(relative risk [RR]=2.7, 95% confidence interval [CI]=1.1–6.6). For a subset (n=10) exposed to organophosphate insecticides, there was an elevated but equivocal increase in risk (RR=1.9, 95% CI=0.6–5.9). The authors state that selection bias is improbable as an explanation for the associations because of the low refusal rate, but they do not discuss the limitation of hospital-based case-control studies in selecting control patients or the possibility of recall basis.
A companion study examined recent household insecticide use in the entire group of cases (n=253) and controls (n=1174) in Bangkok and in two rural regions of Thailand (Kaufman et al., 1997). Risk estimates were calculated for use of specific insecticides and for groups of insecticides, and multiple logistic regression analyses were used to control for confounding by concomitant use of more than one insecticide and for demographic variables. A moderate increase in risk was seen in the comparison of cases (n=32) and controls (n=117) that reported any exposure to an insecticide product that combined dichlorvos, propoxur, and cyfluthrin (a pyrethroid) (RR=1.7, 95% CI=1.1–2.8). However, for subsets of this exposure group, associations were increased but not statistically precise: regular use (RR=1.6, 95% CI=0.9–2.9) and application by the subject (RR=1.8, 95% CI =0.8–4.1). Evaluation of exposure to the classes of insecticides showed no trend with increasing exposure for the subsets that reported any exposure to carbamates (n=36) (RR=2.1, 95% CI=1.2–3.7), regular use of carbamates (n=19) (RR=2.0, 95% CI=1.0–4.1), or carbamates applied by the subject (n=11) (RR=2.3, 95% CI=0.8–6.5). No important increases were seen in the analyses that examined exposure to classes of insecticides (organophosphates, pyrethrins, or organochlorines). The authors acknowledge that the few positive associations could have occurred by chance in the course of conducting multiple comparisons.
A case-control study of cases identified from the French national aplastic-anemia registry used interviews with 98 patients, 181 hospitalized control subjects, and 72 neighbor control subjects (Guiguet et al., 1995). Detailed information was collected about occupational history, including tasks, exposures, environmental conditions, and protection. Risk of aplastic anemia was not consistently elevated for occupational exposure to insecticides (n=18) compared with hospitalized controls (odds ratio [OR]=1.6, 95% CI=0.8–3.0) or with neighbors (OR=0.4, 95% CI=0.1–1.3).
A case-control study in North Carolina evaluated the relationship between occupational pesticide exposure and fatal cases of aplastic anemia (Wang and Grufferman, 1981). Sixty deaths attributable to aplastic anemia were identified from state records; two controls that died in the same year were selected for each case. No relationship was found between deaths in cases with occupations that might have involved exposure to pesticides and the occurrence of aplastic anemia (RR=0.67, 95% CI=0.26–1.7). Unlike the studies from Thailand, subjects for this study were identified from death certificates rather than from a hospital-case registry, and occupations recorded on death certificates, rather than questionnaires, were used to evaluate potential exposure. The authors reported no relationship between trends in the use of organochlorine insecticides (including lindane) and the incidence of aplastic anemia.
A number of studies have examined the relationship between hematologic parameters and exposure to insecticides. Those studies have the potential to provide evidence to support conclusions on aplastic anemia; however, because they generally examined workers with continuing exposures, they do not provide information about