AMERICAN JOURNAL OF INDUSTRIAL MEDICINE 51:883–898 (2008)

Acute Pesticide Poisoning Among Agricultural

Workers in the United States, 1998–2005

GeoffreyM. Calvert, MD, MPH,

1 Jennifer Karnik, MPH,1 Louise Mehler, PHD, MD,2

John Beckman, BS,

3 Barbara Morrissey, MS,4 Jennifer Sievert, BA,5

Rosanna Barrett, MPH,

6 Michelle Lackovic, MPH,7 Laura Mabee, BA,8

AbbySchwartz, MPH,

9 Yvette Mitchell, MS,10 and Stephanie Moraga-McHaley, MS11

Background Approximately 75% of pesticide usage in the United States occurs in

agriculture. As such, agricultural workers are at greater risk of pesticide exposure than

non-agricultural workers. However, the magnitude, characteristics and trend of acute

pesticide poisoning among agricultural workers are unknown.

Methods We identified acute pesticide poisoning cases in agricultural workers between the

ages of 15 and 64 years that occurred from 1998 to 2005. The California Department of

Pesticide Regulation and the SENSOR-Pesticides program provided the cases. Acute

occupational pesticide poisoning incidence rates (IR) for those employed in agriculture were

calculated, as were incidence rate ratios (IRR) among agricultural workers relative to nonagricultural workers.

Results Of the 3,271 cases included in the analysis, 2,334 (71%) were employed as

farmworkers. The remaining cases were employed as processing/packing plant workers

(12%), farmers (3%), and other miscellaneous agricultural workers (19%). The majority

of cases had low severity illness (N 1⁄4 2,848, 87%), while 402 (12%) were of medium

severity and 20 (0.6%) were of high severity. One case was fatal. Rates of illness among

various agricultural worker categories were highly variable but all, except farmers,

showed risk for agricultural workers greater than risk for non-agricultural workers by an

order of magnitude or more. Also, the rate among female agricultural workers was almost

twofold higher compared to males.

Conclusion The findings from this study suggest that acute pesticide poisoning in the

agricultural industry continues to be an important problem. These findings reinforce the

need for heightened efforts to better protect farmworkers from pesticide exposure. Am. J.

Ind. Med. 51:883–898, 2008. Published 2008 Wiley-Liss, Inc.{

KEY WORDS: pesticides; surveillance; poisoning; agriculture; farmworkers

Published 2008 Wiley-Liss,Inc.

{

This article is a US Government work and, as such, isin

the public domain in the United States of America.

9

Division of Environmental Health, Michigan Department of Community Health, Lansing,

Michigan 10Bureau of Occupational Health, NewYork State Department of Health,Troy, NewYork

11NewMexico Occupational Health Registry, University of NewMexico, Albuquerque,

NewMexico

The findings and conclusions inthisreport are those of the authors and do not necessarily

represent the views of the National Institute for Occupational Safety and Health or each

author’s state agency.

*Correspondence to: Geoffrey M. Calvert, National Institute for Occupational Safety and

Health, 4676 Columbia Parkway, R-17, Cincinnati, OH 45226. E-mail: jac6@cdc.gov

Accepted 23 June 2008

DOI10.1002/ajim.20623. Published online in Wiley InterScience

(www.interscience.wiley.com)

1

Division of Surveillance, Hazard Evaluations and Field Studies, National Institute for

Occupational Safety and Health, Centers for Disease Control and Prevention, Cincinnati,

Ohio2

Department of Pesticide Regulation, California Environmental Protection Agency, Sacramento, California 3

Public Health Institute, Oakland, California

4

Office of Environmental Assessments,Washington State Department of Health,Olympia,

Washington 5

Environmental and Injury Epidemiology and Toxicology Branch, Texas Department of

State Health Services, Austin,Texas 6

Florida Department of Health,Tallahassee, Florida

7

Louisiana Department of Health and Hospitals, NewOrleans, Louisiana

8

Office of Environmental Public Health, Oregon Department of Human Services, Portland,

Oregon
INTRODUCTION

Pesticides are widely used in agriculture to control insects,

microorganisms, fungi, weeds, and other pests. The control of

these pests serves to increase crop yield and decrease manual

labor [Litchfield, 2005]. In 2000 and 2001, over 5 billion

pounds of pesticides were used annually throughout the world.

The United States was responsible for 24% of this total usage

[Kiely et al., 2004]. Within the US, the agricultural industry

accounts for approximately 75% of the annual poundage used.

Farming is an essential component of our economy, but

agricultural workers suffer elevated rates of injuries, hearing

loss, and respiratory disease [Rust, 1990; Linaker and

Smedley, 2002; Tak and Calvert, 2008]. Pesticides are also

an important source of injury and illness among farmers and

farm workers [Calvert et al., 2004]. Previous work has

suggested that the agricultural industry’s disproportionately

high pesticide use puts farmers and farm workers at greater

risk of pesticide exposure than others [Reeves and Schafer,

2003; Calvert et al., 2004]. Farmers and farmworkers may be

exposed by mixing, loading and applying pesticides, or while

performing duties not involved with pesticide application

(e.g., weeding, harvesting, thinning, irrigating, or planting).

Recognizing the need for increased worker protections

from pesticide exposures, the U.S. Environmental Protection

Agency (EPA) promulgated rules in 1974 known as the

Worker Protection Standard for Agricultural Pesticides

(WPS; 40 CFR 170) and aimed at reducing pesticide

exposures among agricultural workers. However, by 1992,

EPA estimated that hired farmworkers alone experienced up

to 10,000–20,000 illnesses and injuries from pesticide

exposures each year [US EPA, 1992] and concluded that

the WPS was inadequate in its requirements and scope of

coverage. That year, EPA revised and expanded the WPS

rules to include changes in labeling, coverage of more

workers and agricultural operations, prohibition of employer

retaliation against workers attempting to comply with the

standard, and the following requirements: notification of

workers about pesticide applications; restriction of re-entry

into pesticide-treated areas; and, provision of personal

protective equipment (PPE), decontamination supplies,

emergency assistance, and pesticide safety training. Detailed

information on the magnitude, characteristics and trend of

acute pesticide poisoning since the revised WPS went into

effect in 1995 are unavailable.

The National Institute for Occupational Safety and Health

(NIOSH) developed the Sentinel Event Notification System

for Occupational Risks-Pesticides (SENSOR-Pesticides) program [Calvert et al., 2001] to monitor risks from pesticide

exposure. Data from this program are available beginning in

1998, when standardized definitions for cases and data

elements were adopted [Calvert et al., 2001]. The California

Department of Pesticide Regulation (CDPR) has a similar

surveillance program that has been tracking pesticide-related

illnesses for more than 30 years [Calvert et al., 2001]. To assess

the magnitude, characteristics and trend of acute pesticide

poisoning among agricultural workers in the United States

since the revised WPS went into effect in 1995, an analysis of

data obtained from these surveillance systems was performed.

