Publication No. 94-102

April 1994

Request for Assistance in Preventing Organic Dust Toxic

Syndrome1

The National Institute for Occupational Safety and Health2

The National Institute for Occupational Safety and

Health (NIOSH) requests assistance in preventing

organic dust toxic syndrome (ODTS), an acute

respiratory illness in agricultural workers who inhale

contaminated organic dust. This Alert describes four

case reports in which a total of 29 agricultural workers

developed ODTS following inhalation of organic dusts

contaminated with microorganisms. Information about

ODTS is urgently needed by agricultural workers and

employers, cooperative extension agents, rural

veterinarians, physicians, and other health care providers.

NIOSH therefore requests that editors of trade journals,

safety and health officials, labor unions, and agricultural

employers bring this Alert to the attention of all workers

who are at risk. Your assistance in this effort will help

prevent occupational disease among the 3.4 million

agricultural workers in the United States-one of the

stated goals of the 1991 Surgeon General’s Conference

on Agricultural Safety and Health [DHHS 1992].

Agricultural workers are at risk for developing

respiratory illness from exposure to inhaled dusts. One

of the most common illnesses is ODTS, a respiratory and

systemic illness that may follow exposures to heavy

concentrations of organic dusts contaminated with

microorganisms [doPico 1986; Parker et al. 1992]. An

estimated 30% to 40% of workers exposed to organic

dusts will develop the disease [dopico 1986; RaskAndersen 1989].

Despite its common occurrence among agricultural

workers, ODTS is not a widely recognized illness

because only serious cases or clusters of cases are likely

to come to a physician’s attention. ODTS is a general

term that includes all of the following conditions:

Precipitin-negative farmer’s lung disease [Edwards

et al. 1974]

Pulmonary mycotoxicosis [Emanuel et al. 1975]

Grain fever in grain elevator workers [doPico et

al. 19821

Silo unloader’s syndrome [Pratt and May 1984]

Mill fever in cotton textile workers [Rylander et

al. 1987]

Inhalation fever [Rask-Andersen and Pratt 1992]

ODTS typically occurs where a large amount of

organic dust is present in the air. The syndrome often

occurs in small clusters and affects most individuals who

are exposed to heavy concentrations of organic dust

contaminated with microorganisms [Brinton et al. 1987].

ODTS appears to result from inhaling particles and

toxins produced by microorganisms such as gramnegative bacteria (Pseudomonas species, Enterobacter

agglomerans, and Klebsiella species), thermophilic

organisms (Aspergillus fumigatus and Micropolyspora

faeni), and fungi [Schenker et al. 1991]. Endotoxin1 is

a com-mon component of organic dust in agriculture

[Olenchock et al. 1990; Dutkiewicz 1987] and may be

involved in the development of ODTS.

Although the focus of this Alert is on ODTS,

agricultural workers should be aware that they are at risk

for other important respiratory illnesses or hazards such

as the following:

Silo filler’s disease, an acute toxic inflammation of

the lung caused by exposure to oxides of nitrogen in

freshly filled silos [Grayson 1956; Horvath et al.

1978]

1. This document is NIOSH Publication No. 94-102. Publication date: April 1994.

2. National Institute of Occupational Safety and Health, Department of Health and Human Services, 200 Independence Avenue, SW, Washington,

DC, 20201. Phone: (800) 356-4674.

Disclaimer: Mention of the name of any company or product does not constitute endorsement by the National Institute for Occupational Safety

and Health.
Request for Assistance in Preventing Organic Dust Toxic Syndrome Page 2

Farmer’s lung disease (or hypersensitivity

pneumonitis), an immunologic lung response

involving microbial antigens in moldy hay

[Campbell 1932; Parker et al. 1992]

Bronchitis

Death by asphyxiation (suffocation)

Inhalation of toxic gases (in manure pits, for

example) [NIOSH 1990]

CURRENT OSHA REGULATIONS

Cotton dust is the only specific agricultural dust for

which the Occupational Safety and Health

Administration (OSHA) has a standard. This standard

protects workers in general industry against byssinosis,

a chronic lung disease [29 CFR2 1910.1043]. OSHA

also has a standard for nonspecific dusts: 15 milligrams

per cubic meter (mg/m3

) for total dust and 5 mg/m3 for

respirable dust [29 CFR 1910.1000].

