November 12, 2014

expert reaction to recall of 22,000 dental patients following dentist malpractice

Thousands of dental patients of a Nottinghamshire dentist have been called for tests following concerns over infection control, although the risk of infection is thought to be low.

Prof David Evans, Professor of Virology, University of Warwick, said:

“There are two possible sources of blood-borne viruses that could be acquired during a visit to the dentist. The first is from the dental practitioner, when a minor cut through a protective glove could lead to direct exposure of the patient’s blood with that of the dentist (although reports from NHS England suggest that this dentist was not infected with any blood-borne viruses). The second is through exposure of the patient’s blood to gloves or instruments that have been contaminated with blood from a previous patient

“The three most significant blood-borne virus infections are HIV, HCV (hepatitis C virus) and HBV (hepatitis B virus). Adherence to normal protective measures such as hand washing, changing gloves between patients, and using sterile instruments is usually sufficient to prevent patient to patient transmission of any of these three viruses within a dental surgery. That is why these protective measures are used. Reports from NHS England suggest that the dentist was not infected with these viruses.

“Although globally very large numbers of people are infected with HCV and HBV, the incidence in the UK of individuals carrying these viruses (which may cause lifelong infection) is low. HBV prevalence is thought to be below 0.5% and HCV prevalence between 0.5 and 1%, although the prevalence varies between communities. Potential exposure therefore depends upon the dental procedures involved and the likelihood of gloves or instruments being contaminated from a previous patient. Many individuals exposed to HBV and HCV as adults will naturally clear the infection. A proportion will become chronically infected and may develop liver disease. Testing for infection is likely to involve screening for viral protein or nucleic acid in the blood. There is an excellent vaccine to prevent HBV infection which many who have travelled abroad will have been immunised with. There is no vaccine for HCV but newly developed and licensed anti-viral drugs against this virus are effective.”

Prof Will Irving, Professor and Honorary Consultant in Virology, University of Nottingham and Nottingham University Hospitals NHS Trust, said:

“The concern here is a breakdown of infection control procedures that may have resulted in onward transmission of blood-borne viruses. Outbreaks of hepatitis B and C virus infection arising from failure to comply with strict infection control procedures are well documented in the literature. There is thus a risk that patients attending this dental surgery may have acquired infection through this route.

“It is hard to quantify the risk. This will be dependent on how many patients attending the practice were already infected (and can therefore act as a source of virus for onwards transmission), the nature of the procedures undertaken on individual patients, and the precise failures of infection control practice.

“It is worth pointing out that if a random 22,000 adults from England were to be tested for hepatitis C infection, approximately 100 cases would be found – the prevalence of infection is roughly 0.5%. Thus, it is inevitable that the testing programme will identify a number of patients who have chronic HCV infection. However, those individuals may well have acquired their infection through other routes, so the question will then be whether or not it is possible to identify linked cases of transmission. This is done by phylogenetics, but the data are complex and require careful interpretation.

“The prevalence of chronic HBV infection is probably slightly lower than that of HCV, so I would expect fewer cases of HBV infection to be discovered.

“Also worth noting is that it is definitely in the patients’ interests to know if they are infected with any of these viruses, as treatment is possible for all three, and indeed, new developments in the therapy of chronic HCV infection can result in viral clearance in almost all patients.”

Dr Marcus Dorner, Non-Clinical Lecturer in Immunology, Imperial College London, said:

“The risk of exposure of a large number of patients to HIV, hepatitis B or hepatitis C is very low since the dentist himself was not infected. However, the lack of proper procedures leading to the use of instruments potentially contaminated with blood from previous patients raises concern. The likelihood of contracting hepatitis B, hepatitis C or HIV from dental procedures involving cuts, drilling or other invasive means cannot be neglected.

“Hepatitis B virus is by far the most infectious virus of the three viruses mentioned, resulting in an approximately 6-30% chance of transmission by direct blood contact (only if blood contact occurs – we do not yet know whether any blood contact has occurred in this case), depending on the viral strain. Hepatitis C virus is less stable, resulting in likelihoods of infection around 1-2% when exposed (again we don’t know if there has been any exposure) whereas HIV is hardest to transmit, resulting in a risk of infection of 0.1%. These values are from historical cohorts of needlestick injuries in hospital settings but given that dental procedures were performed without adequate barrier maintenance the risk to patients might be comparable if exposure occurred.”

Dr Jonathan Stoye, Head of Division of Virology, MRC National Institute for Medical Research (NIMR), said:

“With the introduction of routine hepatitis B virus vaccination, cases of dentist to patient transmission have essentially disappeared.  Now the main source of infectious virus encountered in a dental surgery is likely to be a patient unknowingly carrying such a blood borne virus.  If standard infection control procedures such as instrument sterilization are not observed there is then the possibility of virus transfer to subsequent patients on used instruments.  Such a risk is very small but not zero.  The only way to rule out infection is by blood testing.”

Dr Ben Neuman, Lecturer in Virology, University of Reading, said:

“Dentistry can be bloody work.  If instruments are not sterilised properly between patients, there is a small risk that a dentist could transfer a bit of blood including a blood-borne virus from one patient to another without realising it.  Dental instruments are designed to be corrosion resistant and inhospitable to microbes, so the risk remains low, but it is good to see the NHS taking a proactive approach to patient safety in this case.

“Even viruses as potentially life threatening as hepatitis B and C do not always cause a person to become noticeably ill.  I suspect that they will find a few viruses in a group as large as this if they look hard enough, but there are other ways to catch viruses, and it may be difficult to pin any infections specifically on a bad visit to the dentist years ago.”

Prof Jonathan Ball, Professor of Molecular Virology, University of Nottingham, said:

“There are very strict procedures in place to protect patients from possible cross-infection by blood-borne viruses, such as hepatitis C, hepatitis B and HIV, during dental procedures and it appears that these weren’t being followed by this dentist.

“The dentist tested negative for these viruses, so it seems that the real concern is that lapses in infection control measures might have put people at risk from cross-infection from other patients potentially infected with a virus.

“The prevalence of these infections in the general population is low and the transmission risk from most dental procedures would also be low, but the risk is still real and so it is right for the NHS to screen. This won’t be easy as the dentist has been treating patients for decades.

“If any of the patients recalled do test positive for any virus then it won’t be clear where their virus came from; and trying to work that out will be a huge scientific detective task.”

* http://www.england.nhs.uk/2014/11/12/dental-recall/

Declared interests

None declared