MATERIALS AND METHODS

Data were obtained on individuals age 15 through 64 who

developed an acute pesticide-related illness or injury and who

were employed in the agricultural industry when the occupational pesticide exposure occurred. Census 1990 industry

codes (1990 CIC) and Census 2002 industry codes (2002 CIC)

were used to identify cases employed in agriculture [US

Bureau of the Census, 1992; US Census Bureau, 2005]. The

agricultural industry was defined as: agricultural production,

excluding livestock (1990 CIC 1⁄4 010; 2002 CIC1⁄4 0170);

agricultural production, including livestock (1990 CIC 1⁄4 011;

2002 CIC1⁄4 0180); and agricultural services (1990

CIC 1⁄4 030; 2002 CIC 1⁄4 0290). All agricultural industry cases

also had their occupation coded using Census 1990 occupation

codes (1990 COC) and Census 2002 occupation codes (2002

COC) [US Bureau of the Census, 1992; US Census Bureau,

2005]. Agricultural occupations included: farmworkers (1990

COC 1⁄4 477, 479, 484; 2002 COC 1⁄4 6050, 6120, 8710, 8960);

farmers (1990 COC 1⁄4 473–476; 2002 COC 1⁄4 0200, 0210);

processing/packing plant workers (1990 COC 1⁄4 488, 699;

2002 COC 1⁄4 6040, 7830, 7850, 8640, 8720, 8800, 8860,

9640); and, other miscellaneous agricultural workers (workers

employed in agriculture but whose 1990 COC and 2002 COC

did not match any of those specified for the other three

agricultural occupations). A pesticide handler was defined as

an individual who mixed, loaded, transported and/or applied

pesticides, or an individual who repaired or maintained

pesticide application equipment at the time of pesticide

exposure (insufficient information was available to determine

pesticide handler status for 68 individuals). This analysis

excluded illnesses associated with non-occupational exposures and illnesses associated with intentional (e.g., suicidal,

malicious intent) exposures.

Cases under 15 years of age and those 65 years and older

were omitted from analysis. The age range was chosen a

priori, and is considered to include the vast bulk of workers

who are gainfully employed. A total of 66 cases age 65 and

older were identified but not included in this analysis (this

represents a rate of 13/100,000 agricultural workers age 65

and older). Furthermore, Current Population Survey (CPS)

data, the source of our denominator data, are unavailable on

workers less than 15 years of age.

Data Sources

Data for this analysis were obtained from CDPR and the

SENSOR-Pesticides program. State health departments in

884 Calvert et al.
ten states participated in the SENSOR-Pesticides program

and contributed data. These ten state health departments were

the: Arizona Department of Health, California Department of

Public Health (CDPH), Florida Department of Health,

Louisiana Department of Health and Hospitals, Michigan

Department of Community Health, New Mexico Department

of Health (through an agreement with the University of New

Mexico), New York State Department of Health, Oregon

Department of Human Services, Texas Department of State

Health Services, and the Washington State Department of

Health. The time frame for data availability varied according

to state agency. The years of data availability are provided in

Table I. Each of these agencies maintains its own passive

population-based surveillance system for acute pesticiderelated illness or injury with occasional outreach to potential

reporters to stimulate reporting (e.g., contacting poison

control centers to encourage them to report or reviewing

physician reports submitted to workers’ compensation

insurance carriers to identify eligible cases) [Calvert et al.,

2001, 2004]. Each agency obtains case reports from many

different sources. All require physician reporting of pesticide-related illness cases. Other sources of case reports vary

by state and include poison control centers, state agencies

with jurisdiction over pesticide use (e.g., departments of

agriculture), and workers’ compensation claims. Because

each state removes any personal identifiers from the data

prior to submission to the Centers for Disease Control and

Prevention this study was exempt from consideration by the

federal Human Subjects Review Board.

Once a case report is received, the state agency determines

whether the subject was symptomatic and whether the

involved chemical is a pesticide. If so, attempts are made to

interview the poisoned subject or their proxy to obtain details

on the poisoning event, and any medical records are requested.

Besides identifying, classifying, and tabulating pesticide

poisoning cases, the states periodically perform in-depth

investigations of pesticide-related events, and develop interventions aimed at particular industries or pesticide hazards.

Cases obtained from CDPR were cross-referenced with

cases from the CDPH based on age, gender, date of exposure,

and pesticide name. Matching cases were assumed to be the

same individual and were counted only once.

Information Available on Each Case

Data collected for each case by the SENSOR-Pesticides

and CDPR surveillance systems include case demographics,

signs and symptoms of illness or injury, illness severity, EPA

toxicity category, identity of implicated pesticides and the

target (e.g., crop) of their application (if any), information on

factors that may have contributed to the pesticide exposure

that precipitated illness, and the source of the case report.

EPA evaluates the toxicity of and assigns a toxicity

category to each pesticide product. The categories range

from I to IV, with I representing the most toxic and IV the

least toxic substances [US EPA, 1975]. The toxicity category for each case was obtained by the relevant state agency

conducting pesticide poisoning surveillance. When toxicity

category data was not given, the category was determined

by NIOSH based on standardized criteria from a dataset

provided by EPA. Cases exposed to more than one pesticide

product were assigned the toxicity category representing the

pesticide product with the greatest toxicity.

Case Definition

A standardized case definition is used by all participating

SENSOR-pesticides states. Cases of acute pesticide poisoning are included in the analyses if they were classified

as definite, probable, possible or suspicious. A classification

category is assigned to a case based on three factors: (1) the

strength of evidence that a pesticide exposure occurred; (2)

whether adverse health effects were observed by a healthcare

professional versus being self-reported; and (3) the presence

of sufficient evidence that the known toxicology of the agent

was consistent with the observed health effects. Cases

exposed to pesticides for which there is limited toxicological

data were classified as suspicious [CDC, 2001a]. CDPR uses

a comparable case definition [CDPR, 2006]. In this article,

acute pesticide poisoning and acute pesticide-related illness

and injury are used interchangeably.

Illness severity was assigned to all cases using standardized criteria which were based on signs and symptoms,

medical care received, and lost time from work [CDC,

2001b]. Low severity illness/ injury consist of illnesses and

injuries that generally resolve without treatment and

where minimal time (<3 days) is lost from work. Such cases

typically manifest as eye, skin and/or upper respiratory

irritation. Moderate severity illness/injury consists of nonlife-threatening health effects that are generally systemic and

require medical treatment. No residual disability is detected,

and time lost from work is less than 6 days. High severity

illness/injury consists of life threatening health effects that

usually require hospitalization, involve substantial time lost

from work (>5 days), and may result in permanent impairment or disability. Death pertains to fatalities resulting from

exposure to one or more pesticides.

Data Analysis

SAS v. 9.1 was used for data management and analysis

[SAS Institute Inc, 2003]. Chi square statistical analyses

were performed on categorical data. Incidence rates (IR) for

acute occupational pesticide poisoning were calculated

for those employed in agriculture. Rates were calculated

for occupational categories within agriculture, for each year

studied, by age group, and for three geographic regions in the

US. The numerator represents the number of relevant cases

Pesticide Poisoning Among Agricultural Workers 885
TABLE I. Data on Demographics, PesticideToxicity, Pesticide Handler, Pesticide Functional Class, and ApplicationTarget for 3,271Acute Pesticide Poisoning

Cases in the Agricultural Industry by Severity Category,1998^2005

Fatal, N High Severity, N Medium Severity, N Low Severity, N Total, N (%)a

Total 1 20 402 2,848 3,271

Age

15^17 0 0 5 19 24 (1)

18^24 0 1 82 521 604 (18)

25^34 0 2 109 786 897 (27)

35^44 0 7 103 630 740 (23)

45^54 0 3 59 358 420 (13)

55^64 1 5 28 138 172 (5)

Unknown 0 2 16 396 414 (13)

State where illness identified (years of data availability)

