Sleep-wake patterns and subjective sleep quality of day and night workers: interaction between napping and main sleep episodes.

Five hundred and ninety-three women electronics workers were studied to determine if there was any association between their subjective sleep quality and their sleep patterns. They were 108 day workers, 107 permanent night workers, 216 workers on weekly phase-advance (night/afternoon/morning), and 162 workers on two-weekly phase-delay (morning/afternoon/night) rotating shift schedules. The study was part of a larger survey on night workers involving a self-administered questionnaire. The proportion of nappers was higher in night workers than in day, morning, and afternoon shift workers. Nappers had shorter main sleep, but their total sleep duration was generally the same as that of nonnappers. Compared to nonnappers, a higher proportion of day and morning shift workers who napped did not sleep well. Permanent night workers, with the highest proportion of nappers, had more workers sleeping well than rotating night workers. Subjects who slept well were those with longer total and main sleep and generally started the main sleep earlier. The results indicate a relationship between subjective sleep quality, sleep length, main sleep start, and napping behavior. Whether this relationship is causal is difficult to establish as sleep quality may also reflect the general health status, and this may result in differences in sleep behavior.

Postural stability among manganese exposed workers.

Postural stability was investigated by static posturography in 32 manganese exposed workers with exposure duration of 6.6 (range 1.1-15.7) years and 53 referent subjects. The mean current urine manganese concentration for the exposed was 6.0 micrograms/g creatinine (range 0.6 to 53.3). There was no significant differences between both groups for the postural sway parameters obtained during eyes open condition. However, significant differences were observed for L - length of sway path and Vel - mean velocity of the center of pressure along its path. The Romberg Ratios (the relationship between eyes closed/open conditions) for the exposed's Vel, L, and Ao were also significantly different from the referent. The study showed that manganese exposed workers had significantly poorer postural stability compared to a referent group. We postulate that this could be a subclinical effect of manganese on the basal ganglia (pallidus) resulting in the postural instability when the visual input is cut off. Based on the current urinary manganese levels, we were not able to obtain any significant association with the postural sway parameters.

Neurobehavioral functions among workers exposed to manganese ore.

The Neurobehavioral Core Test Battery of the World Health Organization was performed on 17 baggers (mean age 36.6 years) in a manganese ore milling plant and 17 referents (mean age 35.7 years). The baggers had a mean exposure period of 7.4 (range 1-14) years with a mean blood manganese concentration of 25.3 (range 15-92.5) micrograms.l-1 [0.46 (0.27-1.68) mumol.l-1]. Of the 37 symptoms related to the nervous system, 20 were more frequently reported by the exposed workers. No significant differences were noted between the nerve conduction of the median and ulnar nerves of the dominant forearm of the two groups. The exposed workers had significantly poorer motor speed, visual scanning, visuomotor coordination, visuomotor and response speed, and visuomotor coordination and steadiness. A clinical examination did not reveal any abnormality among the two groups. Hence a neurobehavioral test battery may be a more sensitive method than a clinical examination in detecting early changes in motor function among manganese-exposed workers.

Shiftwork in Singapore.

In 1985, over 94,000 persons were engaged in shiftwork. With the continued emphasis on capital-intensive industries and growing demand for "round-the-clock" services, shiftwork is increasingly becoming an economic necessity in many industries in Singapore. A survey in 1991 confirmed this trend. The study covered 4,996 private sector establishments employing 25 or more paid employees. 34.4% of the establishments had shiftworkers. In terms of employees, 32% or 206,965 employees were working shifts. While the 8-hour shift schedule was still the predominant pattern, there was a ten-fold increase in the number of 12-hour shiftworkers. A trend towards permanent shift schedules was also noted. It was interesting that the proportion of shiftworkers doing nightwork decreased to 36.9% from 45.1% in 1985. The health implications of shiftwork have been widely reported. So far, our own studies indicate no serious long-term health effects among shiftworkers. However, further studies are needed to determine if preventive measures can be taken to minimise the common complaints of sleep problems and tiredness, particularly among rotating shiftworkers.

Sickness absence in private sector establishments in Singapore.

