Four cases of transmission

There have only ever been four documented cases of HIV transmission from healthcare workers to patients, though in all but one of these the exact route of transmission remains unclear. There has never been a case in the UK.

The most recent was reported from Spain in 2006.¹ In this case a female patient was infected by an obstetrician when he performed an emergency caesarean on her in 2004.

The woman came down with a feverish illness and showed signs of immune-system disturbance two weeks after her caesarean, and eight weeks later she tested positive for HIV. Neither her husband nor baby had HIV and she reported no other risk factors.

The surgeon, a gay man, did not know he had HIV and had never been tested. After it was realised he might have infected his patient, he said he recalled pricking his finger on a needle during the operation. He took an HIV test, which was positive, seven months after the caesarean.

Phylogenetic analysis of the HIV of both doctor and patient revealed that the viruses they had only differed by 3%, whereas three unrelated samples taken for comparison were different by 23%.

This is the first case where there appears to be relatively strong evidence for the exact route of transmission.

The three previous transmissions of HIV from a healthcare worker to a patient were:

• The ‘Florida dentist’, David Acer, who in 1990, somehow infected six of his patients.
• A French surgeon who transmitted HIV to an elderly patient during a hip replacement operation in 1992.
• A French nurse who transmitted HIV to a patient during a hospital stay in May 1996, though it’s not known exactly how.

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 initially identified as the source of infection for five of his patients. (A report from the CDC in 1993 subsequently presented evidence of a sixth.²) Infection was argued to have occurred during 1988 to 1989.³ 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 the 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.

The author of the original report on the case explained that all five patients identified at that time 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.⁴ 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.

Subsequent analyses by another team have called into question a conclusive link between all the patients and the dentist.^{5 6} They argued that the similarity in viral isolates was not conclusive. In their own study, DeBry 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 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.^{7 8}

In 1997 French health authorities reported that an orthopaedic surgeon who had tested HIV-positive in 1994 had infected a patient during a lengthy hip-replacement and bone graft operation which took place in 1992.⁹ The surgeon himself appeared to have been infected by a patient during an operation in 1983. Neither patient nor surgeon had any other known risk factors for HIV, and genetic sequences from the viruses of the surgeon and the patient were almost identical. The patient was the only positive diagnosis in 983 of the surgeon’s former patients tested. Investigation of the surgeon’s work practices revealed that he was in the habit of several practices that could have caused injuries such as palpating the needle tip when sewing up operation incisions and twisting sharp suture wires with his fingers.

A 61-year-old patient who had been admitted for surgery in May 1996 developed primary HIV infection the following month.¹⁰  No surgeons on the team were found to have HIV but two nurses who had cared for the patient were HIV-positive. One, a Zairean man, was ruled out on the basis of phylogenetic analysis. The source therefore appeared to be a 51-year-old female nurse, who was unaware of her HIV infection until, in June 1996, she was also hospitalised for hepatic insufficiency. A diagnosis of infection with both hepatitis C virus and HIV was established. HIV viral load was 1.8 × 105 copies/ml and her CD4 cell count was 94 cells/mm³.

Although the paper authors point out that “patient and nurse 2 might have independently acquired similar geographic local variants” of HIV, the nurse’s low CD4 count implies longstanding HIV infection. However the nurse did not perform exposure-prone procedures such as venepunture on the patient and there is no indication of how transmission might have happened in this case.