The Florida Department of Health and Rehabilitative Services (HRS) and the Centers for Disease Control and Prevention (CDC) have previously described six patients who acquired human immunodeficiency virus (HIV) infection while receiving care from a dentist with HIV infection [1-6]. To date, this dentist's practice is the only practice of a health care worker with HIV infection in which HIV transmission to patients has occurred and has been reported. The events that resulted in the infection of these patients remain unknown; however, the available evidence suggests that HIV was transmitted from dentist to patient rather than from patient to patient [7]. In July 1991, Miami newspapers published the name of another dentist who had been diagnosed with the acquired immunodeficiency syndrome (AIDS). This dentist had closed his practice 2 months earlier because of ill health. To determine whether HIV had been transmitted to patients during receipt of care in this practice, we investigated the dentist's medical history, his dental practice, and his former patients. Methods Epidemiologic Investigation Information about the dentist's health was obtained from his available medical records. Because the dentist was too ill to be interviewed, information about his practice was obtained by interviewing his two former employees, a dental assistant and an office manager. The dentist's spouse provided HRS with the names and addresses of those persons who had been patients of the dentist during the last 5 years of his practice; HRS sent a letter to each of these patients telling them that they had received care from a dentist with HIV infection and providing them with information about HIV counseling and testing services. We reviewed the available dental and medical records of all patients with HIV infection, and we interviewed all living patients infected with HIV to determine whether they had behavioral or transfusion risk factors for HIV infection. Laboratory Investigation We obtained a blood sample from the dentist with his consent. Blood samples were also collected from all consenting patients with HIV infection and from those of the patient's sexual partners who were known to be infected with HIV. Mononuclear cells were separated from the samples and DNA was extracted as previously described [8]. The primers MK603 and CO602 were used in a polymerase chain reaction for primary amplification of approximately 1500 nucleotides of the C1 to gp41 domain of the HIV-1 envelope gene [9]. The primary amplified DNA was then diluted 50-fold and used in a nested polymerase chain reaction with the primers CL207 and CO72 to reamplify approximately 700 nucleotides of the C2 to C5 region [4]. The reamplified DNA was purified by the Qiagen PCR Purification Spin Kit (Qiagen Inc., Chatsworth, California), and approximately 300 nucleotides of the V3 and flanking regions were sequenced in an automated DNA sequencer (Applied Biosystems Inc., Foster City, California), either directly or after being cloned into an M13 vector [4, 9]. Genetic analysis was done on direct sequences from the dentist, 21 patients, and 2 sexual partners of patients. Direct sequencing of DNA from its polymerase chain reaction product identifies the most common nucleotide at each position from all the variants present within a person. Only cloned sequences could be obtained from patients R, L, and P. A consensus sequence was generated for patients L (10 clones) and R (5 clones) based on the nucleotide present at each position in at least 50% of the clones. Because patient P had only three clones, it was difficult to generate a consensus sequence; thus, the longest, most representative clone sequence was chosen for analysis. Sequences were aligned by hand using ESEE2.00B [10]; sequence positions that could not be aligned, as well as those in which one sequence had an undetermined base, were eliminated from the analysis. Two hundred fifteen alignable positions were used in phylogenetic analysis. We calculated the number of base substitutions between each of the sequences being compared to obtain a measure of the pairwise genetic distances between the viruses of the persons studied. These distances were used to construct a phylogenetic tree. Programs from the PHYLIP suite, version 3.4, for Unix were used to construct the neighbor-joining bootstrap tree shown in Figure 1 [11]. SEQBOOT was used to create 1000 subreplicate sequence files; DNADIST returned a distance matrix from each file, using a maximum-likelihood multiple-hit correction; NEIGHBOR was used to construct a neighbor-joining distance tree from each distance matrix; and CONSENSE determined the percentage of replicate trees in which each internal branch was present. This percentage, or bootstrap proportion, shows how strongly phylogenetic analysis supports a particular grouping of sequences. Figure 1. Unrooted phylogenetic tree illustrating the relations among HIV sequences obtained from the dentist, 24 of his former dental patients, and 