AIM: A study was conducted in June 1995 to determine the current level of sickness absence in Singapore. METHOD: The questionnaire survey was part of a larger labour market survey conducted quarterly by the Ministry of Labour, and covered 3,553 private sector establishments employing 25 or more employees. RESULTS: Overall, 14.4% of the 628,477 employees took sick leave, while the percentage of working days lost due to sick leave, excluding maternity leave, was 1.1%. An average of 3.2 days of medical leave were taken per person per year. Industry specific characteristics seemed to have more influence on sickness absence than establishment size, employee's sex and occupation (viz, professional versus clerical versus production staff), number of hours worked and overtime work. Over 60% of the establishments, particularly larger companies and those in manufacturing, implemented measures to control sickness absence, most commonly counselling, disciplinary procedures and attendance allowance or bonus. Over 13% monitored sickness absence using computerised records. CONCLUSION: Comparing with overseas sickness absence (lost time) rates, the rates observed in this study do not appear high.

Chlamydial infection in female prostitutes in Singapore.

Three studies conducted in 1982, 1985 and 1988 investigated chlamydial infections in female prostitutes. In 1982, 115 prostitutes with culture-positive gonorrhoea were studied; 8% were coinfected with Chlamydia trachomatis. In 1985, 86 female prostitutes and in 1988, 100 female prostitutes attending for routine tests were examined. Chlamydia trachomatis was isolated in 12% and 9% of the cases, respectively. Gonorrhoea was detected in 10% and 11% of the cases. In the 1988 study, one (9%) of the 11 women with gonorrhoea had concomitant chlamydial infection. Syphilis was diagnosed in 3% of the female prostitutes investigated in 1988. Our findings indicate that concomitant chlamydial infection occurs in about 8-9% of female prostitutes with gonorrhoea and that 9-12% of the female prostitutes screened harboured Chlamydia trachomatis in their endocervices. A chlamydial control programme in prostitutes is desirable.

PIP: Studies conducted in 1982, 1985, and 1988 among female prostitutes in Singapore documented the need for a chlamydial control program in this population. In the 1982 study, which included 115 prostitutes infected with gonorrhea, Chlamydia trachomatis was recovered from 8%. In 1985 and 1988, the prevalence of endocervical chlamydia infection in prostitutes presenting for routine testing was 12% and 9%, respectively. The prevalence of gonorrhea in 1985 and 1988 was 10% and 11%, respectively. In the 1988 study, 1 of the 11 prostitutes with gonorrhea also harbored chlamydia. The prevalence of syphilis, ascertained only in the 1988 study, was 3%. These findings suggest that 8-9% of prostitutes with gonorrhea are co-infected with chlamydia. At present, prostitutes in Singapore are screened only for gonorrhea and syphilis. The high rate of C trachomatis infection recorded in this study indicates that chlamydia infection--on the increase in the West--should be added to this list. In addition, health education efforts are needed to stress the need for additional anti-chlamydial treatment. Currently utilized regimens for the treatment of gonorrhea are ineffective against C trachomatis.

Cadmium hazard in silver brazing.

This study evaluates the usage of cadmium-containing silver brazing alloys in Singapore and the potential cadmium hazard from its use. Of the 137 factories which responded to the survey questionnaire, only 28 (20.4%) carried out brazing. Of these, only 7 factories used cadmium-containing filler alloys. One hundred and six out of 123 workers from one of these factories had cadmium-in-blood concentrations exceeding 10 mcg/l. Thirty-one (29.2%) of the workers with excessive cadmium absorption had urinary beta-2 microglobulin levels exceeding 28 mcg/g creat. Workers in the other factories who were intermittently exposed had cadmium-in-blood concentrations of 10 mcg/l and below.

Five cases of arsine poisoning.

Arsine is one of the most potent haemolytic agents found in industry. Four workers presented with abdominal pain, jaundice and passing tea-coloured urine. A fifth worker also passed dark urine but had no other symptoms. Investigation revealed that all five workers were from a tin smelting plant where they were involved in mixing tin ore with dross. They were exposed to arsine gas after mixing a particularly large quantity of dross with tin ore which was wet because of rain. Three of the cases developed renal impairment and also a mild sensory neuropathy. All survived with proper management in hospital which included exchange blood transfusions, and peritoneal dialysis where indicated. Prevention of such poisoning includes keeping dross away from all moisture, good ventilation in work areas, and adding dross directly to the furnace.

Efficacies of a barrier cream and an afterwork emollient cream against cutting fluid dermatitis in metalworkers: a prospective study.

