Assessing uncertainty in reference intervals via tolerance intervals: application to a mixed model describing HIV infection

We define the reference interval as the range between the 2.5th and 97.5th percentiles of a random variable. We use reference intervals to compare characteristics of a marker of disease progression between affected populations. We use a tolerance interval to assess uncertainty in the reference interval. Unlike the tolerance interval, the estimated reference interval does not contains the true reference interval with specified confidence (or credibility). The tolerance interval is easy to understand, communicate and visualize. We derive estimates of the reference interval and its tolerance interval for markers defined by features of a linear mixed model. Examples considered are reference intervals for time trends in HIV viral load, and CD4 per cent, in HIV-infected haemophiliac children and homosexual men. We estimate the intervals with likelihood methods and also develop a Bayesian model in which the parameters are estimated via Markov-chain Monte Carlo. The Bayesian formulation naturally overcomes some important limitations of the likelihood model.

Serologic Evidence for Exposure to Simian Virus 40 in North American Zoo Workers

Some laboratories have detected DNA from the macaque polyomavirus simian virus 40 (SV40) in human tumors, but possible routes of infection remain unknown. In the present study, an enzyme immunoassay using viruslike particles (VLPs) was used to test 254 zoo workers for antibodies to SV40; 25 zoo workers with direct contact with nonhuman primates and 15 other zoo workers (23% vs. 10%, respectively; P=.01) were seropositive for SV40. Additionally, SV40 seroreactivity confirmed by competitive-inhibition experiments (i.e., blocked by addition of SV40 VLPs but not by VLPs for BK virus or JC virus, which are related human polyomaviruses) was increased in zoo workers with direct contact with nonhuman primates (10% vs. 3%, respectively; P=.04). SV40 seroreactivity therefore may reflect zoonotic exposure.

The Incidence of Kaposi Sarcoma Among Injection Drug Users With AIDS in the United States

Some studies report increased prevalence of human herpesvirus 8 (HHV-8), the causative agent of Kaposi sarcoma (KS), among injection drug users (IDUs), suggesting that HHV-8 may be transmitted through blood-borne or other exposures common in this population. Since an elevated HHV-8 prevalence in IDUs would likely lead to increased KS incidence, KS incidence was studied in IDUs and non-IDU's with AIDS. AIDS-related KS cases were identified using linked US AIDS and cancer registry data for 25,891 women, 47,782 heterosexual men, and 90,616 men who have sex with men (MSM). KS arose in 7099 persons with AIDS. KS incidence was highest for MSM (5.7 per 100 person-years), substantially lower for heterosexual men (0.7 per 100 person-years), and lowest for women (0.4 per 100 person-years). After adjustment for age, race, registry location, and year of AIDS onset, relative risks for KS associated with injection drug use were 1.3 (95% CI, 0.9-1.8) among women, 1.1 (0.7-1.6) among heterosexual men, and 0.9 (0.8-0.9) among MSM. It is concluded that injection drug use was not associated with an increased risk of AIDS-related KS. Thus, these data suggest that IDUs' risk of acquiring HHV-8, through needle sharing or other behaviors related to injection drug use, is low.

Case-Control Study of Simian Virus 40 and Non-Hodgkin Lymphoma in the United States

BACKGROUND

Recent studies have reported detection of simian virus 40 (SV40) DNA in tumor tissues from 15%-43% of U.S. non-Hodgkin lymphoma (NHL) patients. SV40 accidentally contaminated U.S. poliovirus vaccines that were widely administered from 1955 through 1962. However, epidemiologic data linking SV40 with NHL are lacking.

METHODS

We obtained serum samples from 724 incident NHL case patients and 622 control subjects from a population-based U.S. case-control study. SV40 serostatus was analyzed by two independent laboratories (designated A and B) using similar virus-like particle (VLP) enzyme immunoassays. Associations with serostatus were assessed with logistic regression, adjusting for sex, race, birth year, and study site. VLPs for the human polyomaviruses BK and JC were used in competitive inhibition experiments to assess the specificity of SV40 reactivity. Statistical tests were two-sided.

