibility of HBV to the chemical disinfectants and thermal processes used in instrument reprocessing. Resistance-associated substitutions alter drug binding sites within viral enzymes; they do not confer tolerance of oxidising or alkylating disinfectants, of moist heat, or of the mechanical and detergent action of cleaning. A patient with a multidrug-resistant HBV strain requires no variation to standard reprocessing practice, and no reprocessing parameter should be altered on the basis of a resistance result.