We compared the point prevalence of cutting fluid dermatitis and transepidermal water vapour loss (TEWL) changes in groups of new machinists who (a) used a barrier cream; (b) used an afterwork emollient cream; and (c) did not use any cream (controls) over a 6-month period. All machinists handled cutting fluid (neat mineral oil) during their work. There was no significant difference in the prevalence of cutting fluid dermatitis in the 3 groups throughout the study period. The prevalence of cutting fluid dermatitis in all groups increased rapidly during the first 6 weeks and thereafter remained steady throughout the remainder of the study period. The prevalence of cutting fluid dermatitis was slightly lower in machinists using afterwork emollient cream compared to those using barrier cream and controls (not significant). The differences in the mean TEWL changes during the study period among the 3 groups were also not statistically significant. The mean TEWL values in the 3 groups increased rapidly during the first 6 weeks of exposure to cutting fluids and thereafter remained fairly constant throughout the remainder of the study period. Barrier cream and afterwork emollient cream did not appear to have any significant effect against either cutting fluid dermatitis or TEWL changes in machinists exposed to cutting fluid. However, afterwork emollient cream appeared clinically to help reduce the prevalence of cutting fluid irritation.

The incidence of cutting fluid dermatitis among metalworkers in a metal fabrication factory: a prospective study.

We compared the incidence of occupational dermatitis and transepidermal water vapour loss (TEWL) changes from cutting fluids (neat mineral oils) in 24 new machinists with 27 armed forces paramedics (controls) over a 6-month period. The cumulative incidence of occupational dermatitis in positive controls increased from 38% at week 3 to 77% at week 6. It then decreased to 50% at week 9 and thereafter remained constant at about 50% throughout the remaining study period. 2 workers sought medical treatment for their dermatitis. Only 1 worker had a job transfer because of his dermatitis. None of the paramedics developed dermatitis during the study period. The mean basal TEWL values on the hands of machinists and controls were 17.6 and 14.5 g/m2/h (n.s.) respectively. The mean TEWL values of machinists increased to 22 g/m2/h by week 3 and then remained fairly constant throughout the remaining study period. The mean TEWL of negative controls remained fairly constant (at about 14 g/m2/h) from the beginning to the end of the study period. The mean TEWL value of machinists was significantly higher than that of negative controls throughout the study period. There was no significant difference in the prevalence of cutting fluid dermatitis between machinists with high basal TEWL values (> or = 17 g/m2/h) and those with low basal TEWL values (< 17 g/m2/h).

Change in cement manufacturing process, a cause for decline in chromate allergy?

Hexavalent chromate in cement is the commonest cause of allergic contact dermatitis, especially among construction workers. Over the past decades, there has been a general decline in the prevalence of chromate allergy among construction workers. We suspect that a change in the constituents of cement, resulting in the lowering of hexavalent chromate, contributed to the decline. Slag (free from hexavalent chromate) from the iron-quenched, blast furnace process has been used as a substitute for clinker (which contains high hexavalent chromate) in manufacturing cement. As a result, the slag has diluted the hexavalent chromate content of cement. Our analytical study showed that slag is free from hexavalent chromate and that the hexavalent chromate of clinker ranged from 6-17 micrograms/g. Substituting slag for clinker resulted in dilution of hexavalent chromate in the cement. The hexavalent chromate content of cement declines proportionately with increasing proportion of slag, e.g., a cement containing 5% slag has a total hexavalent chromate concentration of 17.5 micrograms/g, whereas increasing the proportion of slag to 60% reduced the hexavalent chromate content to 7.1 micrograms/gm in the same cement.

Cobalt and nickel content of Asian cements.

The total cobalt and nickel concentration of 11 brands of Asian cement ranged from 8.1 to 14.2 micrograms/g and 14.9 to 28.5 micrograms/g, respectively. These metals exist mainly as insoluble salts; the water-soluble concentration of cobalt and nickel in the cements ranged from 0.39 to 0.65 micrograms/g and from 0-1.2 micrograms/g, respectively. 1.5% (4/272) of construction workers in a prefabrication construction factory had cobalt sensitivity. All had allergic contact dermatitis from chromate in cement. No worker had isolated cobalt sensitivity and cement dermatitis. It appeared that sensitization to cobalt in cement occurs only secondarily to an existing cement dermatitis. 1.8% (5/272) workers had nickel sensitivity: 2 with allergic contact dermatitis to nickel in their watches, 2 were asymptomatic and 1 had allergic contact dermatitis to chromate and cobalt in cement. The low prevalence of cobalt and nickel sensitivity from cement was probably related to the low concentration of soluble cobalt and nickel salts in the cement. However, these insoluble salts can form soluble complexes with body fluids on eczematous skin and sensitize the skin.