2 sexual partners of patients. Results The dentist was a man in his 60s who had known behavioral risk factors for HIV infection and had had a positive HIV antibody test in June 1988. The reason for testing at that time is not known; the dentist had no record of an earlier negative test. In November 1989, he was asymptomatic and had a CD4+ T-lymphocyte count of 206 cells/L. By May 1990, his CD4+ lymphocyte count had dropped to 69 cells/L and therapy with zidovudine and aerosol pentamidine was started. In March 1991, he was hospitalized with pneumonia of unknown cause that responded to therapy with dapsone and trimethoprim. Human immunodeficiency virus encephalopathy was also diagnosed, although a magnetic resonance imaging scan was normal. In May 1991, the dentist was hospitalized after a syncopal episode in his office. At admission, he stated that he had retired 3 months earlier, but he apparently continued to provide care for a small number of patients. According to his medical records, his recent memory was impaired; a magnetic resonance imaging scan done at this time was normal. After he was discharged from the hospital, he closed the remainder of his practice. A month later, he was hospitalized with diagnoses of staphylococcal sepsis, anemia, and HIV encephalopathy. He died in a hospice in August 1991. The dentist had practiced in the Liberty City area of Miami, Florida, for almost 30 years and primarily served an indigent patient population. According to his staff, he saw approximately 15 to 20 patients on a typical day and did extractions for about 5 patients per day. Since 1986 or 1987, he had routinely worn gloves, a mask, and eye protection. He recapped needles using a two-handed technique. Surgical instruments were autoclaved and other instruments, such as curettes and instruments used in restorative dentistry, were immersed in a liquid chemical germicide called Cetylcide, which is a quaternary ammonium compound (use of trade names is for identification only and does not imply endorsement by the Public Health Service or the U.S. Department of Health and Human Services). Dental handpieces were wiped with alcohol but were not autoclaved. Single-use, disposable pieces of equipment, such as prophylaxis cups, were occasionally reused after being immersed in Cetylcide. Handpiece and dental unit water lines were not flushed. Both staff members reported that they had tested negative for HIV infection. Of the 6474 letters sent to former patients of the dentist, 5469 (84.5%) were delivered. As a result of these letters and of newspaper articles and other media coverage about the dentist, 1279 patients were found to have been tested for HIV infection. Of these patients, 24 (1.9%) were seropositive. Additional case-finding activities identified another 4 former patients who were infected with HIV or who had AIDS. Thus, a total of 28 former dental patients with HIV infection (designated A, B, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z, BB, CC, and DD) were identified. Sixteen of the 28 infected patients (57%) were female. The patients ranged in age from 17 to 69 years (median, 35 years); 26 were African-American, 1 was Hispanic, and 1 was Caucasian. Five patients (H, U, X, CC, and DD) died of AIDS before or during the investigation. Based on interviews with the patients and review of their medical records, we placed patients in a mutually exclusive hierarchy of potential risk categories for HIV infection (Table 1). Although none of the men acknowledged having practiced homosexual or bisexual behaviors, 19 patients had engaged in drug use or in sexual behaviors that could have resulted in HIV infection. An additional 5 patients had had one or more sexually transmitted diseases. Only 4 patients could not be placed in a potential risk category. Table 1. Potential Risk Factors among Patients with HIV Infection in a Florida Dental Practice According to dental records, which were available for 22 patients, or self-report, all but 4 of the 28 patients infected with HIV had received care from the dentist in 1988 or later, years during which the dentist was known to have had HIV infection. During this time, 18 of the patients infected with HIV had a total of 24 invasive procedures documented in their dental records (Table 2). In most cases, the invasive procedure was extraction or alveoplasty; none of the documented procedures required the intraoral use of a dental handpiece. In March 1988, patients Z and BB had extractions done on the same day; this was the only common visit day recorded. Table 2. Dates on Which Invasive Procedures Were Documented in Patient Dental Records Blood samples were obtained from the dentist and 24 of his former patients. One of these patients, patient H, died during the investigation, after a blood sample was collected. Three other patients (X, CC, and DD) died before their blood samples could be collected. The blood sample from patient U was
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