Arizona (1998^1999) 0 0 4 17 21 (1)

California (1998^2005) 1 10 274 2,235 2,520 (77)

Florida (1998^2005) 0 0 23 109 132 (4)

Louisiana (2001^2005) 0 4 14 27 45 (1)

Michigan (2001^2005) 0 1 7 14 22 (1)

NewMexico (2005 only) 0 0 2 10 12 (1)

NewYork (1998^2005) 0 0 6 7 13 (1)

Oregon (1998^2005) 0 0 6 37 43 (1)

Texas (1998^2005) 0 3 40 146 189 (6)

Washington (2001^2005) 0 2 26 246 274 (8)

Gender

Female 0 6 114 934 1,054 (32)

Male 1 14 288 1,886 2,189 (67)

Unknown 0 0 0 28 28 (1)

Year exposed

1998 0 2 64 358 424 (13)

1999 1 1 85 337 424 (13)

2000 0 4 64 315 383 (12)

2001 0 0 30 236 266 (8)

2002 0 0 26 576 602 (18)

2003 0 0 43 279 322 (10)

2004 0 11 35 396 442 (14)

2005 0 2 55 351 408 (12)

Toxicity categoryb

I 1 11 232 1,418 1,662 (51)

II 0 1 68 599 668 (20)

III and IV 0 6 82 792 880 (27)

Unknown 0 2 20 39 61 (2)

Pesticide handler

Yesc 1 10 190 867 1,068 (33)

No 0 10 200 1,925 2,135 (65)

Unknown 0 0 12 56 68 (2)

Pesticide functional classd

InsecticidesEall 1 10 210 1,540 1,761 (54)

Insecticides only 0 7 115 747 869 (27)

Insecticides combined 1 3 95 793 892 (27)

FungicidesEall 1 4 90 734 829 (25)

Fungicides only 0 2 28 147 177 (5)

Fungicides combined 1 2 62 587 652 (20)

886 Calvert et al.
captured by CDPR and SENSOR-Pesticides from 1998 to

2005. Denominator data, including employment counts and

the hours worked estimate, were obtained from the CPS

[BLS, 2007]. The hours worked data were used to derive fulltime equivalent (FTEs) estimates, with one FTE equivalent to

2,000 hr worked. Denominator data correspond to the states

and time periods of data availability (Table I). Although

rates were calculated with the two denominator estimates

(employment counts and FTE estimates), the rates calculated

with FTEs as the denominator are given prominence as they

have previously been shown to be conceptually preferable

over the use of raw employment counts [Ruser, 1998]. The

comparison group consisted of all workers not employed in

agriculture. IR for workers employed in non-agricultural

industries were similarly calculated, with the numerator and

denominator data obtained from the same agencies (SENSOR/CDPR and CPS, respectively) that provided the data on

agricultural workers. Finally, incidence rate ratios (IRR)

were calculated to determine the risk of acute pesticide

poisoning while working in agriculture. This ratio was

calculated by dividing the IR among agricultural workers

with that among non-agricultural workers. A ratio greater

than one suggests an increased risk in farmers or farmworkers, while a ratio less than one suggests a decreased risk.

Confidence intervals (95% CIs) were calculated for each rate

ratio as described by Rothman [1986].

RESULTS

From 1998 to 2005, 3,271 case reports met inclusion

criteria (Table I). Of these, 1,078 (33%) were identified by the

SENSOR-Pesticides program and 2,193 (67%) originated

from CDPR (527 cases were identified by both SENSOR and

CDPR and were included in the CDPR total only). There

were 1,942 separate pesticide exposure events, 1,762 of

which (91%) involved only one ill agricultural worker. Of the

DisinfectantsEall 0 2 56 389 447 (14)

Disinfectants only 0 2 48 238 288 (9)

Disinfectants combined 0 0 8 151 159 (5)

HerbicidesEall 0 1 56 400 457 (14)

Herbicides only 0 1 42 318 361 (11)

Herbicides combined 0 0 14 82 96 (3)

FumigantsEall 0 4 44 416 464 (14)

Fumigants only 0 4 44 416 464 (14)

Fumigants combined 0 0 0 0 0 (0)

Other 0 1 18 130 149 (5)

Application target

Fruit crops 0 3 112 1,047 1,162 (36)

Vegetable crops 0 2 45 411 458 (14)

Soil 0 2 20 316 338 (10)

Grains, grasses and fiber crops 0 1 58 201 260 (8)

Landscape/ornamental 0 1 18 159 178 (5)

Undesired plant 0 0 6 74 80 (2)

Beverage crops 0 0 7 35 42 (1)

Crops that cross categories 0 0 6 32 38 (1)

Building structure/surface/space 0 1 8 35 44 (1)

Oil crops 0 0 5 15 20 (1)

Miscellaneousfield crops 0 0 8 11 19 (1)

Veterinary (livestock or domestic) 0 0 4 13 17 (1)

Other 1 2 18 182 203 (6)

Not applicable 0 4 55 161 220 (7)

Unknown 0 4 32 156 192 (6)

a

Percentages may not sum to100 due to rounding.

b

Acute pesticide toxicity category as defined by the U.S. EPA.

c

A pesticide handler was defined as an individual who mixed, loaded, transported and/or applied pesticides, or an individual who repaired or maintained pesticide application

equipment at the time of pesticide exposure.

d

Cases may be exposed to more than one functional class. The rows labeled with ‘‘combined’’ pertain to cases exposed to more than one pesticide active ingredient, some of

which belong to the pesticide functional class specified in the row label and others belonging to other pesticide functional classes.

TABLE I. (Continued )

Fatal, N High Severity, N Medium Severity, N Low Severity, N Total, N (%)a

Pesticide Poisoning Among Agricultural Workers 887
180 (9%) multi-victim events, the median number of ill

agricultural workers was 3 (range 2–123). The number of

pesticide exposure events decreased over the time period

studied but the average number of cases per event increased

(in 1998 there were 308 events with an average of 1.4 cases

per event whereas in 2005 there were 209 events with an

average of 2.0 cases per event).

Description of the Three Largest Events

More than three quarters of the cases (N 1⁄4 2,520, 77%)

occurred in California. Among these cases, we found a small

number of events that exposed large numbers of agricultural

workers. In two separate 2002 incidents, irritant vapors

drifted from soil treatments with metam-sodium and caused

low severity illness in 123 vineyard workers and in 72

workers at a carrot processing facility, respectively [see

O’Malley et al., 2005 for detailed information on the event

involving 72 workers]. The second largest incident occurred

in 2004, when 121 peach harvesters became ill after exposure

to drift from an application of methamidophos and mancozeb

to a nearby potato field. Most of these workers experienced

low severity illness (N 1⁄4 111, 92%), and the other 10 workers

(8%) experienced moderate severity illness.