NIOSH has recommended exposure limits for cotton

dust, grain dust, and wood dust [NIOSH 1992b], but

these limits may not adequately protect workers exposed

to organic dusts contaminated with microorganisms.

HEALTH EFFECTS OF ORGANIC DUST

Agricultural workers may develop ODTS after

inhaling dust from contaminated organic materials. The

syndrome is characterized by fever occurring 4 to 12

hours after exposure and flu-like symptoms such as

general weakness, headache, chills, body aches, and

cough. Shortness of breath may also occur.

Listening to the chest usually reveals normal

breathing sounds, and chest X-rays are usually normal.

Pulmonary function may be impaired, and an increase in

the number of white blood cells is common. Antibodies

commonly associated with certain allergic lung diseases

such as farmer’s lung are usually not present.

No specific therapy is needed to treat ODTS.

However, the syndrome may often be misdiagnosed as

acute bronchitis, influenza, or farmer’s lung disease,

which may lead to unnecessary therapy with antibiotics

or anti-inflammatory medication. ODTS usually

disappears within 24 hours to a few days after the

worker is removed from exposure. Repeated episodes of

ODTS can occur after reexposure to contaminated

organic dusts. No deaths from ODTS have been

reported.

ODTS CASE REPORTS

The following cases highlight examples of ODTS.

Case No. 1: Nine workers affected

Eleven male workers, aged 15 to 60 years, moved

800 bushels of oats from a poorly ventilated storage bin

in Alabama [Parker et al. 1988]. The oats were reported

to contain pockets of powdery white dust. Work

conditions were described as extremely dusty, and all

workers wore single-strap disposable masks while inside

the bin. The workers shoveled the oats for 8 hours in

groups of two or three for shifts of 20 to 30 minutes.

Within 4 to 12 hours, all nine who worked inside the bin

became ill with fever and chills, chest discomfort,

weakness, and fatigue. Eight reported shortness of

breath, six had nonproductive coughs, five complained

of body aches, and four developed headaches. The two

workers who remained outside the storage bin developed

no symptoms. Six of the ill workers saw a doctor within

the first 2 days of symptoms. The following abnormal

physical signs were reported: body temperature greater

than 100.4°F (38.0°C) in two workers, crackle sounds in

the lungs of two workers, and wheezing sounds in one

worker. Chest X-rays were normal in all six workers.

Symptoms disappeared in all affected workers in 2 to 12

days.

Airborne dust generated in the laboratory from the

bulk oats contained 39.5 mg/m3 of respirable dust.

Endotoxin content in the respirable dust was elevated to

325.7 endotoxin units/mg of dust.

Despite an initial diagnosis of farmer’s lung disease,

the rate of illness among those who entered the bin

(100%, or 9 of 9) is typical of ODTS.

Case No. 2: One worker affected

A previously healthy 52-year-old man entered an

emergency room with a fever of 101.8°F, body aches,

and marked difficulty in breathing 12 hours after

shoveling composted wood chips and leaves [Weber et

al. 1990]. He was treated with oral glucocorticoids and

improved over 3 days. Blood tests did not show that he

was suffering from farmer’s lung disease.

Using respiratory protection, investigators recreated

the exposure and made extensive environmental

measurements. Peak exposures to respirable dust were

greater than 80 mg/m3 of air. Endotoxin concentrations

ranged from 244 to 16,300 endotoxin units/m3

-

concentrations previously associated with illness.
Request for Assistance in Preventing Organic Dust Toxic Syndrome Page 3

High concentrations of gram-negative bacteria were also

present [Olenchock et al. 1991].

Case No. 3: Fourteen workers affected

(silo unloader’s syndrome)

A retrospective study of hospital visits for farmassociated lung injury in a rural county in New York

over an 11-year period revealed 26 cases of respiratory

illness in 23 individuals [Pratt and May 1984]. Fourteen

of these individuals suffered fever of short duration.

Illness was most often associated with a 1 - to 3-hour

respiratory exposure that occurred during the preparation

of silos for mechanical unloading. During removal of

the moldy top silage, the workers developed burning in

the eyes and throat, headache, and cough. They

attributed these symptoms to the white powder or "fog"

arising from the moldy material. High fever, chest

discomfort, weakness, and nonproductive cough followed

within 4 to 12 hours. Blood tests failed to show that

these workers suffered from farmer’s lung disease.

