Transmission reported in one dental practice: The Florida Dentist

One episode where transmission from a dentist to his patients is believed to have occurred has been reported. A dentist in the United States was identified as the source of infection for six of his patients. Infection was argued to have occurred during 1988–89 (Cieselski). This conclusion was reached after examining the DNA sequences of viral isolates from all patients found to be HIV–positive.

A very close correlation was found between the viral DNA of five patients and that of the dentist. In contrast, two other patients with other risk factors for HIV infection showed markedly different viral DNA patterns, as did 35 control samples taken at random from HIV–positive people in the same district.

Dentist doubted as source of infection

Subsequent analyses by another team have called into question a conclusive link between all five patients and the dentist (De Bry; Weiss). They argued that the similarity in viral isolates was not conclusive. In their own study De Bry and Weiss had recruited a control group of seropositive individuals who lived in the same area. Many of the control group recruited in the catchment area of the dental practice showed enough similarities in the genetic structure of their HIV isolates to cast doubt on the dentist as the irrefutable source. However, it should be borne in mind that HIV evolves rapidly, generating a mixed population of subtypes within each individual. The analysis of HIV genomes is still a new and experimental field, so scientific debate on the methodology for establishing sources of infection is likely to continue.

DeBry also argued that the exposure risk evidence of the five patients was open to question, since they were all aware of the dental transmission hypothesis (and by implication, could have falsified their accounts in order to make themselves eligible for compensation).

A subsequent investigation conducted on behalf of an insurance company has reported that all the patients may have had other risks for HIV infection which were not disclosed to the CDC investigators. Although this claim has been strongly refuted by the CDC, questions still hang over this unusual case.

For example, it is not clear from the insurance records of one of the infected patients whether she was ever treated by Dr Acer, and her insurance records do not tally with the information later provided to the CDC investigation. Indeed, her records suggest that she first visited the surgery nearly a year after the CDC investigators were told she first attended the practice.

A particularly unusual aspect of these cases is the very rapid development of symptoms following infection in some patients – in one case just 17 months after the assumed date of infection. This might have happened for several reasons. HIV infection through blood often leads to the development of AIDS more quickly. It may also be the case that patients were infected with an especially virulent strain of HIV, leading to faster disease progression. However, this question has not been addressed in any detail by the investigations which have taken place.

The case remains full of inconsistencies which are summarised and debated in two articles published by the Annals of Internal Medicine in 1996 (Barr; Brown).

How did transmission occur in this dental practice?

Cieselski reported that all five patients had invasive dental work after the dentist was diagnosed with AIDS and had evidence of severe immunosuppression. There were many opportunities for the dentist to have injured himself during invasive procedures such as tooth extractions (Lewis). Contrary to claims made in a BBC TV Panorama documentary, these injuries are common in dental practice.

All five patients received multiple injections of local anaesthetic, and sharps injury during anaesthetic administration could have resulted in contamination of the syringe apparatus with the dentist's blood, after which additional anaesthetic may have been injected into the same patient. A sharps injury could also result in direct contact of the dentist's blood with the patient's inflamed or damaged oral tissues during the invasive procedures. Although the dentist began to wear gloves routinely in 1987, gloves do not prevent most injuries caused by sharp instruments. Instruments were cleaned in accordance with guidelines intended to prevent HIV transmission after early 1987.

Instruments such as a high-speed dental handpiece, which might have facilitated cross–infection between patients (assuming, of course, that the dentist had first of all infected one of the patients) do not appear to have been used on two HIV infected patients on the same day. Researchers reached this conclusion after examining the appointments book of the practice. If contaminated instruments or equipment are assumed to have been the route of transmission, one would expect to see a clustering of appointments of infected patients. However, it has been suggested that the dentist was treating HIV–positive patients who were his sexual partners (and therefore likely to be infected with the same strain of HIV) out of clinic hours. No official investigation has yet been able to substantiate this claim, or to correlate any alleged `ghost' appointments with those of subsequently infected patients.

Another potential source of transmission remains uncertain, since it depends on anecdotal evidence. A practice nurse told investigators that the dentist was in the habit of cauterising his own mouth ulcers with dental instruments on an almost daily basis. CDC investigators remain uncertain as to whether these highly unhygienic episodes of self–treatment coincided with periods during which the HIV–infected patients were treated, and in their 1992 report suggested that sharps injuries were a more likely route of transmission.

Another school of thought, not addressed by the CDC investigation, takes the view that the infection of the six patients was deliberately planned and executed by the dentist, although there is no clear motive.

Lessons of this case concerning risks from invasive procedures

Whilst the CDC investigation points clearly to the potential risk attached to sharps injuries, there is considerable disagreement amongst dental experts over the risk posed by the inadequate sterilisation of dental equipment. A 1992 study showed that potentially infectious quantities of HIV may be present in water lines and other dental equipment not normally sterilised between each patient (Lewis).

Critics of Lewis's study point out that concentrations of HIV far in excess of those likely to be present in blood were used in combination with inadequate disinfectants, combining to give a misleading picture of the likelihood of infection because of inadequate cleaning of instruments. They also note that the failure to practise universal precautions, especially in regard to compliance with safety procedures for needle and glove use, continue to constitute a far greater area of risk than already adopted sterilisation procedures.

Whilst doubts about the dental transmission study persist amongst some experts, it is important to strike a balance between being overly cautious about the risks of HIV transmission through surgical accidents, and being less than cautious. The former is likely to result in panic; the latter in failures to observe sensible precautions.

Does this case show a potential risk of HIV infection through dental treatment?

The chief questions raised by this case are:

• Was the dentist the source of infection?
• Were dental handpieces the route of infection, and if so, how easily can they transmit HIV?

The answer to the first question is now widely agreed to be `yes'. The second question remains debatable. It is by no means clear either that dental handpieces were the route of infection, or that they may harbour potentially infectious quantities of HIV despite autoclaving. Nevertheless, it seems clear that greater adherence to infection control guidelines is the only way to prevent a repetition of this incident and to allay fears of a repetition.

References

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