Incidence Rates

Tables II and III and Figure 1 summarize IRs for

agricultural workers and non-agricultural workers from 1998

to 2005. Overall, the average annual IR among agricultural

workers was 53.6/100,000 FTEs and 1.38/100,000 FTEs

among all non-agricultural workers combined (IRR 1⁄4 38.9

95% CI 37.2, 40.6). Agricultural workers’ annual rates

fluctuated between 33.8/100,000 FTEs (2001) and 79.9/

TABLE II. Incidence Rates by Industry,Year of Exposure, Age Group and US Region for 3,271Acute Pesticide Poisoning Cases,1998^2005

Agricultural workers Non-agricultural workers

Incidence rate

ratiod Count

FTE

estimatea

Incidence

rateb Count

FTE

estimatea

Incidence

ratec

Year of exposure

1998 424 790,837 53.6 762 40,792,468 1.9 28.7

1999 424 781,985 54.2 656 42,040,152 1.6 34.7

2000 383 781,654 49.0 577 41,041,774 1.4 34.9

2001 266 787,481 33.8 552 49,456,474 1.1 30.3

2002 602 753,595 79.9 598 49,110,280 1.2 65.6

2003 322 756,610 42.6 694 50,151,930 1.4 30.8

2004 442 735,270 60.1 716 50,989,934 1.4 42.8

2005 408 710,851 57.4 638 53,000,554 1.2 47.7

Age group (years)

15^17 24 99,364 24.2 69 3,140,858 2.2 11.0

18^24 604 792,852 76.2 851 43,536,103 2.0 39.0

25^34 897 1,392,263 64.4 1,246 92,090,687 1.4 47.6

35^44 740 1,601,894 46.2 1,303 106,763,138 1.2 37.9

45^54 420 1,276,042 32.9 968 89,437,936 1.1 30.4

55^64 172 935,868 18.4 356 41,614,845 0.9 21.5

Unknow n 414 E E 400 E E E

USregion

Weste 2,858 3,168,485 90.2 3,556 149,655,538 2.4 38.0

Southf 366 2,258,774 16.2 1,225 141,962,800 0.9 18.8

Eastg 45 671,024 7.0 412 84,965,229 0.5 13.8

Total 3,271 6,098,283 53.6 5,193 376,583,567 1.4 38.9

a

FTE, full-time equivalent.

b

Incidence rate per100,000 FTEs. Includes agricultural workers in Arizona, California, Florida, Louisiana, Michigan, New Mexico, New York, Oregon,Texas, and Washington. c

Incidence rate per100,000 FTEs. Includes non-agricultural workers in Arizona, California, Florida, Louisiana, Michigan, New Mexico, New York, Oregon,Texas, and Washington. d

Compares the rate of acute pesticide poisoning among agricultural workers for a given year with non-agricultural workers. Cases are identified by participating SENSORPesticides states and CDPR. All IRRs were significantly elevated (P <0.0001). e

Arizona, California, NewMexico, Oregon, and Washington.

f

Florida, Louisiana, and Texas.

g

Michigan, NewYork.

888 Calvert et al.
100,000 FTEs (2002), driven primarily by the occurrence of

large California events (Fig. 1). Limiting the analysis to the

five states (California, Florida, New York, Oregon, Texas)

that provided data for all 8 years had little effect on the plot in

the Figure 1. By US geographic region, the IR for agricultural

workers was highest in the West. The rates in the West were

largely driven by California and Washington State, where the

rates were 100.8 and 113.0/100,000 FTEs, respectively.

Information on age was available for 87% of the cases

(N 1⁄4 2,857; Table I). The median age was 33 years (range

TABLE III. Incidence Rates by Occupation for 3,271 Acute Pesticide Poisoning Cases in the Agricultural Industry,

1998^2005

Occupation Number Percent FTE estimatea Incidence rateb

FarmworkerEall 2,334 71 3,119,402 74.8

FarmworkerEmale 1,620 69 2,625,146 61.7

FarmworkerEfemale 701 30 494,256 141.8

Farmer 89 3 1,852,030 4.8

FarmerEmale 80 90 1,510,632 5.3

FarmerEfemale 9 10 341,398 2.6

Processing/packing plant worker 394 12 108,646 362.6

Processing/packing plant workerEmale 108 27 21,094 512.0

Processing/packing plant workerEfemale 279 71 87,552 318.7

All other agricultural occupations 454 14 1,018,205 44.6

All other agricultural occupationsEmale 381 84 674,521 56.5

All other agricultural occupationsEfemale 65 14 343,684 18.9

Totalc 3,271 100 6,098,283 53.6

TotalEmale 2,189 67 4,831,393 45.3

TotalEfemale 1,054 32 1,266,890 83.2

a

FTE, full-time equivalent.

b

Incidence rates per100,000 FTEs. Includes agricultural workers in Arizona, California, Florida, Louisiana, Michigan, New Mexico, New

York, Oregon,Texas, and Washington.

c

Sex was unknown for 28 cases (farmworkers 1⁄413, processing/packing plant worker 1⁄4 7, all other agricultural occupations 1⁄4 8).

FIGURE 1. Incidence rates for acute pesticide poisoning cases among agricultural and non-agricultural workers by year,

age15^64 years,1998 ^2005.

Pesticide Poisoning Among Agricultural Workers 889
15–64), and over half of the cases were between the ages of

25 and 44 years (N 1⁄4 1,637, 57%). The IR was highest among

agricultural workers age 18–24 years (76.2/100,000 FTEs;

Table II).

Because agricultural workers employed in the states

and time periods covered in this study worked 2,173 hr

per year on average, using FTEs in the denominator produced

rates that were approximately 7% lower compared to when

employment counts were used in the denominator. In

contrast, because non-agricultural workers worked 1,935 hr

per year on average, using FTEs in the denominator produced

rates that were approximately 4% higher compared to when

employment counts were used in the denominator. The

overall average annual IR among agricultural workers using

employment counts in the denominator was 57.6/100,000

workers, and was 1.33/100,000 FTEs among all nonagricultural workers combined (IRR 1⁄4 43.2, 95% CI 41.4,

45.1).

Occupations of the Affected Agricultural

Workers

Most of the 3,271 affected agricultural workers were

employed as farmworkers (N 1⁄4 2,334, 71%; Table III). The

394 affected processing/packing plant workers (12%)

represented a disproportionately large share of people so

employed, while farmers (N 1⁄4 89, 3%) seemed less at risk

than hired agricultural workers. Most of the ‘‘other

miscellaneous agricultural workers’’ were employed as pest

control operators (N 1⁄4 255, 56%). Because CPS data for pest

control operators were too sparse (e.g., in 1999 and 2001 no

CPS data were available for this occupation), IRs were not

calculated for this occupation.

Gender was reported for all but 28 (1%) of the cases.

Males predominated in each occupational category except

processing/packing plant workers. Paradoxically, IRs were

higher among female than male farmers and farmworkers,

but higher among male than female processing/packing plant

workers. Females were less likely than males to be pesticide

handlers (females 1⁄4 8%, males 1⁄4 45%, P < 0.001). Information on race and ethnicity was available for 727 cases (22%).

A total of 502 (69%) were Hispanic, 187 (26%) were nonHispanic white, 12 (2%) were black, and the remaining 26

(4%) recorded various other races.

Severityand Description of Fatal Case

A vast majority of the illnesses were of low severity

(2,848 cases, 87%), while 402 (12%) were of medium

severity and 20 (0.6%) were high severity (Table I). One case

was fatal. The fatal case occurred in 1999 and involved a 59-

year-old Hispanic male who was employed as an irrigator and

farmworker supervisor. He was found dead in an orange

grove in California, with packages of hotdogs and packets of

methomyl near his body. This led investigators to suspect he

had violated regulations by opening water-soluble methomyl

packets and using the potent carbamate insecticide to

contaminate hot dogs for use as bait to kill coyotes. His

autopsy found a small amount of methomyl in his gastric

contents but none in his blood. His blood and bile also

contained a relatively large concentration of benzothiazole,

an industrial chemical and a metabolite of cyprodinil

(a toxicity category III fungicide). The large concentration

of benzothiazole was suggestive of chronic exposure, or

heavy acute exposure at least 24 hr earlier. The medical

examiner concluded that the cause of death was likely due to

an interaction between the methomyl and cyprodinil. The

source of the exposure to benzothiazole or cyprodinil was not

known. Whether the exposures were accidental or intentional

(i.e., suicidal) could not be distinguished.