RESULTS

SV40 antibody results from the two laboratories were correlated (R = 0.59; P<.001). Laboratories A and B detected SV40 seropositivity in 7.2% and 9.8% of NHL case patients, respectively, and in 10.5% and 9.6% of control subjects, respectively. SV40 seropositivity was not associated with increased NHL risk (laboratory A: adjusted odds ratio [OR] = 0.68, 95% confidence interval [CI] = 0.46 to 1.00; laboratory B: adjusted OR = 1.02, 95% CI = 0.71 to 1.47). SV40 seropositivity was not associated with NHLs of any specific histology or site. Among subjects born before 1963, 1.0%-1.6% showed SV40-specific reactivity, i.e., SV40 reactivity confirmed in competitive inhibition experiments, whereas (based on limited data) none born subsequently demonstrated SV40-specific reactivity.

CONCLUSIONS

In persons born before 1963, the presence of SV40-specific antibodies, although rare, could reflect exposure to SV40-contaminated vaccines. Nevertheless, NHL risk was unrelated to serologic evidence of SV40 exposure or infection.

Detection of kaposi sarcoma-associated herpesvirus DNA in saliva and buffy-coat samples from children with sickle cell disease in Uganda

Among 233 children, Kaposi sarcoma-associated herpesvirus (KSHV) DNA was detected in 43% of children seropositive for both K8.1 and orf73, in 29% of children seropositive for K8.1 only, in 14% of children seropositive for orf73 only, and in 7% of children seronegative for both K8.1 and orf73; among 228 mothers, KSHV DNA was detected in 27%, 25%, 4%, and 1%, respectively. KSHV DNA was detected more frequently and at higher levels in saliva than in buffy-coat samples and in children than in mothers. In both children and mothers, detection in saliva was associated with detection in peripheral blood. Detection was associated with K8.1 seropositivity, younger age, and high household density, indicating the importance of in-household person-to-person transmission, likely via saliva.

Poliovirus vaccination during pregnancy, maternal seroconversion to simian virus 40, and risk of childhood cancer

Before 1963, poliovirus vaccine produced in the United States was contaminated with simian virus 40 (SV40), which causes cancer in animals. To examine whether early-life SV40 infection can cause human cancer, the authors studied 54,796 children enrolled in the US-based Collaborative Perinatal Project (CPP) in 1959-1966, 52 of whom developed cancer by their eighth birthday. Those children whose mothers had received pre-1963 poliovirus vaccine during pregnancy (22.5% of the children) had an increased incidence of neural tumors (hazard ratio = 2.6, 95% confidence interval: 1.0, 6.7; 18 cases) and hematologic malignancies (hazard ratio = 2.8, 95% confidence interval: 1.2, 6.4; 22 cases). For 50 CPP children with cancer and 200 CPP control children, the authors tested paired maternal serum samples from pregnancy for SV40 antibodies using a virus-like particle enzyme immunoassay and a plaque neutralization assay. Overall, mothers exhibited infrequent, low-level SV40 antibody reactivity, and only six case mothers seroconverted by either assay. Using the two SV40 assays, maternal SV40 seroconversion during pregnancy was not consistently related to children's case/control status or mothers' receipt of pre-1963 vaccine. The authors conclude that an increased cancer risk in CPP children whose mothers received pre-1963 poliovirus vaccine was unlikely to have been due to SV40 infection transmitted from mothers to their children.

Case-control study of cancer among US Army veterans exposed to simian virus 40-contaminated adenovirus vaccine

Simian virus 40 (SV40) was an accidental contaminant of vaccines produced in monkey kidney tissue cultures in the 1950s and early 1960s, including a parenteral adenovirus vaccine given to several hundred thousand US military recruits. Detection of SV40 DNA in tumor tissues by some laboratories suggests that SV40 contributes to human cancers. To determine if entry into US Army service during periods of administration of SV40-contaminated adenovirus vaccine was associated with an increased risk of cancer, the authors conducted a case-control study of cancer occurring in male Army veterans who entered service in 1959-1961. Cases of brain tumors (n = 181), mesothelioma (n = 10), and non-Hodgkin's lymphoma (n = 220) were identified through a Veterans Administration hospital discharge database, as were colon cancer and lung cancer controls (n = 221). Exposure to adenovirus vaccine was assigned on the basis of known periods of adenovirus vaccine administration and dates of Army entry obtained for cancer cases and controls. The odds ratios associated with exposure to SV40-contaminated adenovirus vaccine were 0.81 (95% confidence interval (CI): 0.52, 1.24) for brain tumors, 1.41 (95% CI: 0.39, 5.15) for mesothelioma, and 0.97 (95% CI: 0.65, 1.44) for non-Hodgkin's lymphoma. These findings do not support a role for SV40 in the development of these cancers.

