Clarke, Christina A. PhD; Glaser, Sally L. PhD
Dramatically increased occurrences of Kaposi sarcoma (KS) 1 and non-Hodgkin lymphoma (NHL) 2 in the early 1980s were among the first clinical observations leading to the characterization of AIDS, now known to be caused by infection with HIV. Subsequently, data from clinical series, HIV-infected cohorts, and AIDS cancer registry linkages made it clear that HIV-infected persons also had a marked excess of other malignancies, including Hodgkin lymphoma (HL), lip and lung cancers, and cancers of the cervix and anus, among others. 3–5 Since late 1995, highly active antiretroviral therapy (HAART) has effected change in the clinical and epidemiologic features of HIV-associated malignancies, notably decreases in the incidence of KS and, to a lesser extent, NHL. 6–8 However, long-term trends in HIV-associated malignancies are uncertain, particularly as some cancers have not shown post-HAART incidence declines and risks of others might be expected to increase with duration of the moderate immunodeficiency permitted by HAART. 9
Throughout the HIV epidemic in the United States, timely questions about trends in HIV-associated malignancies have been challenging to address because of lack of access to the appropriate data. Hospital-based or other clinical case series have useful detail on patient clinical status but typically are of unknown representativeness and inadequate size for reliable detection of moderate incidence changes. 10 Case series from population-based AIDS or cancer registries are generally larger and more representative but also have limitations for ongoing surveillance: AIDS registries collect information only about the AIDS-defining cancers (KS, NHL, cervical cancer) and may not detect them when they occur after an initial AIDS diagnosis 11; cancer registries, while reasonably complete (85–90%) for HIV-associated malignancies, 12 are presently ill-equipped to monitor them because information about HIV status is not systematically obtained. While some cancer registry–based surveillance of HIV-associated cancer has been carried out using surrogates for high-risk populations (e.g., never-married men, 13,14 San Francisco county residents 13–16), most comprehensive studies of the temporal and absolute associations of AIDS and cancer 3,4,17 have involved record linkages between population-based cancer and AIDS registries. However, these linkages are not conducted routinely, and little is known about their quality in populations using HAART, for whom AIDS is a poorer proxy for HIV-positive status. 18,19 An alternative resource for linkage-based studies of HIV-associated cancers is population-based HIV registries, used successfully in Australia. 18,20 However, in many US states, including California, and many European countries, the utility of these registries for linkages may be limited by confidentiality practices, such as those precluding collection of patient names.
A sound and feasible mechanism for the timely detection of changes in HIV-associated malignancies remains an important goal for public health surveillance. Recognizing the potential of population-based cancer registries in this regard, we sought to determine the utility of cancer registry–available information for the classification of HIV-associated cancers. Toward this end, we assessed the completeness and quality of registry-available and linkage-based indicators of patient HIV status for NHL, HL, and anal cancer patients reported to the population-based cancer registry in the Greater San Francisco Bay Area, an epicenter of the HIV epidemic. The ultimate goal of the study was to develop a strategy for the classification of HIV-associated cancers useful for regional surveillance efforts.
We identified eligible cases from the Greater Bay Area Cancer Registry (GBACR), a participant in both the National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) program and the state-supported California Cancer Registry. We focused our attention on NHL, HL, and anal cancers for 2 reasons. First, in this population, information on patient HIV status is not necessary for the epidemiologic study of KS, which is almost always HIV associated; and second, yearly surveillance is unproductive for cancers with low incidence (e.g., lip cancer, with <10 cases diagnosed per year) or low expected proportions of HIV-associated cases (e.g, cervical, lung cancers). Thereby, eligible for this study were new diagnoses of NHL (ICD-O-2 histology codes 9590-9595, 9670-9698, 9702-9714), HL (histologic codes 9650-9667), and invasive anal cancer (site codes C21.0-21.8, histology codes 8000-8720) occurring in any person living in the 9 registry-area counties of Northern California (Alameda, Contra Costa, Marin, Monterey, San Francisco, San Benito, San Mateo, Santa Clara, Santa Cruz) between January 1, 1990 and December 31, 1998, the most recent date with complete registry data when this study began. Altogether, 12,384 diagnoses were available for study, including 10,126 NHLs, 1497 HLs, and 895 anal cancer diagnoses. Fewer than 1% of these diagnoses were made exclusively from the death certificate. All procedures were approved by the Institutional Review Board of the Northern California Cancer Center.