Signs and Symptoms

Table IV lists the signs and symptoms most often

reported in this cohort. It also provides information on the

health effects among those exposed to the four pesticide

chemical classes most commonly involved in illness.

Pesticides Responsible for Illness

Information on the pesticides responsible for illness is

provided in Tables I, IV and V. Insecticides (alone or in

combination with other pesticides) were implicated in more

than half of the illnesses (N 1⁄4 1,761, 54%). Cholinesterase

inhibitors (organophosphates and N-methyl carbamates)

were prominent among the insecticides (N 1⁄4 892, 51%),

particularly chlorpyrifos (N 1⁄4 190), methamidophos

(N 1⁄4 130), dimethoate (N 1⁄4 84), malathion (N 1⁄4 78), and

diazinon (N 1⁄4 70). Over half of the cases (N 1⁄4 1,662, 51%)

were exposed to toxicity category I pesticides, the most toxic

category as defined by EPA (Table I). We found little

variation in illness severity by pesticide category.

Activityat Time of Exposure

Information on activity at time of pesticide exposure

was available for 3,203 (98%) of the affected workers. Of

these, 33% (N 1⁄4 1,068) were pesticide handlers and 67%

(N 1⁄4 2,135) were doing routine work not involved with a

pesticide application. Most of the handlers (71%) were

exposed while making applications. Among the 2,135 doing

routine work, half were exposed to off-target drift of pesticide

from a nearby application (N 1⁄4 1,068), and 35% (N 1⁄4 744)

had contact with pesticide residues present on a treated

surface (e.g., plant material or treated animal).

Table I lists the targets to which pesticides were applied

in incidents that resulted in human illness. Among the

890 Calvert et al.
fruit crops, the most common application targets were

small fruits (e.g., grapes; N 1⁄4 529, 46%), tree nuts (N 1⁄4 181,

16%), citrus fruits (N 1⁄4 175, 15%), and pome fruits

(e.g., apples; N 1⁄4 151, 13%). Among the most common

vegetable crop targets were root and tuber vegetables

(e.g., onions and potatoes; N 1⁄4 185, 40%), leafy vegetables

(N 1⁄4 180, 39%) and fruiting vegetables (e.g., eggplant,

tomatoes, and peppers; N 1⁄4 48, 10%). Among grain, grass

and fiber crops, the most common pesticide application

targets were cotton (N 1⁄4 140, 54%), and cereal grains

(N 1⁄4 61, 23%).

Factors That Contributed to Pesticide

Exposure

We identified factors that contributed to pesticide

exposure in 1,926 (59%) of the cases (Table VI). The most

common factors identified were off-target drift (N 1⁄4 1,216,

63%), early reentry into a recently treated area (N 1⁄4 336,

17%), and use in conflict with the label (N 1⁄4 319, 17%). In

992 (30%) cases, no obvious contributory factors could be

identified (e.g., restricted entry interval was observed but

worker still became ill; wore all required PPE but still

TABLE IV. Illness Characteristics by Pesticide Chemical Class for 3,271Acute Pesticide Poisoning Cases in the Agricultural Industry,1998^2005

Signs and symptoms

Pesticide chemical classa,b

Alla,

N 1⁄4 3,271 (%)

Cholinesterase

inhibitors, N 1⁄4 892 (%)

Pyrethroids,

N 1⁄4182 (%)

Inorganics,

N 1⁄4 567 (%)

Dithiocarbamates,

N 1⁄4 512 (%)

Nervous/sensory 1,743 (53) 672 (75) 120 (66) 241 (43) 237 (46)

Headache 1,268 (39) 499 (56) 94 (52) 164 (29) 185 (36)

Dizziness 708 (22) 297 (33) 39 (21) 88 (16) 85 (17)

Muscle weakness 243 (7) 126 (14) 10 (5) 29 (5) 23 (4)

Blurred vision 204 (6) 86 (10) 8 (4) 34(6) 29(6)

Paresthesias 198 (6) 76 (9) 15 (8) 31 (5) 25 (5)

Muscle pain 98 (3) 44 (5) 7 (4) 7 (1) 15 (3)

Diaphoresis 94 (3) 59 (7) 6 (3) 8(1) 7(1)

Salivation 63 (2) 48 (5) 3 (2) 2 (<1) 19 (4)

Fasciculation 47 (1) 32 (4) 3 (2) 3 (1) 3 (1)

Confusion 46 (1) 19 (2) 1 (1) 3 (1) 2 (<1)

Gastrointestinal 1,300 (40) 510 (57) 91 (50) 174 (31) 188 (37)

Nausea 1,063 (33) 438 (49) 74 (41) 131 (23) 152 (30)

Vomiting 582 (18) 261 (29) 39 (21) 73 (13) 91 (18)

Abdominal pain/cramping 371 (11) 161 (18) 15 (8) 34 (6) 75 (15)

Diarrhea 148 (5) 80 (9) 8 (4) 8 (1) 17 (3)

Ocular 1,300 (40) 272 (30) 54 (30) 243 (43) 297 (58)

Irritation/pain/inflammation 1,112 (34) 208 (23) 48 (26) 222 (39) 262 (51)

Lacrimation 443 (14) 92 (10) 14 (8) 51 (9) 166 (32)

Conjunctivitis 80 (2) 8 (1) 5 (3) 23 (4) 1 (<1)

Dermatologic 1,077 (33) 235 (26) 57 (31) 191 (34) 96 (19)

Pruritis 580 (18) 106 (12) 26 (14) 125 (22) 50 (10)

Rash 571 (17) 98 (11) 17 (9) 126 (22) 64 (13)

Erythema 349 (11) 52 (6) 14 (8) 76 (13) 27 (5)

Irritation/pain 321 (10) 81 (9) 34 (19) 48 (8) 23 (4)

Respiratory 1,074 (33) 329 (37) 56 (31) 232 (41) 152 (30)

Upperrespiratory pain/irritation 645 (20) 183 (21) 35 (19) 142 (25) 103 (20)

Dyspnea 408 (12) 115 (13) 19 (10) 91 (16) 60 (12)

Cough 278 (9) 67 (8) 5 (3) 75 (13) 32 (6)

Cardiovascular 211 (6) 77 (9) 7 (4) 43 (8) 31 (6)

Chest pain 131 (4) 45 (5) 4 (2) 32 (6) 18 (4)

Tachycardia 33 (1) 17 (2) 1 (1) 2 (<1) 3 (1)

a

More than one sign/symptom may be reported by a case, and therefore the sum of the specific clinical effects may not equal the total number of system effects. b

Cases may be exposed to more than one chemical class.Columns include cases exposed to the labeled chemical class only as well as those exposed to mixtures containing that

and other chemical classes.