Hepatitis C virus infection and non-Hodgkin lymphoma: results of the NCI-SEER multi-center case-control study

Several studies have noted elevated hepatitis C virus (HCV) prevalence among patients with non-Hodgkin lymphoma (NHL), suggesting that HCV infection increases NHL risk through chronic immune stimulation. Population-based data from the U.S. are lacking. In a population-based case-control study of NHL in the United States, we identified HCV infection using an enzyme immunoassay, confirmed by recombinant immunoblot assay or HCV RNA detection. The association between HCV and NHL was assessed using logistic regression, adjusting for demographic factors, illicit drug use or medical history. Thirty-two of 813 (3.9%) NHL cases and 14 of 684 (2.1%) controls were HCV-infected [odds ratio (OR) 1.96, 95%CI 1.07-4.03]. For separate NHL subtypes, numbers were limited. Nonetheless, positive associations were noted for follicular (OR 2.46, 95%CI 1.01-5.81), marginal zone (3.99, 0-13.6) and mucosa-associated lymphoid tissue (2.04, 0-7.20) NHLs. For all NHLs combined, the HCV-NHL association changed little after adjustment for sex, age, race and study center (OR 1.89, 95%CI 1.00-4.00). HCV was common in controls who had injected drugs (40%) or used other illicit drugs (6.5%), but adjustment for drug use did not affect the HCV-NHL association (OR 1.87, 95%CI 0.95-4.10). Transfusion history was unrelated to HCV status, and adjustment for this exposure did not attenuate the HCV-NHL association (OR 2.15, 95%CI 1.12-4.76). Excluding 4 subjects with a history of hemodialysis or 3 subjects with organ transplants also did not affect the results. Our study demonstrates an association between HCV infection and NHL in the United States. HCV infection may be a cause of NHL.

Absence of human T-cell lymphotropic virus type I and human foamy virus in thymoma

The cause of thymoma, a rare malignancy of thymic epithelial cells, is unknown. Recent studies have reported the detection of DNA from human T-cell lymphotropic virus type I (HTLV-I) and human foamy virus (HFV) in small numbers of thymoma tumours, suggesting an aetiologic role for these retroviruses. In the present study, we evaluated 21 US thymoma patients and 20 patients with other cancers for evidence of infection with these viruses. We used the polymerase chain reaction to attempt to amplify viral DNA from tumour tissues, using primers from the pol and tax (HTLV-I) and gag and bel1 (HFV) regions. In these experiments, we did not detect HTLV-I or HFV DNA sequences in any thymoma or control tissues, despite adequate sensitivity of our assays (one HTLV-I copy per 25 000 cells, one HFV copy per 7500 cells). Additionally, none of 14 thymoma patients evaluated serologically for HTLV I/II infection was positive by enzyme-linked immunoassay (ELISA), while five (36%) had indeterminate Western blot reactivity. In comparison, one of 20 US blood donors was HTLV-I/II ELISA positive, and nine (45%) donors, including the ELISA-positive donor, had indeterminate Western blot reactivity. Western blot patterns varied across individuals and consisted mostly of weak reactivity. In conclusion, we did not find evidence for the presence of HTLV-I or HFV in US thymoma patients.

Hepatitis C virus and risk of non-Hodgkin lymphoma: a population-based case-control study among Connecticut women

OBJECTIVES

Previous epidemiologic studies of hepatitis C virus (HCV) infection and B-cell non-Hodgkin lymphoma (B-NHL) have yielded conflicting results, perhaps due to differences in the classification of B-NHL and the choice of non-population-based control groups that may not reflect the background population prevalence of HCV. To further investigate the link between HCV and NHL, we conducted HCV testing on serum samples of 998 women (464 cases; 534 controls) from a population-based case-control study of women in Connecticut.

METHODS

Serum samples were screened for HCV antibodies using an enzyme immunoassay; positive samples were confirmed by additional testing for HCV antibodies and for serum HCV RNA.