Completeness of GBACR for HIV-Defining Cancers
Prior linkages of GBACR and San Francisco AIDS registry patient records suggest that the cancer registry is mostly complete for AIDS-defining cancers. The most recent linkage, conducted in 1996 as part of the National AIDS Cancer Registry Match, found that the GBACR had identified 90% of all AIDS cancer patients reported to the San Francisco county AIDS registry. However, completeness varied slightly by tumor type, being 93% for immunoblastic NHL, for which the GBACR identified 1052 of 1136 cases in either the GBACR or the AIDS registry, 88% for Burkitt lymphoma (486/549), 86% for KS (5694/6634), and 85% for primary lymphoma of the brain (320/377).
Sources and Indicators of HIV Status
For this study, we retrieved HIV information for each patient from 3 independent sources (cancer registry records, death records, AIDS registry). From the 2 cancer registry–available sources (cancer registry records, death records), we obtained a maximum of 5 indicators of HIV status. From cancer registry records, the 3 indicators were the SEER HIV/AIDS variable (collected as part of the extent of disease field for lymphomas and KS since 1990), a report of diagnosis with KS (occurring any time before or after diagnosis with the index cancer), and any mention of HIV or AIDS status on the hard-copy registry abstract. The SEER HIV/AIDS variable (hereafter referred to as the HIV/AIDS flag) reflects status at time of cancer diagnosis, as it is coded directly from the medical record at the time of initial case report and is not corrected for any subsequent follow-up information (e.g., cause of death from the death certificate). From registry-available death records, the 2 indicators were an underlying cause of death coded as HIV/AIDS (ICD-9 codes 42-44 or ICD-10 codes B20-B24) and any mention of HIV or AIDS status on the hard-copy death certificate for cancer patients whose cancer registry vital status indicated that death occurred prior to or on December 31, 1999. From the 3rd source, the California state AIDS registry, we obtained patient AIDS status via record linkage, as described below.
The HIV/AIDS flag, KS report, and cause of death were available as electronic data from the GBACR database. This database includes demographic and tumor information abstracted directly from the medical record and vital status and cause of death information obtained annually from routine linkages with state and national vital statistics records. Mention of HIV or AIDS status on the registry abstracts and death certificates was sought via manual review of paper documents by 2 trained coders who examined each document for definitive or presumptive evidence of HIV-positive status, as delineated in Table 1. For some patients, these indicators could not be assigned because of missing or illegible documents. Finally, an electronic file containing patient identifiers and registry variables, as well as information on all registry HIV indicators, was matched with the California state AIDS registry in May 2002, using Automatch (Matchware Technologies, Inc., Silver Spring, MD) probabilistic linkage software aided by manual review and resolution of all possible matches.
Several features of determining HIV status in the cancer registry setting impacted our strategy to assess the quality of registry-available HIV status indicators. First, validation of indicators against a gold standard, i.e., serologic confirmation, would be exceedingly difficult to accomplish in a retrospective, population-based setting. Therefore, we aimed to understand the quality of registry HIV status indicators using existing data. To accomplish this, we assumed that patients who had positive indicators from at least 2 of the 3 independent sources (i.e., registry, death, or linkage) represented true HIV-positive patients, and that the probable validity of HIV status identified by only 1 source could be gauged by assessing the joint probabilities of positive status across indicators. Second, HIV-negative status is generally not recorded in the medical record for persons without HIV infection. Therefore, we characterized HIV status as the presence or absence of evidence of HIV-positive status, grouping known negative and unknown status. This characterization precluded using common measures for validity or agreement, including sensitivity/specificity or the kappa statistic. Third, some indicators of HIV status were limited to certain clinical categories of patients. Thus, only deceased persons were eligible for indicators from death sources; only HIV-positive cancer patients who developed KS were eligible to have a KS report in the cancer registry; and HIV-positive persons with anal cancer and HL who never developed AIDS were ineligible for inclusion in the AIDS registry. Because of these issues, we designed this analysis to document the completeness of each individual HIV indicator, to compare the comprehensiveness of all 6; to document the number of sources identifying patients with any positive status, to compare their respective utility; and to measure the joint probabilities of positive status between pairs of indicators, to provide crude estimates of indicator validity.