Occupational dermatitis in a prefabrication construction factory.

In a field study of occupational dermatoses in a prefabrication construction factory, 272 workers were interviewed, examined and patch tested to chromate, cobalt, nickel, rubber mixes, epoxy resin, melamine formaldehyde and conplasts. The prevalence of occupational dermatitis was 14% (38/272); 57% (22/38) were irritant dermatitis from cement; 39.5% (15/38) were allergic contact dermatitis from cement (2 with concomitant rubber glove allergy); and 2.5% (1/38) were allergic to rubber chemicals in gloves. The overall prevalence of chromate sensitivity was 8.5% (23/272), with the highest rate from the concreting bays of the factory. The rate was unrelated to the duration of workers' engagement in construction work. 34.8% (8/23) had asymptomatic chromate allergy. The prevalence of cobalt reactions was 17.4% (4/23) and all were associated with chromate allergy.

Study on the health of female electronics workers on 12 hour shifts.

Health complaints, blood pressure, sleep and sickness absence experience were studied in 308 female electronics workers employed for at least one year on 12 h shifts--253 on permanent and 55 on rotating schedules. Seventy-five 8 h day workers acted as controls. There were no significant differences in symptom prevalence between the controls and 12 h shift workers, except for complaints of tiredness, with a higher proportion of the rotating shift group also having headaches. No significant differences in prevalence of hypertension were noted. Although subjects on the night shift had shorter sleep than controls and 12h day workers, only the group on rotating schedule had a higher proportion of workers who did not sleep well compared to the controls. Sickness absence was not increased in the 12 h shift groups when compared to the controls. The results indicate no serious health problems among workers on 12 h shift for over a year.

Persistent liver dysfunction among workers at a vinyl chloride monomer polymerization plant.

Thirteen workers with persistent abnormalities in one or more liver function tests (LFT) at a vinyl chloride monomer (VCM) polymerization plant were investigated. Twelve workers were found to have VCM-induced liver dysfunction based on circumstantial evidence. They were employed between 1971 and 1982 when the VCM levels ranged from 1 to 21 p.p.m. After 1982 when the environmental VCM levels were controlled to below 1 p.p.m., no cases of VCM-induced liver dysfunction were detected. In most cases, glutamic pyruvic transaminase was the earliest parameter to be raised. The second most common parameter is serum gamma glutamyl transpeptidase. The latent period ranged from 1 to 13 years. An improvement in their LFT results was shown by 83.3 per cent of workers within 6 months to 2 years after removal from further VCM exposure. For workers who returned to VCM work, their LFT became abnormal again. Liver scans showed hepato and/or splenomegaly in most cases. Liver biopsies on 9 workers were reported as 'non-specific fatty changes' of varying degrees. These observations highlight the need for continual vigilance with environmental monitoring and medical surveillance of VCM-exposed workers.

Chromate allergy: total chromium and hexavalent chromate in the air.

This is a study on atmospheric concentration of total chromium and hexavalent chromate and its role in chromate sensitivity. Air concentration of total chromium and hexavalent chromate in a construction factory, a busy city area, a suburban area, a residential area, and a heavy industrial area were measured by air sampling pumps. Hexavalent chromate was not detected in any sampled areas. Two (concreting areas) of 8 locations in the construction factory had total chromium of 0.2 and 2.3 micrograms/m3 in the atmosphere. It appeared that the atmospheric concentration of total chromium and hexavalent chromate was negligible. These findings indicate that unexplained chromate sensitivity, as so often seen in patients attending a contact dermatitis clinic, is not attributable to exposure to hexavalent chromate in the air.

Occupational dermatosis among sanders in the furniture industry.

The prevalence of occupational skin disease was found to be 3.8% in a study of 479 sanders in the furniture-making industry in Singapore. 17 species of wood imported from South East Asia were used. The most common dermatoses from wood dust were pruritus (1.6%), irritant contact dermatitis (1.6%) and xerosis (1.4%). 2 sanders had miliaria. None had allergic contact dermatitis from wood dust. The arms and trunk were the most common site for pruritus and dermatitis from wood dust. It appeared that the woods commonly used in the furniture making industry are weak sensitizers. Appropriate preventive measures against irritant dermatitis such as dust control, protective clothing, and good personal hygiene should be adequate to prevent occupational dermatoses among the sanders.