RESULTS

Approximately 2% (8 of 464) of cases and 1% (5 of 534) of controls tested positive for HCV. The risk of NHL associated with HCV infection appeared to be concentrated among B-cell lymphomas [odds ratio (OR) 2.0; 95% confidence interval (CI) 0.6, 8.2], particularly among follicular lymphomas (OR 4.1, 95% CI 0.8, 19.4).

CONCLUSIONS

The primary strength of this study is our use of a population-based study design, although the low prevalence of HCV among women in Connecticut resulted in wide CIs for the estimated association between HCV and B-NHL subtypes. Our study suggests that HCV may be associated with increased risk of development of B-NHL, and that this risk may vary by B-NHL subtype among women. Due to the relatively low prevalence of HCV in our study population and the scarcity of population-based epidemiological research on this subject, our study highlights the need for additional large, population-based studies of the role of HCV in the etiology of B-NHL.

Hepatitis C Virus and Risk of Non-Hodgkin Lymphoma: A Population-Based Case-Control Study among Connecticut Women

Objective: Previous epidemiologic studies of hepatitis C virus (HCV) infection and B-cell non-Hodgkin lymphoma (B-NHL) have yielded conflicting results, perhaps due to differences in the classification of B-NHL and the choice of non-population-based control groups that may not reflect the background population prevalence of HCV. To further investigate the link between HCV and NHL, we conducted HCV testing on serum samples of 998 women (464 cases; 534 controls) from a population-based case-control study of women in Connecticut. Methods: Serum samples were screened for HCV antibodies using an enzyme immunoassay; positive samples were confirmed by additional testing for HCV antibodies and for serum HCV RNA. Results: Approximately 2% (8 of 464) of cases and 1% (5 of 534) of controls tested positive for HCV. The risk of NHL associated with HCV infection appeared to be concentrated among B-cell lymphomas [odds ratio (OR) 2.0; 95% confidence interval (CI) 0.6, 8.2], particularly among follicular lymphomas (OR 4.1, 95% CI 0.8, 19.4). Conclusion: The primary strength of this study is our use of a population-based study design, although the low prevalence of HCV among women in Connecticut resulted in wide CIs for the estimated association between HCV and B-NHL subtypes. Our study suggests that HCV may be associated with increased risk of development of B-NHL, and that this risk may vary by B-NHL subtype among women. Due to the relatively low prevalence of HCV in our study population and the scarcity of population-based epidemiological research on this subject, our study highlights the need for additional large, population-based studies of the role of HCV in the etiology of B-NHL.

Birth weight as a risk factor for childhood leukemia: a meta-analysis of 18 epidemiologic studies

Evidence has emerged that childhood leukemia is initiated in utero. High birth weight is one of the few birth-related factors that has been associated with childhood leukemia, albeit not consistently. The authors conducted a meta-analysis of studies of the association between birth weight and childhood leukemia risk. Study-specific odds ratios for leukemia were calculated, using a cutoff at 4,000 g of birth weight. The authors also evaluated whether the association between birth weight and leukemia followed a log-linear dose-response-like pattern. They calculated summary estimates using weighted averages of study-specific odds ratios from dichotomous and trend analyses. Eighteen studies (published between 1962 and 2002) were included, encompassing 10,282 children with leukemia. Children weighing 4,000 g or more at birth were at higher risk of acute lymphoblastic leukemia than children weighing less (odds ratio (OR) = 1.26, 95% confidence interval (CI): 1.17, 1.37). Furthermore, data were consistent with a dose-response-like effect (OR = 1.14/1,000-g birth weight increase, 95% CI: 1.08, 1.20). Studies of acute myeloid leukemia indicated a similar increase in risk for children weighing 4,000 g or more at birth (OR = 1.27, 95% CI: 0.73, 2.20) and a dose-response-like effect (OR = 1.29/1,000 g, 95% CI: 0.80, 2.06), but results varied across studies. Our findings support a relation between birth weight and childhood acute lymphoblastic leukemia risk and emphasize the need for additional studies of the biologic mechanisms underlying this association.

Human herpesvirus 8 infection and transfusion history in children with sickle-cell disease in Uganda

BACKGROUND

Although human herpesvirus 8 (HHV-8), the etiologic agent for Kaposi's sarcoma, can be detected in peripheral blood, blood-borne transmission of this virus has not been demonstrated. We studied the association between HHV-8 seropositivity and transfusion history among children with sickle-cell disease in Uganda, where HHV-8 infection is common in blood donors.