Cross-tabulations were used to assess the number of patients with evidence of positive HIV status by indicator type (HIV/AIDS flag, abstract mention, KS report, cause of death, death certificate mention, linkage), indicator source (registry, death, linkage), and by the total number of indicator sources identifying each patient (minimum of 1, maximum of 3), as well as the joint probabilities of positive status across each pair of indicators. This last measure was quantified by calculating the percentage of all cases with positive status for 1 indicator among all cases who had positive status for the second. All pairwise comparisons involving indicators from death sources were limited to deceased persons. Calculations were carried out separately for each cancer site under study and were performed using SAS, version 6.12 (SAS Institute, Cary, NC).
Demographic characteristics of the study sample reflected cancer site–specific characteristics and the multiethnic population of the Greater San Francisco Bay Area. Among all patients with NHL, 60% were male; 62% were aged 55 years or older; 71% were non-Hispanic white, 10% Hispanic, 6% African-American, 10% Asian/Pacific Islander, and 3% of other or unknown race/ethnicity; 23% were from San Francisco County; and 62% were reported to the cancer registry as deceased by the aforementioned date. Among all HL patients, 55% were male; 22% were aged 55 or older; 69% were non-Hispanic white, 14% Hispanic, 8% African-American, 6% Asian/Pacific Islander, and 2% were of other or unknown race/ethnicity; 16% lived in San Francisco county; and 25% were reported as deceased. Among all patients with anal cancer, 56% were male; 55% were aged 55 or older; 74% were white, non-Hispanic, 10% African-American, 9% Hispanic, 5% Asian/Pacific Islander, and 2% were of other or unknown race/ethnicity; 31% lived in San Francisco county; and 45% were reported to the cancer registry as deceased.
Completeness and Comparisons of HIV Indicators for NHL Patients
Table 2 shows the completeness of each indicator for all NHL patients. Overall, nearly 20% (n = 1978) had at least 1 positive indicator of HIV/AIDS; the single most informative indicator was the HIV/AIDS flag. Among the 3 sources, we found more definitive or presumptive evidence of HIV-positive status from a cancer registry source (n = 1843) than from a death source (n = 1501) or from linkage with the AIDS registry (n = 1489). As shown in Table 3, a majority (65%) of the 1978 HIV-positive NHL patients were identified on the basis of all 3 sources, 18% by 2 sources, and 17% by 1 source only. Those with data from only 1 source were mostly identified from a cancer registry source. Fewer than 1% of HIV-positive patients (n = 13) were identified exclusively from linkage with the AIDS registry.
To identify any indicator of questionable reliability, we examined the pairwise distributions of positive status for each individual indicator of HIV-positive NHL. Most indicators shared high probabilities of positive status with each other, with the exception of presumptive death certificate evidence. The HIV/AIDS flag was positive in 95% of NHL cases with other positive registry indicators, including a definitive registry abstract mention or a registry report of KS, and also was positive in at least 91% of cases with positive cause of death (91%), definitive death certificate mention (92%), or AIDS registry match (91%) indicators. However, the HIV/AIDS flag was unlikely to be positive (15%) in the 87 patients with presumptive death certificate mention of HIV. The definitive abstract mention indicator was positive in at least 87% of NHL cases with other positive indicators (data not shown) except presumptive death certificate mention (25%). Although KS was recorded in the cancer registry for <20% of the NHL patients, the majority of these 378 patients also had a positive HIV/AIDS flag (95%), definitive registry abstract mention (99%), presumptive abstract mention (94%), underlying cause of death (90%), definitive death certificate mention (98%), or matched with the AIDS registry (88%). Among all deceased NHL patients for whom cause of death was known and a death certificate could be obtained, 99% of 1262 with an HIV/AIDS underlying cause of death also had a definitive death certificate mention; however, the converse was true for only 88% of 1424 patients with definitive death certificate mention, suggesting some discrepancy in the coding of cause of death. In addition, a positive cause of death or definitive death certificate mention was found in at least 84% of deceased NHL patients with positive registry or match indicators (data not shown), with the exception of presumptive abstract mention (29%). The AIDS registry match indicator was positive in at least 78% of patients with positive registry or death indicators; however, only 67% of patients with a presumptive abstract mention and 22% with a presumptive death certificate mention had a positive AIDS match. Eighty-eight percent of NHL patients with KS and 90% of NHL patients with death certificate mention of HIV/AIDS matched with the AIDS registry.
