Bypassing the selection rule in choosing controls for a case-control study

Sensory impairments, problems of balance and accidental injury at work: a case-control study

OBJECTIVES

Sensory impairments are becoming increasingly common in the workforces of Western countries. To assess their role in occupational injury, and that of disorders of balance, we undertook a case-control study.

METHODS

Using the Clinical Practice Research Datalink, which documents all medical consultations, referrals and diagnoses in primary care for 6% of the British population, we identified 1348 working-aged patients who had consulted medical services over a 22-year period for workplace injury (cases) and 6652 age-matched, sex-matched and practice-matched controls. Risks were assessed by conditional logistic regression, for earlier recorded diagnoses of visual impairment, common eye diseases, hearing loss, perforated ear drum, non-acute otitis media and disorders of balance.

RESULTS

In all, 173 (2.2%) participants had an earlier eye problem, 792 (9.9%) an ear problem (including 336 with impaired hearing and 482 with non-acute otitis media) and 266 (3.3%) a disorder of balance. No associations were found with glaucoma, cataract, retinal disorders or perforation of the ear drum specifically, but adjusted ORs were moderately elevated for eye and ear problems more generally, and higher where there was a record of blindness or partial sight (OR 1.90, 95% CI 1.05 to 3.44) or non-acute otitis media (OR 2.04, 95% CI 1.64 to 2.54). Risks for non-acute otitis media and for disorders of balance were particularly elevated for consultations in the 12 months preceding injury consultation (OR 2.70, 95% CI 1.58 to 4.62 and 1.77, 95% CI 1.01 to 3.11, respectively).

CONCLUSIONS

Problems of vision, impairments of hearing and disorders of balance all may carry moderately increased risks of occupational injury.

Epilepsy, diabetes mellitus and accidental injury at work

AIMS

To assess the contribution of epilepsy and diabetes to occupational injury.

METHODS

The Clinical Practice Research Datalink logs primary care data for 6% of the British population, coding all consultations and treatments. Using this, we conducted a population-based case-control study, identifying patients aged 16-64 years, who had consulted over two decades for workplace injury, plus matched controls. By conditional logistic regression, we assessed risks for diabetes and epilepsy overall, several diabetic complications and indices of poor control, occurrence of status epilepticus and treatment with hypoglycaemic and anti-epileptic agents.

RESULTS

We identified 1348 injury cases and 6652 matched controls. A total of 160 subjects (2%) had previous epilepsy, including 29 injury cases, whereas 199 (2.5%) had diabetes, including 77 with eye involvement and 52 with a record of poor control. Odds ratios (ORs) for occupational injury were close to unity, both in those with epilepsy (1.07) and diabetes (0.98) and in those prescribed anti-epileptic or hypoglycaemic treatments in the previous year (0.87-1.16). We found no evidence of any injury arising directly from a seizure and no one had consulted about their epilepsy within 100 days before their injury consultation. Two cases and six controls had suffered status epilepticus (OR versus never had epilepsy 1.61). Risks were somewhat higher for certain diabetic complications (OR 1.44), although lower among those with eye involvement (OR 0.70) or poor diabetic control (OR 0.50). No associations were statistically significant.

CONCLUSIONS

No evidence was found that diabetes or epilepsy are important contributors to workplace injury in Britain.

The role of mental health problems and common psychotropic drug treatments in accidental injury at work: a case-control study

OBJECTIVES

Mental illness and psychotropic drugs have been linked with workplace injury, but few studies have measured exposures and outcomes independently or established their relative timings. To address this shortcoming, we conducted a case-control study nested within a database prospectively recording injury consultations, diagnoses and drug prescriptions.

METHODS

The Clinical Practice Research Datalink logs primary care data for 6% of the British population, coding all consultations (by the Read system) and drug prescriptions. We identified 1348 patients aged 16-64 years from this database who had consulted a family doctor or hospital over a 20-year period for workplace injury (cases, 479 diagnostic codes) and 6652 age, sex and practice-matched controls with no such consultation. Groups were compared in terms of consultations for mental health problems (1328 codes) and prescription of psychotropic drugs prior to the case's injury consultation using conditional logistic regression.

RESULTS

In total, 1846 (23%) subjects had at least one psychiatric consultation before the index date and 1682 (21%) had been prescribed a psychotropic drug. The OR for prior mental health consultation was 1.44 (p<0.001) and that for psychotropic drug treatment was 1.57 (p<0.001). Risks were significantly elevated for several subclasses of mental health diagnosis (eg, psychosis, neurosis) and for each of the drug classes analysed. Assuming causal relationships, about 9-10% of all workplace injuries leading to medical consultation were attributable to mental illness or psychotropic medication.

CONCLUSIONS

Mental health problems and psychotropic treatments may account for an important minority of workplace injuries.