METHODS

We studied 600 children (aged 0-16 years) with sickle-cell disease at Mulago Hospital, Kampala, from November 2001 through April 2002. By design, about half had previously been transfused. HHV-8 serostatus was determined using enzyme-linked immunosorbent assays for antibodies against HHV-8 proteins K8.1 and orf 73. We used logistic regression to test for an association between HHV-8 serostatus and transfusion history and a Markov model to estimate the transmission risk per transfusion and the cumulative risk from community (i.e., nontransfusion) sources. Statistical tests were two-sided.

RESULTS

HHV-8 antibodies were detected in 117 of 561 (21%) children with unambiguous K8.1 results. HHV-8 seroprevalence among the never-transfused children increased with age from 7% in children aged 0-2 years to 32% in those aged 13-16 years (P(trend)<.001). HHV-8 seropositivity was more frequent in transfused than never-transfused children (24% versus 17%, odds ratio = 1.48, 95% confidence interval [CI] = 0.97 to 2.26; P =.07). Seropositivity increased with number of reported transfusions, with age-adjusted odds ratios of 0.97 (95% CI = 0.54 to 1.75), 1.13 (95% CI = 0.59 to 2.17), 1.76 (95% CI = 0.81 to 3.83), and 2.17 (95% CI = 1.18 to 3.99) for children with one, two, three, or four or more transfusions, respectively (P(trend) =.007). Overall, the estimated HHV-8 transmission risk was 2.6% per transfusion (95% CI = 1.9% to 3.3%), whereas the annual risk of infection unrelated to transfusion was 2.7% (95% CI = 1.7% to 3.7%).

CONCLUSION

Our study suggests that blood transfusion is associated with a small risk of HHV-8 transmission. In Uganda, this risk is approximately equivalent to the 1-year cumulative risk of infection from community sources.

Multicenter comparison of serologic assays and estimation of human herpesvirus 8 seroprevalence among US blood donors

BACKGROUND

As part of assessing the possibility of transfusion transmission of human herpesvirus 8 (HHV-8 or Kaposi's sarcoma-associated herpesvirus), HHV-8 seroprevalence was estimated among US blood donors, the performance of HHV-8 serologic tests was compared, and the presence of HHV-8 DNA was tested for in donated blood.

STUDY DESIGN AND METHODS

Replicate panels of 1040 plasma specimens prepared from 1000 US blood donors (collected in 1994 and 1995) and 21 Kaposi's sarcoma patients were tested for antibodies to HHV-8 in six laboratories. HHV-8 PCR was performed on blood samples from 138 donors, including all 33 who tested seropositive in at least two laboratories and 22 who tested positive in at least one.

RESULTS

The estimated HHV-8 seroprevalence among US blood donors was 3.5 percent (95% CI, 1.2%-9.8%) by a conditional dependence latent-class model, 3.0 percent (95% CI, 2.0%-4.6%) by a conditional independence latent-class model, and 3.3 percent (95% CI, 2.3%-4.6%) by use of a consensus-derived gold standard (specimens positive in two or more laboratories); the conditional dependence model best fit the data. In this model, laboratory specificities ranged from 96.6 to 100 percent. Sensitivities ranged widely, but with overlapping 95 percent CIs. HHV-8 DNA was detected in blood from none of 138 donors evaluated.

CONCLUSIONS

Medical and behavioral screening does not eliminate HHV-8-seropositive persons from the US blood donor pool, but no viral DNA was found in donor blood. Further studies of much larger numbers of seropositive individuals will be required to more completely assess the rate of viremia and possibility of HHV-8 transfusion transmission. Current data do not indicate a need to screen US blood donors for HHV-8.