Pesticide Poisoning Among Agricultural Workers 891
TABLE V. Fifteen Most Common Active Ingredientsfor 3,271Acute Pesticide Poisoning Cases in the Agricultural Industry by Severity Category,1998^2005

Active ingredient

Functional class

(chemical class)

High severity/

fatal Moderate severity Low severity N (%)a

Sulfur Insecticide and fungicide (inorganic) 2 45 421 468 (14)

Metam-sodium Fumigant (dithiocarbamate) 1 5 279 285 (9)

Glyphosate Herbicide (phosphonate) 3 25 223 251 (8)

Mancozeb Fungicide (dithiocarbamate) 1 17 184 202 (6)

Chlorpyrifos Insecticide (organophosphate/cholinesterase inhibitor) 0 33 157 190 (6)

Sodium hypochlorite Disinfectant (halogen) 2 35 149 186 (6)

Methamidophos Insecticide (organophosphate/cholinesterase inhibitor) 1 10 119 130 (4)

Abamectin Insecticide (microbial) 0 18 108 126 (4)

Imidacloprid Insecticide (neonicotinoid) 4 5 104 113 (3)

Methomyl Insecticide (N-methyl carbamate/cholinesterase inhibitor) 1 7 101 109 (3)

Myclobutanil Fungicide (triazole) 1 11 97 109 (3)

Propargite Insecticide (sulfite ester, inhibits oxidative phosphorylation) 0 21 77 98 (3)

Spinosad Insecticide (derived fromSaccharopolyspora spinosa) 1 10 85 96 (3)

Methyl bromide Fumigant (halocarbon) 2 29 60 91 (3)

Dimethoate Insecticide (organophosphate/cholinesterase inhibitor) 4 6 74 84 (3)

a

Percentages do not sum to100, as not all cases are included in this table.

TABLE VI. FactorsThat Contributed to Pesticide Exposure and/or Illness for 3,271Acute Pesticide Poisoning Cases in the Agricultural Industry by Severity

Category,1998^2005

Exposure/illness factora Medium or higher severity, N (%) Low severity, N Total, N (%)

All factors combined 219 (11) 1,707 1,926 (59)

Drift 118 (10) 1,098 1,216 (37)

Early reentry 41 (12) 295 336 (10)

Use in conflict with label 40 (13) 279 319 (10)

Failure to userequired equipment 19 (12) 139 158 (5)

Oral notification of pesticide application not provided 9 (6) 143 152 (5)

PPE not worn 19 (16) 98 117 (4)

Training not provided or inadequate (excludes applicators) 30 (29)c 75 105 (3)

Hazard communication or other OSHAviolation 9 (9) 86 95 (3)

Transport for care not provided 5 (6) 84 89 (3)

Application site not posted/notification posters incorrect 3(4) 81 84 (3)

Decontamination facilities inadequate 16 (26)c 46 62 (2)

Unsafe equipment/failure 8 (14) 49 57 (2)

Inadequaterecord keeping 7 (20) 28 35 (1)

Worker not told of health effects caused by pesticides 0 (0) 32 32 (1)

Person in treated area during application 2 (10) 19 21 (1)

Unspecified worker protection standard violation 3 (15) 17 20 (1)

PPE in poorrepair 3 (23) 10 13 (<1)

FIFRA-other and unspecifiedb 6 (27)c 16 22 (1)

None identified 126 (13) 866 992 (30)

Unknown 78 (22) 275 353 (11)

a

One factor was identified for1,279 cases.Two or more factors were identified for 647 cases.

b

Includes situations when a licensed applicator was not on site(N 1⁄41) and when an applicator was not properly trained or supervised (N 1⁄4 9). c

The proportion with medium or higher severity among cases with the factor of interest was significantly greater than the proportion with medium or higher severity in all other

cases (P <0.05).Those with insufficient information to identify factors (i.e., unknown category) were excluded from this analysis.

892 Calvert et al.
became ill; all pesticide label requirements appeared to have

been followed). Compared to cases where no obvious

contributory factors could be identified, identification of a

contributory factor was not found to be significantly associated with severity of illness (P 1⁄4 0.33). For 353 (11%)

cases, insufficient information was available to identify

factors that may have contributed to the pesticide exposure.

Among the 2,367 cases with personal protection

equipment (PPE) usage information, 1,157 (49%) wore

PPE (Table VII). Women were far less likely to wear PPE

(females 1⁄4 27%, males 1⁄4 40%, P < 0.01). Pesticide handlers

were more likely to use PPE (65% overall, 66% among men

and 51% among women) compared to non-handlers (21%

overall, 18% among men and 26% among women). Those

exposed to toxicity category II pesticides were more likely to

wear PPE (61%) then those exposed to toxicity category I or

III /IV pesticides (53% and 54%, respectively). Table VII

also provides information on the health effects experienced

by those who used each type of protective equipment.

Compared to those who used no protective equipment or had

unknown information on its use, those who used protective

equipment were less likely to have health effects involving

the nervous, gastrointestinal and respiratory systems, but

were more likely to have ocular and dermatologic health

effects.

Report Source

Case reports were received from many different sources.

The three leading sources of case reports were workers’

compensation (N 1⁄4 1,109, 34%), other government agencies

(e.g., county health departments and the state department of

agriculture; N 1⁄4 901, 28%), and poison control centers

(N 1⁄4 407, 12%). A variety of sources accounted for the

remaining cases including health care professionals, employers, worker representatives (union, legal services), and selfreport. The specific number of cases reported by these other

sources is unavailable. Females were more likely to have

been reported by one of these other sources (females 1⁄4 41%,

males 1⁄4 23%, P < 0.01), and less likely to be identified by

workers’ compensation (females 1⁄4 25%, males 1⁄4 39%,

P < 0.01) or poison control centers (females 1⁄4 8%, males 1⁄4 15%, P < 0.01). Females and males were equally likely

to have been reported by other government agencies (28%).

DISCUSSION

It is important to conduct surveillance of acute occupational pesticide poisoning to determine whether policies,

practices and regulations are effective in preventing hazardous pesticide exposures. National estimates of hospitalized

pesticide poisonings in the 1970s and early 1980s, including

agricultural workers, are available [Keefe et al., 1985, 1990];

but to the best of our knowledge this is the first detailed multistate assessment of both hospitalized and non-hospitalized

acute pesticide poisoning among agricultural workers. Our

findings indicate that despite strengthening of the WPS in

1995, agricultural workers continue to have an elevated risk

for acute pesticide poisoning. The pesticide poisoning

incidence among US agricultural workers was found to be

39 times higher than the IR found in all other industries

combined.

Improvement Compared to the 1980s

Although there was not a clear trend in the rates of

poisoning during the time period that we studied, there is

evidence to suggest that the counts of pesticide poisoning

TABLE VII. Illness Characteristics byType of Protective Equipment Used1998^2005

Type of protective

equipment

Number that used

protective equipment

Of workers who used protective equipment,the number (%) who

had signs/symptoms involving these organs/systems

Nervous/sensory Gastro-intestinal Ocular Respiratory Dermatologic

Any PPE 1,157 557 (48) 404 (35) 472 (41) 301 (28) 437 (38)

Air-purifyingrespirator 261 121 (46) 91 (35) 92 (35) 49 (19) 94 (36)

Dustmask 40 16 (40) 12 (30) 19 (48) 18 (45) 15 (38)

Chemical resistant gloves 700 306 (44) 208 (30) 293 (42) 150 (21) 254 (36)

Chemical resistant clothing 542 230 (42) 177 (33) 214 (39) 105 (19) 213 (39)

Chemical resistant boots 367 170 (46) 110 (30) 152 (41) 63 (17) 127 (35)

Cloth/leather gloves 298 192 (64) 138 (46) 92 (31) 114 (38) 140 (47)

Goggles/eye protection 488 193 (40) 126 (26) 198 (41) 80 (16) 196 (40)

Engineering controlsa 100 48 (48) 34 (34) 23 (23) 20 (20) 41 (41)

No or unknown PPE useb 0 1,186 (56) 896 (42) 828 (39) 773 (37) 640 (30)

a

Engineering controls included such things as enclosed tractor cabs or closed mixing/loading systems.

b

A total of 2,114 individuals used no protective equipment or had unknown information on use of protective equipment.