A subsequent environmental study of five silos [May

et al. 1986] revealed that workers unloading silos

encounter total dust concentrations ranging from 0.2 to

138mg/m with concentrations at the silo base generally

similar to those in the headspace. Respirable dust

concentrations ranged from 0.2 to 24 mg/m3

, and

microorganism counts ranged from 105 to 109

/M3.

Thermophilic bacteria were the most prevalent organisms

of those cultured.

Case No. 4: Five workers affected

Five workers at a municipal golf course became ill

with an influenza-like syndrome within hours of

manually unloading a trailer truck filled with wood chips

[CDC 1986]. The wood chips were stored in an

enclosed, 40-foot trailer. Eleven workers participated in

the unloading process. Although fresh chips had been

ordered, the vendor included old chips that had been

stored in the front of the trailer for approximately 1 year.

Chips unloaded from the front were visibly

contaminated, and growth cultures revealed a wide

variety of bacteria and fungi.

All five workers who became ill had worked in very

dusty conditions without respiratory protection while

unloading the front of the trailer. The onset of illness

ranged from 4 to 16 hours after beginning work. None

of the workers were hospitalized, but one reported to a

local emergency room, and two were too ill to work the

following day. Within 48 hours, symptoms were greatly

improved; within 72 hours, all affected workers had

completely recovered.

The six workers who did not become ill included

three who had unloaded fresh chips from the back of the

trailer, one supervisor who had briefly checked on the

unloading process, and two workers who finished

unloading the front of the trailer the next morning using

air-purifying respirators.

CONCLUSIONS

The cases described in this Alert reveal the

seriousness of exposure to contaminated organic dust

among agricultural workers and others. Because many

agricultural workers find it difficult to seek medical

attention and because many physicians fall to recognize

occupational respiratory diseases, ODTS is probably

much more common than documented.

Recommendations

Minimizing Risk

Agricultural workers and employers should minimize

the risk of exposure to organic dusts by taking the

following precautions:

Be aware of the health effects of breathing organic

dust. Symptoms of ODTS occur 4 to 12 hours after

exposure and may include fever, weakness,

headache, chills, body aches, cough, and shortness

of breath.

Inform your doctor about recent dust exposures

when seeking treatment for respiratory illness.

Carefully harvest and store agricultural products to

minimize spoilage.

Use automated or mechanized equipment to move

decayed materials.

Use local exhaust ventilation and wet methods of

dust suppression to minimize exposure to organic

dusts. For example, adding a quart of water to the

cut side of bedding hay or straw before chopping is

an effective method for reducing dust levels (but

avoid overusing water) [NIOSH 1992c].

Use the following engineering controls to reduce the

dust exposure of silo unloaders [Jensen et al. 1993]:

Design the silo to provide for product turnover

and to provide unfavorable conditions for

microbial growth.

Design the conveyor to prevent spills of material

and to ventilate dust effectively.
Request for Assistance in Preventing Organic Dust Toxic Syndrome Page 4

Use ventilated loading spouts when filling

Table 1. NIOSH recommended respiratory protection for

workers exposed to organic dust

Type of respirator* APF**

Any air-purifying respirator with a highefficiency particulate air filter10

Any powered, air-purifying respirator with a

high-efficiency particulate air filter or,

25

Any supplied-air respirator equipped with a

hood or helmet and operated in a continuousflow mode

25

Any air-purifying, full-facepiece respirator with

a high-efficiency particulate air filter

50

Any powered, air-purifying respirator with a

tight-fitting facepiece and high-efficiency

particulate air filter

50

Any supplied-air respirator equipped with a

half-mask and operated in a pressuredemand or other positive-pressure mode

1,000

Any supplied-air respirator equipped with a

full facepiece and operated in a pressuredemand or other positive-pressure mode

2,000

Any self-contained breathing apparatus

equipped with a full facepiece and operated in

a pressure demand or other positive-pressure

mode

10,000

Any supplied-air respirator equipped with a

full facepiece and operated in a pressuredemand or other positive-pressure mode in

combination with an auxiliary self-contained

breathing apparatus operated in a pressuredemand or other positive-pressure mode

10,000

* Only NIOSH/MSHA-certified equipment should be

used.