Childhood exposure to simian virus 40-contaminated poliovirus vaccine and risk of AIDS-associated non-Hodgkin's lymphoma

Persons with acquired immunodeficiency syndrome (AIDS) have increased risk for non-Hodgkin's lymphoma (NHL). Recent studies have reported the detection of DNA sequences from simian virus 40 (SV40), a macaque polyomavirus that contaminated early poliovirus vaccines, in a large proportion of AIDS-associated NHLs. To examine the association between SV40 exposure and NHL risk, we analyzed data from a U.S. registry-based cohort study of persons with AIDS (1980-96). We calculated NHL incidence in persons born in 1958-61 (exposed to SV40-contaminated poliovirus vaccine as children, n = 39,468) and in 1964-67 (born after vaccines were cleared of SV40 and thus unexposed, n = 17,340). Among persons with AIDS, NHL incidence was 11.7 per 1,000 person-years in SV40-exposed individuals (616 NHL cases) and 10.1 per 1,000 person-years in SV40-unexposed individuals (230 cases; unadjusted relative risk 1.15, 95% CI 0.99-1.34, p = 0.06). Because of differences in cohorts' birth years and the evolving demographics of the AIDS epidemic, SV40-exposed subjects were older at AIDS onset than unexposed subjects (mean age 32.0 vs. 27.2 years, p < 0.0001), and the cohorts differed by sex (p < 0.0001) and ethnic group (p < 0.0001). Since NHL incidence was relatively high among whites (p < 0.0001) and homosexual males (p < 0.0001) and increased with age (p = 0.09), comparisons required adjustments for these factors. After adjustment, SV40 exposure was not associated with NHL incidence (adjusted relative risk 0.97, 95% CI 0.79-1.20, p = 0.80). We conclude that childhood exposure to SV40 through receipt of contaminated poliovirus vaccine was not associated with increased risk for AIDS-associated NHL. Our findings do not support a role for SV40 in lymphomagenesis among immunosuppressed persons.

Detection and quantification of Kaposi's sarcoma-associated herpesvirus to predict AIDS-associated Kaposi's sarcoma

OBJECTIVE

To identify immunologic and virologic predictors of AIDS-associated Kaposi's sarcoma (KS).

DESIGN

Nested case-control analysis of KS risk in a cohort of 132 HIV-infected homosexual men in New York and Washington, DC, USA.

METHODS

For each KS case, we selected two HIV-infected controls, matched for CD4 cell count and Kaposi's sarcoma-associated herpesvirus (human herpesvirus 8; KSHV) serostatus (enzyme immunoassay for antibody to KSHV protein K8.1). Cell-associated KSHV and Epstein-Barr virus (EBV) viral loads were measured with quantitative real-time PCR assays on samples collected 1 year (median) before KS diagnosis.

RESULTS

Thirty-one men developed AIDS-associated KS (incidence 3.1 per 100 person years). Among HIV-infected men, KS incidence was higher among those with K8.1 seropositivity (5.0 versus 1.4 per 100 person years; P = 0.004), low CD4 cell count [hazard ratio (HR), 1.49; 95% confidence interval (CI), 1.24-1.79 per 100 x 10(6) cells/l decline), or high HIV RNA level (HR, 3.96; 95% CI, 2.19-7.16 per log(10)). In the case-control analysis, nine of 70 evaluated subjects had KSHV viremia, generally low level (median viral load 180 copies per 1 x 10(6) cells). KSHV viremia was associated with increased KS risk (unadjusted odds ratio, 9.1; 95% CI, 1.7-48; odds ratio, 11.7; 95% CI, 1.8-76 after adjustment for K8.1 serostatus, CD4 cell count, and HIV RNA). Among K8.1-seropositive subjects, KS incidence was tenfold higher in those with KSHV viremia (30.3 per 100 person years versus 3.4 per 100 person years in those without viremia). Also, EBV viral loads were higher in cases than in controls (P = 0.07).

CONCLUSIONS

Among individuals with HIV-KSHV coinfection, KSHV viremia identifies a subgroup with extremely high risk for developing KS.