Completeness and Comparisons of HIV Indicators for HL Patients
For HL, which is not an AIDS-defining cancer and for which proportionately fewer cases were deceased than for NHL, completeness and results of comparisons between HIV indicators were different. Table 2 shows the completeness of each indicator for HL patients. Only 8% of all patients had any positive HIV evidence. Nearly twice as many had positive evidence from a cancer registry source (n = 105) as from a death source (n = 53) or from the linkage (n = 56), and the HIV/AIDS flag was the most informative indicator. Table 3 shows that 35% of HL patients with any HIV-positive evidence were identified by all 3 sources, 18% by 2 sources, and nearly half (48%) on the basis of 1 source only, overwhelmingly cancer registry information. Only 1 HL patient (<1%) was identified exclusively by the linkage.
Comparisons of individual indicators in HL patients showed that the HIV/AIDS flag, definitive abstract mention, and definitive death certificate mention indicators generally demonstrated high probabilities of positive status with each other. Deceased patients with positive registry indicators (HIV/AIDS flag, definitive abstract mention) were only moderately likely (51–58%) to have positive status for the cause of death indicator, although they were very likely (85–88%) to have definitive mention on the death certificate. The presumptive death certificate mention indicator was positive for only 1 patient who did not have positive evidence from any other indicator. The 56 HL patients who matched with the AIDS registry were likely to have a positive HIV/AIDS flag (77%), definitive abstract mention (74%), cause of death (81%), and definitive death certificate mention (92%). Conversely, the proportions of HL patients with positive evidence from these indicators who also matched with the AIDS registry were lower (44–52%), reflecting the middling proportion (49%) of patients with any positive indicator who matched with the AIDS registry.
Completeness and Comparisons of HIV Indicators for Anal Cancer Patients
Completeness of HIV indicators for anal cancer patients was generally similar to those for HL (Table 2). Overall, 168 patients (18%) with anal cancer, a non-AIDS-defining cancer, had evidence of HIV-positive status on the basis of at least 1 of the 6 indicators, and the single most informative indicator was the registry abstract. Consequently, although the HIV/AIDS flag is not collected for anal cancer patients, more patients had HIV/AIDS evidence from a cancer registry source (n = 138) than from a death source (n = 75) or from the linkage (n = 85). Table 3 shows that about half of all anal cancer patients with any HIV evidence were identified by multiple sources, 21% by 2, and 29% by all 3 sources. Fifty-two percent of patients were identified by 1 source only, mostly registry abstract information. However, in comparison to NHL and HL cases, larger proportions of anal cancers were identified as HIV positive solely on the basis of death information (9%) or the linkage (5%).
Interindicator concordance was wider in anal cancer patients than in NHL or HL patients. About half of the 110 anal cancer patients with definitive abstract mention of HIV/AIDS had positive status for match (52%) and cause of death (56%) indicators, although they were very likely to have definitive mention on the death certificate (90%). Patients with a presumptive abstract mention showed variable levels of positive status for other indicators. Thirty-five percent of patients matched with the AIDS registry; deceased patients were likely to have definitive mention on the death certificate (86%) but less likely to have an HIV/AIDS cause of death (50%). Anal cancer patients with the KS indicator were likely to have other positive registry and death indicators (data not shown), but only 62% of these 21 matched with the AIDS registry. In deceased patients with other registry and match evidence, most (86–100%) had definitive mention of HIV/AIDS on the death certificate. One hundred percent of patients with an HIV/AIDS underlying cause of death had a definitive death certificate mention, but the converse was true for only 67% of patients, providing more evidence for nonuniformity in the coding of underlying cause of death. The presumptive death certificate mention indicator was positive for only 1 patient and thereby could not be compared effectively. Patients who matched with the AIDS registry were likely to have a definitive death certificate mention (91%) but less likely to have definitive abstract mention (70%) or an HIV/AIDS cause of death (63%).
Development of a Classification Strategy
The majority of presumed HIV-positive NHL patients (83%) and at least half of HL and anal cancer patients were identified by multiple sources of HIV indicators (Table 3). Acceptable levels of agreement were demonstrated between most pairs of individual indicators, except for presumptive abstract mention, which shared middling levels of positive status across all sites, and presumptive death certificate mention, which was uncommon for HL and anal cancer patients but was unlikely to be positive in NHL patients with other positive evidence. Thus, it seemed prudent to exclude presumptive indicators of HIV-positive status from a registry-based classification scheme for HIV-associated NHL, HL, and anal cancer.