Pesticide Poisoning Among Agricultural Workers 893
cases among agricultural workers have decreased since the

1980s. Mehler et al. [1992] reported an annual average of 723

cases of pesticide illness or injury in California arising from

agricultural establishments from 1982 to 1990. In contrast,

the California surveillance programs reported an average of

315 cases per year from 1998 to 2005. The numbers are not

entirely comparable. Mehler characterized poisoning cases

as being agricultural if the poisoned subject was a worker and

the exposure arose from an agricultural establishment. Her

definition included non-agricultural workers (e.g., truck

drivers, construction workers, school employees), while we

included only workers employed in agriculture.

True Incidence Remains Uncertain:

Comparison With Data From the

Bureau of Labor Statistics, the

National Agricultural Workers Survey,

and the Agricultural Health Study

In order to put our findings in perspective, acute

pesticide poisoning annually accounts for a small percentage

of the total occupational illnesses experienced by agricultural

workers. The 2005 Bureau of Labor Statistics (BLS) survey

of illnesses and injuries (SOII), which excludes agricultural

production establishments with 10 employees or fewer,

reports an annual injury rate of 5.7% and an annual illness

rate of 0.4% (3% of which involve poisonings) among

workers in farming, forestry and fishing [Myers, 2007]. Most

of these illnesses consisted of dermatitis, respiratory conditions, and other conditions not specified (e.g., musculoskeletal conditions arising from cumulative trauma). We report a

rate of pesticide poisoning five times higher than the SOII rate

for all poisonings. This may indicate that pesticide poisonings

are concentrated among the small establishments excluded

from SOII, that under-reporting to SOII is more extreme than

SENSOR-pesticide under-ascertainment, or that SENSORpesticide classification standards accept a large number of

cases that BLS does not count.

Data from the National Agricultural Workers Survey

(NAWS), by contrast, suggest an incidence of acute pesticide

poisoning among agricultural workers [US Department of

Labor, 2004] an order of magnitude greater than that found in

this study. NAWS is a nationally representative annual survey

of US crop workers conducted by the US Department of

Labor. In 1999, NAWS included questions to determine if

crop workers were poisoned by pesticides. This information

was collected in two parts. First NAWS asked the crop worker

if they were exposed to pesticides by ‘‘having them sprayed

or blown on you,’’ ‘‘spilled on you,’’ or ‘‘when cleaning

or repairing containers or equipment used for applying or

storing pesticides.’’ NAWS then asked if the crop worker

became ‘‘sick or [had] any reaction because of this incident.’’

Our analysis of these data found that 3.2% of crop workers

acknowledged exposure during the previous 12 months, of

whom 43.4% reported getting sick or having a reaction. That

is, 1.4% of US crop workers attributed health effects such as

skin problems (59%), eye problems (24%), nausea/vomiting

(30%), headache (26%), and numbness/tingling (12%) to

pesticide exposure during the preceding 12 months. In a

separate NAWS question, 0.6% of all US crop workers

reported that in the last 12 months they had ‘‘received

medical attention by a doctor or nurse due to pesticide

exposure.’’ To our knowledge, neither these nor similar

questions to assess the incidence of pesticide poisoning

were included in NAWS surveys before or after 1999. In

comparison, we found an average annual acute occupational

pesticide poisoning IR of 0.05% among all agricultural

workers, and 0.07% among farmworkers.

Acute pesticide poisoning IR were also assessed among

farmers participating in the Agricultural Health Study

(AHS), a prospective cohort study sponsored by the National

Institutes of Health (i.e., the National Cancer Institute and the

National Institute of Environmental Health Sciences) and

EPA [AHS, 2007]. The AHS cohort consists of 52,395

farmers, 32,347 spouses of these farmers, and 4,916

commercial pesticide applicators residing in Iowa or North

Carolina. In a nested case–control analysis involving 16,416

farmers/pesticide applicators who were interviewed by

telephone in 1999–2000, 54 (0.33%) reported ‘‘an incident

with fertilizers, weed killers, or other pesticides that caused

an unusually high personal exposure’’ in the previous

12 months that resulted in physical symptoms [Bell et al.,

2006]. Among these 54 individuals, only 7 (13%, or .04% of

the entire subcohort) sought medical care. In contrast,

we found an average annual acute occupational pesticide

poisoning IR of 0.005% among farmers. However, as was

observed in our study, the findings from AHS and NAWS

suggest that the risk of pesticide poisoning is lower among

farmers compared to farmworkers.

The true incidence of pesticide poisoning among

agricultural workers remains uncertain. Our findings (51/

100,000) fall between the low SOII estimate (less than 10/

100,000) and the high rates elicited by NAWS interviews

(1,400/100,000 symptomatic, 600/100,000 sought medical

care).

Limitations

One of this study’s major limitations is that underreporting compromises, to varying degrees, all the surveillance systems that provided the data for this analysis. Factors

that contribute to under-reporting include: affected people

not seeking care, or consulting care providers outside the

jurisdiction of surveillance programs; misdiagnosis of this

uncommon condition; and health care provider neglect of

legal requirements to report. The rates provided should be

considered low estimates of the magnitude of acute pesticide

poisoning among agricultural workers.

894 Calvert et al.
Disproportionate numbers of agricultural workers probably are deterred from seeking health care by lack of health

insurance [US Department of Labor, 2005], unfamiliarity with

workers’ compensation benefits or inability to qualify for

them, and fear of job loss if they miss time from work to seek

health care [Das et al., 2001; Arcury and Quandt, 2007],

as well as concerns related to immigration status. Similarly,

a variety of interrelated problems may lead health care

professionals to misdiagnose acute pesticide poisoning.

Health professionals rarely receive much training in environmental toxicology generally or on pesticide poisoning

specifically [Schenk et al., 1996]. Consequently, they may

not collect a pesticide exposure history, which is necessary to

make a diagnosis of acute pesticide poisoning [Balbus et al.,

2006]. Pesticide poisoning is relatively rare in developed

countries, and its signs and symptoms often resemble those of

more common conditions, which may be diagnosed preferentially. The difficulty and delays of receiving reimbursement

through workers’ compensation may also bias health care

providers against diagnosing and reporting pesticide poisoning. Even among those cases correctly diagnosed, some cases

may escape report to public health authorities through

ignorance of the requirement (despite the fact that 30 states

have a mandatory reporting system of occupationally related

pesticide poisoning [Calvert et al., 2001]) or because the

health care professionals fear that their patients may be

subject to retaliation. Other cases may go unreported because

many farmworkers immigrate from Mexico [US Department

of Labor, 2005], and some poisoned Mexican farmworkers

may prefer to visit physicians in Mexico where cultural and

linguistic barriers are removed and fees are lower [US EPA,

1992; Arcury and Quandt, 2007]. Our state-based surveillance partners received only nine reports of pesticide

poisoning cases managed outside the US.