Malignant thymoma in the United States: demographic patterns in incidence and associations with subsequent malignancies

The cause of thymoma is unknown. No population-based study has described demographic patterns of thymoma incidence. Previous reports have linked thymoma with diverse subsequent malignancies, but these associations are uncertain. We used Surveillance, Epidemiology and End Results (SEER) data to study the incidence of malignant thymoma by sex, age and race in the United States (1973-1998). Incidence was modeled with joinpoint regression (for age) and Poisson regression. We also used SEER data to compare malignancies following thymoma diagnosis with those expected from general population rates, calculating the standardized incidence ratio (SIR, observed/expected cases) to measure risk. The overall incidence of malignant thymoma was 0.15 per 100000 person-years (849 cases). Thymoma incidence increased into the 8th decade of age and then decreased. Incidence was higher in males than females (p=0.007) and was highest among Asians/Pacific Islanders (0.49 per 100000 person-years). Following thymoma, there were 66 malignancies (SIR 1.5, 95%CI 1.2-1.9). The most notable excess risk for subsequent malignancy was for non-Hodgkin's lymphoma (B immunophenotype) where the SIR was 4.7 (95%CI 1.9-9.6, 7 cases). There were also excess digestive system cancers (SIR 1.8, 95%CI 1.1-2.9) and soft tissue sarcomas (SIR 11.1, 1.3-40.1). No other cancers were increased after thymoma. In conclusion, malignant thymoma is extremely rare. The peak in late adulthood deserves further study. Variation in incidence by race suggests a role for genetic factors. Our study did not demonstrate broadly increased risk for malignancies following thymoma.

Immunoblastic lymphoma in persons with AIDS-associated Kaposi's sarcoma: a role for Kaposi's sarcoma-associated herpesvirus

Kaposi's sarcoma-associated herpesvirus, the viral agent of Kaposi's sarcoma, is associated with two lymphoproliferative disorders: primary effusion lymphoma and multicentric Castleman's disease. To identify other lymphoproliferative conditions linked with Kaposi's sarcoma-associated herpesvirus, we studied non-Hodgkin's lymphomas arising in individuals with AIDS-associated Kaposi's sarcoma. Formalin-fixed tissues from 24 such lymphomas were examined. As expected, two primary effusion lymphomas were Kaposi's sarcoma-associated herpesvirus-positive, with immunohistochemistry demonstrating the Kaposi's sarcoma-associated herpesvirus latency-associated nuclear antigen in the nuclei of all neoplastic cells. Additionally, three of seven evaluable cases of the immunoblastic variant of diffuse large B-cell lymphoma (immunoblastic lymphoma) showed similar latency-associated nuclear antigen staining. These Kaposi's sarcoma-associated herpesvirus-positive immunoblastic lymphomas resembled primary effusion lymphoma histologically but were not known to involve body cavities (sites included lymph nodes, soft tissues of the neck, and spleen). Notably, 5-20% of the neoplastic cells in the Kaposi's sarcoma-associated herpesvirus-positive immunoblastic lymphomas also showed cytoplasmic staining for viral interleukin-6, a biologically active cytokine homologue found in primary effusion lymphoma. We conclude that Kaposi's sarcoma-associated herpesvirus is present in some immunoblastic lymphomas in persons with AIDS-associated Kaposi's sarcoma.

Lack of serological evidence for an association between simian virus 40 and lymphoma

Recent studies have implicated simian virus 40 (SV40) in non-Hodgkin's lymphomas based on detection of SV40 DNA sequences. We employed a virus-like-particle (VLP)-based enzyme immunoassay for antibodies to SV40 to test sera from 520 lymphoma cases and 587 controls in Spain. The SV40 seroprevalence was 9.5% in controls and 5.9% in cases. Antibody levels of the positive sera were low. There was no association of SV40 seropositivity with any subtype of lymphoma. VLPs of the human BK virus substantially inhibited the SV40 reactivity of human sera. There was no serological evidence of widespread SV40 infection and no association of SV40 seropositivity with human lymphomas in Spain.

Immune deficiency and risk for malignancy among persons with AIDS

BACKGROUND

People with AIDS have an elevated risk for cancer. We studied the relationship between cancer risk and AIDS-related immunosuppression as measured by CD4 count at AIDS onset.

METHODS

We linked records from AIDS and cancer registries in 11 US regions (1990-1996). We studied 82,217 (86.6%) adults who had a CD4 count measured at AIDS onset and survived into the follow-up period. We calculated standardized incidence ratios (SIRs) for AIDS-defining (Kaposi sarcoma [KS], non-Hodgkin lymphoma [NHL] and cervical cancer) as well as non-AIDS-defining cancers in the 2 years after AIDS onset. For each cancer, the change in SIRs across CD4 counts (0-49 cells/mm3, 50-99 cells/mm3, 100-199 cells/mm3, and > or =200 cells/mm3) was modeled using Poisson regression.