** Assigned protection factor. The APF is the

minimum anticipated level of protection provided by

each type of respirator [NIOSH 1987b]. For

example, an APF of 10 means that the respirator

should reduce the air concentration of dust by a

factor of 10 (or to 10% of the concentration without

respiratory protection).

trucks and railroad cars with silage.

Use appropriate respirators approved by NIOSH and

the Mine Safety and Health Administration (MSHA)

when exposure to organic dust cannot be avoided

(see the following section on respiratory protection).

Do not wear contaminated work clothes inside the

home. Prevent exposure of family members to dusts

and other toxic materials by removing contaminated

clothes outside.

RESPIRATORY PROTECTION

Respirators should not be used as the only means of

preventing or minimizing exposures to airborne

contaminants. NIOSH recommends that workers be

protected by controlling dust at its source and by using

controls such as ventilation and wet dust suppression.

However, when exposure to organic dust cannot be

avoided, engineering controls should be supplemented

with the use of appropriate NIOSH/MSHA-approved

respirators.

Agricultural activities may generate a wide range of

respirable dust concentrations. For example, respirable

dust concentrations during bedding chopping have been

measured at 1.6 to 2.5 mg/m3 [Olenchock et al. 1990],

whereas they may be as high as 24 mg/m3 during silo

unloading [May et al. 1986]. Working in confined

spaces or enclosed locations can increase dust

concentrations.

Because of this wide range of potential exposures

and because there are no applicable exposure limits for

organic dusts contaminated with microorganisms, NIOSH

recommends that exposed workers wear the most

practical respirator with the highest assigned protection

factor (APF). Table 1 lists NIOSH-recommended

respirators and their APFs. Air-purifying respirators

should be worn with high-efficiency particulate air

(HEPA) filters.

Powered, air-purifying respirators (PAPRs) are the

most protective type of air-purifying respirator. Workers

exposed to organic dusts have been adequately protected

by PAPRs [Lenhart and Reed 1989; Clark 1986;

Anderson et al. 1989; van Assendelft et al. 1985] and

less effectively protected by other types of air-purifying

respirators [Lenhart and Cole 1993; Mu ̋ller-Wening and

Repp 1989; Dykewicz et al. 1988; Solley and Hyatt

1980].

For additional information about respirator selection,

consult the NIOSH Respirator Decision Logic [NIOSH

1987b]. Workers should use respirators certified by

NIOSH and MSHA [NIOSH 1992a].

When respirators are used, the employer must

establish a comprehensive respiratory protection program

as outlined in the NIOSH Guide to Industrial Respiratory

Protection [NIOSH 1987a] and as required in the OSHA
Request for Assistance in Preventing Organic Dust Toxic Syndrome Page 5

respiratory protection standard [29 CFR 1910.134].

Important elements of these programs are as follows:

An evaluation of the worker’s ability to perform

work while wearing a respirator

Regular training of personnel

Periodic environmental monitoring

Respirator fit testing

Maintenance, inspection, cleaning, and storage

Selection of appropriate respirators certified by

NIOSH and MSHA

Employers should evaluate the respiratory protection

program regularly.

The principal contributors to this Alert were Karl J.

Musgrave, D.V.M; John E. Parker, M.D.; Stephen A.

Olenchock, Ph.D.; and Robert M. Castellan, M.D., of the

NIOSH Division of Respiratory Disease Studies.

Comments, questions, or requests for additional

information should be directed to

Dr. Gregory Wagner

Director, Division of Respiratory Disease Studies

944 Chestnut Ridge Road

Morgantown, WV 26505-2888

Telephone (304) 291-4474

For more information about NIOSH health hazard

evaluations, technical assistance, and other research and

support activities concerning lung diseases in agricultural

workers, contact the following:

Coordinator, Respiratory Disease Hazard Evaluation

and Technical Assistance Program

Division of Respiratory Disease Studies

NIOSH

944 Chestnut Ridge Road

Morgantown, WV 26505-2888

Telephone: (304) 291-4203

We greatly appreciate your assistance in protecting the

health of U.S. workers.

Richard A. Lemen, Ph.D.

Acting Director, National Institute for Occupational

Safety and Health Centers for Disease Control and

Prevention

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1. A cell-wall component of gram-negative bacteria.

2. Code of Federal Regulations. See CFR in references.