Epidemiological study (observational study)

Case-control study of occupational exposure to electric shocks and magnetic fields and mortality from amyotrophic lateral sclerosis in the US, 1991-1999 epidem.

By: Vergara X, Mezei G, Kheifets L

Published in: J Expo Sci Environ Epidemiol 2015; 25 (1): 65-71

Aim of study (acc. to author)

A case-control study was conducted in the USA to investigate the association between occupational exposure to electric shocks and magnetic fields and mortality from amyotrophic lateral sclerosis.

Endpoint/type of risk estimation

neurodegenerative diseases: amyotrophic lateral sclerosis

Type of risk estimation:

mortality

(odds ratio (OR))

Exposure

- electric injuries/electrocution
- occupational

Assessment

job exposure matrix: usual occupation as reported on death certificates was linked to job-exposure matrices for electric shocks and magnetic fields

Exposure groups

Group	Description
Reference group 1	non-electric occupations
Group 2	electric occupations
Group 3	electric occupations, not high electric shocks
Group 4	electric occupations, high electric shocks
Group 5	electric occupations, not high magnetic fields (< 0.3µmT)
Group 6	electric occupations, high magnetic fields (≥ 0.3µmT)
Reference group 7	non-welding occupations
Group 8	welding occupations
Group 9	welding occupations, not high electric shocks
Group 10	welding occupations, high electric shocks
Group 11	welding occupations, not high magnetic fields (< 0.3µmT)
Group 12	welding occupations, high magnetic fields (≥ 0.3µmT)
Reference group 13	electric shocks: low
Group 14	electric shocks: medium
Group 15	electric shocks: high
Reference group 16	magnetic field exposure: low
Group 17	magnetic field exposure: medium
Group 18	magnetic field exposure: high

Population

Group:
- men
- women
Age: ≥ 20 years
Observation period: 1991 - 1999
Study location: USA

Case group

Characteristics: all decedents with amyotrophic lateral sclerosis mentioned in death record
Data source: National Center for Health Statistics (NCHS), Center for Disease Control and Prevention

Control group

decedents with other deaths likely not related to electric shocks and magnetic fields
Selection:
- registry-based
Matching:
- sex
- area
- 5-year age group
- case:control = 1:10
Exclusion criteria: decedents with leukemia, brain tumor, other neurodegenerative diseases, electrocution

Study size

	Cases	Controls
Evaluable	5,886	57,667

Statistical analysis method:

conditional logistic regression

(adjustment:

education
ethnicity

)

Results (acc. to author)

A moderately increased mortality from amyotrophic lateral sclerosis was observed for those who worked within electric occupations (OR 1.23, CI 1.04-1.47). Exposure to electric shocks was inversely associated with mortality from amyotrophic lateral sclerosis: workers with high exposure (OR 0.73, CI 0.67-0.79) had a lower risk than workers with medium exposure (OR 0.90, CI 0.84-0.97). No consistent association between occupational magnetic field exposure and mortality from amyotrophic lateral sclerosis was found (high exposure: OR 1.09, CI 1.00-1.19; medium exposure: OR 1.09, CI 0.96-1.23). Exposure to electric shock or magnetic field exposure did not account for the association observed for electric occupations.
A decreased risk between welding occupations and mortality from amyotrophic lateral sclerosis was observed (OR 0.77, CI 0.55-0.89). Among welding occupations, an association similar in magnitude was observed for high and low electric shocks and magnetic field exposure as well as with adjustment for electric shocks, magnetic fields or both.
The authors concluded that an association between electric occupations and mortality from amyotrophic lateral sclerosis was observed which is consistent with previous publications. In the present study, neither electric shocks nor exposure to magnetic fields explained the association between electric occupations and amyotrophic lateral sclerosis.

Study funded by

Centers for Disease Control and Prevention (CDC), USA
National Institute for Occupational Safety and Health (NIOSH), USA

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