The AHS is a prospective cohort study of 52,394 licensed private pesticide applicators in Iowa (IA) and North Carolina (NC), 32,346 spouses of these private applicators, and 4,916 licensed commercial applicators from IA. A detailed description of this cohort has been described.(14 (link)) Briefly, applicators were recruited at pesticide licensing stations from December 1993 through December 1997. Private applicators are generally farmers or nursery workers, and commercial applicators are persons employed by pest control companies or businesses that use pesticide applications, such as grain elevators. At enrollment, applicators completed a self-administered questionnaire that provided detailed information on various agricultural exposures, basic demographics, and lifestyle information. Spouses provided such information though a mailed questionnaire sent home with applicators.
We calculated SIRs to compare the cancer experience of licensed private pesticide applicators and their spouses in IA and NC to the general populations in those states. Commercial applicators were only recruited from Iowa and incidence rates were compared to those for the general population of that state. Cohort members were linked to cancer registry files for case identification and to the state death registries and to the National Death Index to ascertain vital status. AHS data release P1REL0712.01 was used, which includes observed numbers of cases for each cancer site that were accrued from the time of enrollment into the AHS (1993–1997) through December 31, 2006; cancer cases identified by the cancer registries as having occurred prior to enrollment were not included. Person-year accumulation began on the date of enrollment in the study and ended on December 31 2006, the last date known alive, the date of cancer diagnosis, or the date the study participant left the state of IA or NC, whichever came first. Cohort members were matched annually to current address records of the Internal Revenue Service, motor vehicle registration offices, and pesticide license registries of state agricultural departments to identify whether the participants continued to reside in Iowa or North Carolina. Less than 1% of the cohort moved out of state (N=390). Expected numbers of cases were calculated by applying 5-year age, calendar year, race and gender-specific incidence rates from IA or NC to the person-year distribution of the cohort using SEER*Stat Version 6.6.1 (http://seer.cancer.gov/seerstat/ ). Statistical significance of the SIRs was calculated based on Poisson 95% confidence intervals (CIs) as described by Breslow and Day.(15 ) SIRs were reported when there were at least 5 observed cases. Stratified SIRs by smoking status (never, former, current smoker) and state/subject type (private applicators from IA, private applicators from NC, IA spouses, and NC spouses) were also evaluated. Expanded subgroups for non-Hodgkin lymphoma (NHL) were presented to account for the known etiologic heterogeneity among various subtypes.(16 (link)) These subgroups include B-cell subtypes, diffuse large B-cell lymphoma (DLBCL), follicular lymphoma (FL), chronic lymphocytic leukemia/small lymphocytic lymphoma/mantle cell lymphoma (CLL/SLL/MCL), marginal zone lymphoma (MZL), and all T-cell subtypes combined.
Our previous analysis revealed a deficit for all cancers in AHS farmers and spouses.(13 (link)) Consequently, a test of the null hypothesis of one for a cause-specific SIR fails to account for this overall cancer deficit. Therefore, we also evaluated whether there was an excess or deficit of cancer cases for each specific cause relative to the overall deficit of cancers in AHS subjects. To do this, we calculated the ratio of the SIR for each site to the SIR for all cancer sites overall minus that site of interest [i.e., sitex vs. sitenot x]. This approach is related to the comparison of SMRs for exposed and unexposed groups as described in Breslow and Day.(15 ) These relative standardized incidence ratio (RSIR) and 95% CIs are presented for private applicators and spouses. Interpretability of the RSIR is predicated on the assumption that those factors responsible for the observed deficit for all cancers apply across the individual cancer sites in the absence of applicator-related factors.
We calculated SIRs to compare the cancer experience of licensed private pesticide applicators and their spouses in IA and NC to the general populations in those states. Commercial applicators were only recruited from Iowa and incidence rates were compared to those for the general population of that state. Cohort members were linked to cancer registry files for case identification and to the state death registries and to the National Death Index to ascertain vital status. AHS data release P1REL0712.01 was used, which includes observed numbers of cases for each cancer site that were accrued from the time of enrollment into the AHS (1993–1997) through December 31, 2006; cancer cases identified by the cancer registries as having occurred prior to enrollment were not included. Person-year accumulation began on the date of enrollment in the study and ended on December 31 2006, the last date known alive, the date of cancer diagnosis, or the date the study participant left the state of IA or NC, whichever came first. Cohort members were matched annually to current address records of the Internal Revenue Service, motor vehicle registration offices, and pesticide license registries of state agricultural departments to identify whether the participants continued to reside in Iowa or North Carolina. Less than 1% of the cohort moved out of state (N=390). Expected numbers of cases were calculated by applying 5-year age, calendar year, race and gender-specific incidence rates from IA or NC to the person-year distribution of the cohort using SEER*Stat Version 6.6.1 (
Our previous analysis revealed a deficit for all cancers in AHS farmers and spouses.(13 (link)) Consequently, a test of the null hypothesis of one for a cause-specific SIR fails to account for this overall cancer deficit. Therefore, we also evaluated whether there was an excess or deficit of cancer cases for each specific cause relative to the overall deficit of cancers in AHS subjects. To do this, we calculated the ratio of the SIR for each site to the SIR for all cancer sites overall minus that site of interest [i.e., sitex vs. sitenot x]. This approach is related to the comparison of SMRs for exposed and unexposed groups as described in Breslow and Day.(15 ) These relative standardized incidence ratio (RSIR) and 95% CIs are presented for private applicators and spouses. Interpretability of the RSIR is predicated on the assumption that those factors responsible for the observed deficit for all cancers apply across the individual cancer sites in the absence of applicator-related factors.