As both the manual review of registry abstracts and death certificates, and record linkages with AIDS registries, are time-consuming processes, we also evaluated the mode of identification (electronic, manual review, linkage) for patients with evidence of HIV-positive status, but excluding patients with presumptive evidence only (Table 4). For presumed HIV-positive NHL patients, 98% were ascertained by at least 1 electronic, registry-based indicator. For HIV-positive HL patients, 92% were identified by at least 1 electronic indicator, while manual review ascertained 8% of patients. However, for anal cancer, the manual review identified the majority of patients (54%), electronic indicators identified a smaller proportion (38%), and linkage alone identified 7%.
These results suggest that reasonable strategies for the cancer registry–based classification of HIV-associated cancers differ for NHL, HL, and anal cancer. For NHL and HL patients, evidence from any electronic indicators (HIV/AIDS flag, KS report, underlying cause of death) should identify the great majority of HIV-positive cases with accuracy and efficiency. However, for anal cancer, manual review should be conducted to identify HIV-associated patients and used in addition to electronic information; AIDS registry linkage information should be considered optional.
This study of HIV status information routinely available for NHL, HL, and anal cancer patients in our population-based cancer registry has demonstrated that available registry and death indicators are useful in classifying HIV status in cancer registry patients. Our results show that the combination of 5 cancer registry–available indicators of HIV status identified 25% more NHL patients and nearly 50% more HL and anal cancer patients than were detected by linkage with the state AIDS registry. Furthermore, patients identified as HIV/AIDS positive by registry-available indicators included nearly all of the patients identified through AIDS registry linkage (99% of NHL and HL and 93% of anal cancer). These observations suggest that, compared with the linkage-based mode of classification, cancer registry–available indicators are of sufficient completeness to classify the HIV status of NHL, HL, and anal cancer patients. While the validity of cancer-registry indicators could only be approximated in these data, we did not uncover any contraindication to using the HIV/AIDS flag, HIV/AIDS cause of death, record of KS, or definitive mention of HIV/AIDS from registry abstracts or death certificates. However, as outlined above, our recommendations for classifying HIV-associated NHL, HL, and anal cancer differed by cancer site.
The accuracy of an HIV/AIDS classification system based on cancer registry and death information ultimately depends on the validity of the medical records and death certificates from which this information is derived. The few studies addressing the quality of these sources of information suggest acceptable sensitivity. Cancer registry abstracts were found to mention HIV in 82% of San Francisco NHL patients known to be HIV positive through recruitment for a case-control study, 21 and death certificates recorded HIV infection or AIDS for 91% of deceased AIDS patients in a San Francisco HIV cohort study. 22 Thus, our method, particularly the classification of persons with only 1 source or indicator of HIV-positive status, remains susceptible to misclassification, particularly false classification of truly HIV-positive persons as HIV negative.
Our results indicate that linkage with the AIDS registry identified substantially fewer HIV/AIDS-associated cancer patients than could be detected with cancer registry–available information, even among those with AIDS-defining conditions (NHL, KS), or death-certificate indication of AIDS. It is uncertain what proportion of HL and anal cancer patients did not link with the AIDS registry because the patient had not developed AIDS. in addition, although the linkage protocol included manual review of all possible matches, differences in patient-identifying information between the AIDS and cancer registries or faulty linkage methods could explain some or all of the discrepancy for NHL and KS patients. However, because study patients with evidence of AIDS who did not match with the AIDS registry were substantially more likely than matched patients to be female, over age 55, or alive at the study end date, but were equally likely to have been diagnosed in recent years or in San Francisco county, their failure to match may relate more to AIDS registry incompleteness. Such incompleteness could involve the entire patient record, as may occur when patients migrate interstate between initial AIDS registration and later cancer diagnosis, or be limited to patient identifiers (e.g, name, social security number, address) that would preclude confirmation of a possible match with cancer registry identifiers.