Another limitation in our study was that information was

incomplete for some reported cases. Most cases lacked

information on race and ethnicity. Missing information

could lead to misclassification of severity, if not all signs and

symptoms were reported, or to inappropriate exclusion of the

case. More detailed information on the affected worker’s

activities, pesticide exposures and health effects might have

increased our case totals. Some cases in this report may be

false-positives, with compatible symptoms that are coincidental with but not caused by pesticide exposure. Finally,

information on factors that contributed to illness was

identified in only 1,926 (59%) cases. In many cases

a timely and definitive investigation into the factors responsible for exposure and illness was not possible due to

insufficient investigatory resources and/or because of tardy

notification of the exposure to state authorities.

Rates of pesticide poisoning may also be distorted by

inaccuracy in estimates of population at risk. The size of the

agricultural worker population, including farmworkers and

processing/packing plant workers, is difficult to estimate for

several reasons, including the transient employment of many

seasonal and migrant farmworkers, migration into and out of

the United States in a manner that is not entirely predictable,

and the tendency of many farmworkers to avoid government

contact [Rust, 1990]. Our agricultural worker population

estimates were derived from the CPS, which is conducted by

the BLS and the United States Census Bureau. The CPS goes

to great lengths to capture reliable workforce data [Bureau of

Labor Statistics, 2002]. Nevertheless, a population seeking to

escape detection could well be under-counted, leading to

inflated apparent rates of illness/injury. Finally, illness rates

for those known to have occupational pesticide exposure are

not available because the numbers or workers exposed to

pesticides are unknown.

Reasons for Higher Poisoning Rates in

Western States

Rates of both agricultural and non-agricultural acute

pesticide poisoning are higher in the western states as

compared to the south and eastern regions of the United

States. It is credible that labor-intensive Western agriculture

may impose excess risk for acute pesticide poisoning illness,

but it is also important to note that California (especially the

CDPR program) and Washington have well established,

longstanding and experienced state-based surveillance programs with higher staffing levels compared to other states

participating in the SENSOR-Pesticides program [Calvert

et al., 2004]. In addition, these states were much more likely

to be notified about cases through the state workers’

compensation system (in Washington State 76% of the cases

were so identified; in California 34% of reports were

provided by physicians to a workers’ compensation insurance carrier). In contrast, only two other states identified

cases through their state workers’ compensation system:

Oregon and Texas (7% and 4%, respectively, of cases in these

states were so identified).

Higher Poisoning Rates Among Female

Agricultural Workers

Female agricultural workers experienced nearly twice the

risk of pesticide poisoning of male agricultural workers (Table

III), a finding that was quite unexpected. Before indulging in

speculation about possible differences in susceptibility, risk of

exposure, or rate of ascertainment, we plan to perform more

detailed analyses by geographic region, activity at time of

exposure, pesticide, protective equipment, and severity.

Higher Poisoning Rates Among

Processing/Packing Plant Workers

Processing/packing plant workers were found to have

the highest acute pesticide poisoning IR compared to all other

Pesticide Poisoning Among Agricultural Workers 895
agricultural occupations. Many farms are increasing the

amount of food processing that is performed on site [National

Research Council and Institute of Medicine, 2008]. This is

due to a variety of factors, including the advent of new

technology, quest for improved quality control and freshness,

and a desire to increase profit. The types of food processing

activities performed on farms include cleaning, sorting,

packing, and cooling/freezing. Among the 394 poisoned

processing/packing plant workers, the pesticides most

commonly responsible for illness were fumigants (N 1⁄4 151,

38%), disinfectants (N 1⁄4 151, 38%), and insecticides

(N 1⁄4 73, 19%). The fumigant exposures were commonly

related to drift from a nearby field (N 1⁄4 111), the disinfectant

exposures where commonly related to malfunction of

disinfecting equipment (N 1⁄4 74) and cleaning produce in

disinfectant solutions (N 1⁄4 31) and the insecticide exposures

were commonly related to pesticide residue present on the

produce (N 1⁄4 37). Because the WPS only covers workers

involved in the production of agricultural plants, processing/

packing plant workers may not covered by WPS.

Chronic Health Effects Associated With

Acute Pesticide Poisoning

In addition to acute morbidity with it attendant costs in

health care resources, and time lost from work and normal

daily activities, acute pesticide poisoning is also associated

with chronic adverse health sequelae. For example organophosphate poisoning has been found to be associated with

deficits in neurobehavioral and neurosensory function

[Steenland et al., 1994]. In addition, the Agricultural Health

Study found that those who sought medical care for pesticide

poisoning or who experienced an incident involving

‘‘unusually high’’ pesticide exposure had an increased risk

for chronic neurologic symptoms (Kamel et al. 2005). These

‘‘unusually high’’ pesticide exposures, which are labeled by

the authors as high pesticide exposure events (HPEE), result

in acute symptomatic illness about 50% of the time [Bell

et al., 2006]. Those who ever experienced an HPEE also had

an increased risk for farmers lung (Hoppin et al. 2006). A

non-significant elevated risk for prostate cancer was

observed among those who had ever experienced an HPEE

(odds ratio 1⁄4 1.11, 95% CI 1⁄4 0.8, 1.6) [Alavanja et al., 2003].

To our knowledge, the AHS has not published findings on any

other associations between HPEE and cancer.

Recommendations

The most common factors that contributed to pesticide

exposure included off-target drift, early reentry into a treated

area, and use in conflict with the pesticide label. These

findings and the observations of other investigators [Arcury

et al., 2001] suggest that improved compliance with and

enforcement of existing pesticide regulations could achieve

important improvements in safety. Measures to minimize

drift (including equipment specifications, establishment of

buffer zones, and limitations on maximum wind speed

conditions during an application) seem likely to provide the

greatest benefit. Our finding that 992 (30%) cases had no

obvious factors contributing to exposure suggests that

pesticide regulations and label requirements may also need

to be enhanced. Additionally, reduced-risk pest control

measures such as integrated pest management should be

adopted, which can achieve reductions in pesticide exposure

and misuse [National Research Council, 2000]. The high

poisoning rates observed among processing/packing plant

workers and the increased amount of food processing

performed on farms suggests that processing/packing plant

workers should be covered under the WPS.

Given the limitations in this analysis, improved statebased surveillance programs for pesticide-related illness are

also needed. A comprehensive system needs to address the

limitations described above including: agricultural workers

and health care providers need to recognize the pesticiderelatedness of the illness; disincentives to receiving health

care, including lack of health insurance, must be overcome; the

costs of evaluation and treatment of acute occupational

pesticide poisoning should be paid for by workers’ compensation; health care providers need to make timely reports to

pesticide poisoning surveillance systems; and, surveillance

systems need to optimize access to and use of workers’

compensation data, poison control center data and data from

other state agencies with jurisdiction over pesticides.

CONCLUSION

Agricultural workers are at increased risk of acute

pesticide poisoning in comparison to non-agricultural workers, particularly through drift, early reentry into a treated

area, and use in conflict with the label. The IR was almost

twofold higher in female agricultural workers compared to

males. In addition to acute intoxication, pesticide poisoning

may also lead to chronic adverse health sequelae. Improved

compliance with and stringent enforcement of laws and

regulations regarding pesticide applications are needed.

Alternative pest control measures such as integrated pest

management reduce the use of pesticides and therefore the

potential for adverse health effects.

ACKNOWLEDGMENTS

Funding to support this study was provided by NIOSH,

EPA, and the state agencies that contributed data.

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