Number and incidence of drift events and cases. From 1998 through 2006, we identified 643 events and 2,945 illness cases associated with pesticide drift from agricultural applications (). Of these, 382 events (59%) and 791 cases (27%) were identified by SENSOR-Pesticides (excluding 60 events and 171 cases also identified by PISP), and 261 events (41%) and 2,154 cases (73%) were identified by PISP. Drift cases consisted of 53 definite (1.8%), 2,019 probable (68.6%), 823 possible (27.9%), and 50 suspicious (1.7%) cases. Among drift cases, 1,565 (53%) were nonoccupational and 1,380 (47%) were occupational. Agricultural workers accounted for 73% (n = 1,010) of the occupational cases. A total of 340 events (53%) occurred between May and August, and these involved 1,407 cases (48%).
The overall incidence rate of drift-related pesticide poisoning was 2.93 per million person-years (). The rates of nonoccupational and occupational drift-related pesticide poisoning were 1.56 and 2.89 per million persons-years, respectively. Among occupational cases, the rate was 114.3 for agricultural workers and 0.79 for all other workers. Among nonoccupational cases identified in California, the rate was 42.2 for residents in the five agriculture-intensive counties and 0.61 for residents of all other California counties (data not shown). The rate was highest in the western states for both nonoccupational and occupational cases (). In California, per 100,000 agricultural applications, 1.6 drift events and 11.8 cases were identified; per 10 million pounds applied, 1.9 events and 14.4 cases were identified (data not shown).
Number and incidence ratea of off-target drift events and pesticide poisoning cases by year, region, sex, and age, 11 states, 1998–2006.
The total annual incidence rate ranged from 1.39 to 5.32 per million persons over the 9-year time period (). Over time, the rate of drift cases involved in large events showed the same pattern as the rate of all drift cases, showing a spike every 3 years (). The rate of drift cases involved in small events varied within a narrow range from 0.49 to 1.11, and we found no significant rate change over this time period; however, for the five states that provided data for all 9 years, we found a significant decrease in the rate (i.e., an estimated 9% decrease per year; 95% CI, 3–15%; p = 0.004).
Incidence rate of pesticide poisoning associated with off-target drift exposure over time, 11 states, 1998–2006.
Men comprised 53% of all cases (). The rate by sex was similar among nonoccupational cases. For occupational cases, the rate was 1.25 times higher in male workers than in female workers but 2.89 times higher in female agricultural workers than in male agricultural workers. Among nonoccupational cases, children < 15 years of age accounted for 33% of cases with known age and showed the highest rate (1.88/million person-years; ).
Responsible pesticides, application targets, and application equipment. In 430 (67%) of 643 drift events, exposure was to pesticides from a single functional class (). Insecticides were the most commonly identified (31% of events), accounting for 23% (n = 678) of all cases. Fumigants were involved in only 8% of drift events but accounted for 45% (n = 1,330) of all cases. Organophosphorus compounds were the most common pesticide chemical class involved in drift events (28%). Most cases (66%) were exposed to toxicity I (high toxicity) pesticides.
Off-target drift events and pesticide poisoning cases by pesticide and application characteristics, 11 states, 1998–2006.
For the intended application targets, 71% of events involved applications to fruit, grain/fiber/grass, or vegetable crops (). Soil applications accounted for 9% of drift events and 45% of all cases. For application equipment, aerial applications (e.g., by airplane) were responsible for 39% of drift events, accounting for 24% of all cases. Chemigation (i.e., application via an irrigation system) or soil injectors were used in 7% of drift events and accounted for 44% of cases. All soil injector events and 95% of chemigation events involved the use of fumigants applied to soil (data not shown).
Location of exposure and health effects. Common exposure locations were private residences (44%) and farms/nurseries (37%; ). More than half of cases experienced ocular (58%) or neurological (53%) symptoms or signs, and illness severity was low for most cases (92%; ). Moderate/high severity illness was significantly associated with females, older age groups, and exposure to multiple active ingredients, before and after controlling for other case and pesticide characteristics (p < 0.05; ). Compared with fumigants, exposures to herbicides, insecticides, or multiple classes were significantly associated with moderate/high illness. lists 15 active ingredients most commonly found among drift cases and their distribution according to illness severity.
Location of exposure, health effects, and illness severity of drift cases (n = 2,945).
Illness severity by case and pesticide characteristics.
Fifteen most common active ingredients for drift cases and percentage of moderate/high severity.
Size of drift events.
Most drift events involved a single case (n
= 387, 60%). For multiperson events, 168 events (26% of the total) involved 2–4 cases, 78 events (12%) involved 5–29 cases, and 10 events (1.5%) involved ≥ 30 cases. provides details on the 10 largest events. Detailed investigation reports of some of these events are available elsewhere (Barry et al. 2010
; CDC 2004
; O’Malley et al. 2005
). The occurrence of large versus small events (events with ≥ 5 vs. < 5 cases) was significantly associated with the use of fumigants (compared with insecticides) and applications to soil, small fruit crops, or leafy vegetable crops (compared with other targets; p
< 0.05; ).
Ten largest drift events, 1998–2006.
Factors associated with large drift events (≥ 5 cases).
Contributing factors to drift incidents. Of 299 drift events with information on violations of pesticide regulations, 220 (74%) had one or more violations and accounted for 2,093 cases (89% of cases with violation information; ). However, not all of the observed violations may have directly contributed to the drift exposure. Factors contributing to the drift exposure were identified in 164 events, accounting for 1,544 (52%) cases. Common contributing factors identified for drift events included applicators’ carelessness near or over nontarget sites (e.g., flew over a house, did not turn off a nozzle at the end of the row), unfavorable weather conditions (e.g., high wind speed, temperature inversion), and poor communication between applicators or growers and others. Improper seal of the fumigation site (e.g., tarp tear, early removal of seal), which were identified in nine events, accounted for the largest proportion (60%) of cases with contributing factors identified.
Violation in and contributing factors to occurrence of drift incidents/exposures.
The distance between the application and exposure site was identified in 1,428 (48%) cases (). Occupational cases accounted for 68% of cases exposed within 0.25 miles of the application site, and nonoccupational cases accounted for 73% of cases exposed > 0.25 miles away.