RESULTS

The SIRs for KS, NHL, and cervical cancer were 258, 78, and 8.8, respectively. For each fall of 100 CD4 cells/mm3, RRs were 1.36 (95% CI: 1.29-1.43) for KS and 1.48 (95% CI: 1.37-1.59) for NHL. Among NHL subtypes, the association with lower CD4 counts was strongest for immunoblastic lymphoma (RR =1.64, 95% CI: 1.37-1.96, per decline of 100 CD4 cells/mm3) and central nervous system lymphoma (RR = 2.29, 95% CI: 1.95-2.69). The SIR for cervical cancer did not vary with CD4 count (p =.74). For non-AIDS-defining cancers (overall SIR = 2.1), neither the combined risk nor the risk of specific types was associated with declining CD4 counts.

CONCLUSION

SKS and NHL risk increased with level of immunosuppression at AIDS onset. Risks for other cancers, including cervical cancer, were unrelated to CD4 counts. Elevated risks for non-AIDS cancers may be a result of lifestyle factors.

Cancer incidence in Denmark following exposure to poliovirus vaccine contaminated with simian virus 40

BACKGROUND

Early poliovirus vaccines were accidentally contaminated with simian virus 40 (SV40). In Denmark, poliovirus vaccine was administered to most children from 1955 through 1961. SV40 DNA sequences have been detected in several human malignancies, including mesothelioma, ependymoma, choroid plexus tumors, and non-Hodgkin's lymphoma. To clarify whether SV40 infection increases risk of these cancers or of cancers arising in children, we examined cancer incidence in three Danish birth cohorts.

METHODS

Population-based cancer incidence data from 1943 through 1997 were obtained from the Danish Cancer Registry. The relationship between exposure to SV40-contaminated vaccine and cancer incidence was evaluated by examining incidence in birth cohorts that differed in exposure to SV40-contaminated vaccine. In addition, cancer incidence was examined in children who were 0-4 years of age before, during, and after the period of vaccine contamination. Incidence was compared using Poisson regression, adjusting for age differences. All statistical tests were two-sided.

RESULTS

After 69.5 million person-years of follow-up, individuals exposed to SV40-contaminated poliovirus vaccine as infants (i.e., born 1955-1961) or children (i.e., born 1946-1952) had lower overall cancer risk (age-adjusted relative risk [RR] = 0.86, 95% confidence interval [CI] = 0.81 to 0.91 and RR = 0.79, 95% CI = 0.75 to 0.84, respectively; P<.001 for both) than unexposed individuals (i.e., born 1964-1970, after the vaccine was cleared of SV40 contamination). Specifically, SV40 exposure was not associated with increased incidence of mesothelioma, ependymoma, choroid plexus tumor, or non-Hodgkin's lymphoma. After 19.5 million person-years of follow-up, incidence of all cancers combined, of intracranial tumors, and of leukemia among children aged 0-4 years was also not associated with SV40 exposure. Ependymoma incidence was higher during the exposed period than during the unexposed period (RR = 2.59, 95%CI = 1.36 to 4.92; P =.004 versus the period before contamination); however, incidence peaked in 1969, after the vaccine was cleared of SV40.

CONCLUSION

Exposure to SV40-contaminated poliovirus vaccine in Denmark was not associated with increased cancer incidence.

Seroprevalence of human herpesvirus 8 among injection drug users in San Francisco

The association between injection drug use and human herpesvirus 8 (HHV-8) was examined to investigate bloodborne transmission of the virus. In all, 1905 injection drug users (IDUs) enrolled in a cross-sectional study were tested for K8.1 antibodies to HHV-8 lytic antigen. Logistic regression was used to adjust for demographic and sexual behavior variables. HHV-8 seroprevalence was 10% among women, 10% among heterosexual men, and 23% among men who have sex with men. In adjusted analyses, HHV-8 seroprevalence increased with longer duration of injection drug use for each of these groups (P = .01, P = .03, and P = .049 for trend, respectively). HHV-8 infection is relatively common among IDUs in San Francisco, and longer duration of injection drug use is associated with an increase in the risk of HHV-8 infection that is not explained by sexual behavior or demographic differences. These results are consistent with the occurrence of bloodborne transmission of HHV-8 among IDUs.