Few reports have addressed why AIDS and cancer registry records might not match appropriately. Grulich et al. 23 found that 86% of Australian HIV-associated NHL patients first identified as such as part of a case-control study later matched with the AIDS registry and that no false-positive matches occurred. In a Southern California population, Diamond et al. 24 reported that several NHL patients who did not match with the local AIDS registry had an HIV/AIDS underlying cause of death, consistent with our observation of non-linkage for persons with positive death evidence, and suggesting that linkage identified a maximum of 88% of true HIV-associated NHL patients. Our observation that only 75% of presumed HIV-associated NHL patients linked with the state AIDS registry may not necessarily bear on the results of AIDS-cancer registry matches conducted elsewhere. However, our results do underscore the possibility of linkage inadequacy and suggest that future AIDS-cancer registry matches should confirm the absence of cancer registry–available indicators of positive status in unmatched cases to ensure complete ascertainment among dually registered patients.
The generalizability of our results to other cancer registries should be explored further. Our methodology should be reasonable for use by other SEER registries or by any other US or international cancer registries with similar data resources and medical record abstraction protocols and without confidentiality restrictions on recording the HIV/AIDS status of cancer patients. On the other hand, the generalizability of our methodology may be impacted by certain features of the Greater San Francisco Bay Area population, which differs from others in its extremely high HIV prevalence (approximately 3.5% of the San Francisco County population in 2001) 25 and the predominance of gay and bisexual men in its HIV-infected population. Thus, availability of HIV information in medical or cancer registry records may be different in this than in other regions. For example, as KS is more common in gay and bisexual men, owing to sexual transmission of the presumed etiologic virus, 26 it may have lower prevalence in populations with lower proportions of this HIV risk group. Similarly, the higher prevalence of HIV disease in San Francisco might correspond with improved medical surveillance and disease reporting than in low-incidence areas.
The introduction of HAART has intensified the need for timely population-based surveillance of cancer in HIV-infected persons, but, paradoxically, it has also made it more methodologically complex. Because HAART slows progression from HIV infection to the development of AIDS and from AIDS to death, 27,28 fewer HIV-infected persons will be identifiable as such on the basis of AIDS registry linkages and death records. Thus, going forward, our methodology for identifying HIV-associated cancers in cancer registry data likely will be based on higher proportions of patients identified by only 1 source of evidence. Indeed, the proportions of NHL, HL, and anal cancer patients identified by a single source were higher in 1996–998 (33, 68, and 71%, respectively) after the introduction of HAART, than in 1990–1995 (13, 36, and 37%, respectively). Furthermore, availability of HIV indicators may differ by factors influencing access to HAART. In San Francisco County, African-Americans, injection drug users, and persons without health insurance were less likely to have used HAART before AIDS diagnosis. 29 As demonstrated in these data, there is a need for all future activities for the surveillance of HIV-associated cancers, including AIDS-cancer registry matches, to incorporate as many diverse sources of information as possible to optimize detection and accurate classification of cases.
In the Greater San Francisco Bay Area, population-based cancer registry surveillance of HIV-associated cancers identified using registry-available data offers reasonable completeness and involves less administrative challenge and, thus, the opportunity for improved timeliness, compared with surveillance limited to AIDS registry-linked data. Using the methodologies outlined here, some measures of the burden of HIV-associated cancer, such as case counts, patient characteristics, and survival time, are readily calculated, while others, specifically cancer rates, are more difficult to estimate, due to challenges in estimating the underlying population at risk. While AIDS registry linkage-based studies circumvent this issue by using all AIDS-registry patients as the population at risk, analyses of cancer registry data can estimate the burden of HIV-associated cancers as the difference between overall rates and rates in presumed HIV-negative persons based on census-based population denominators. 30 However, improved methods are needed for estimating age-, sex-, and race-specific numbers of HIV-infected persons at risk. Production of these estimates may be facilitated with the advent of HIV surveillance programs, initiated recently in California. Even as we await such methodologic refinements, cancer registry data should be investigated more fully in more regions as an important resource for the population-based surveillance of HIV-associated cancer, especially in light of HAART-related reductions in AIDS registrations.
The authors thank Dr. Scarlett Lin Gomez, Patricia Harasty, Anne-Marie France, and Mary Schroeder for their contributions to this study; Marie Jungkeit, Jim Creeger, and Dr. Juan Ruiz of the California Department of Health Services Office of AIDS for conducting the data linkage; and Julie Durr, Dr. Maryjean Schenk, and Dr. Rick Severson of the Karmanos Cancer Institute, Detroit, MI, for their collaboration on development of the criteria for presumptive evidence.
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