Oasys and occupational asthma banner logo

Shield Report 2005; A surveillance scheme of occupational asthma in the Midlands

Shield Report 2005; A surveillance scheme of occupational asthma in the Midlands

V Moore, CBSG Burge, AS Robertson, MS Jaakkola, AD Vellore and PS Burge. Occupational Lung Disease Unit, Heartlands Hospital, Bordesley Green East, Birmingham B9 5SS

SHIELD is the Midland Thoracic Society’s Surveillance Scheme for Occupational Asthma for the West Midlands. The scheme, which was set up in January 1989, was established to study the general and specific incidence of occupational asthma within the West Midlands region and Metropolitan County. There were problems with the parent MTS rare disease reporting scheme in 2003 due to data protection issues which has limited reports from outside the Birmingham Chest Clinic. Despite this the rate of reporting has shown little change over the last few years and increased sharply in 2004, mainly due to a major outbreak, but has returned to normal levels again this year. Seventy-eight reports have been received so far for 2005. The data protection issues are now being resolved and it is hoped that reporting from other hospitals will be implemented this year (2006).

The most common cause in 2005 was Metal Working Fluid (37%) which was all due to the outbreak from 2004. Isocyanates and Chrome came second (14%) showing a significant decrease in the former compared to previous years. The high level of chrome notifications are mostly due to an outbreak of occupational asthma in a foundry where chrome fumes from stainless steel burning was the most likely cause in 2002, and more of these are still being seen. Latex has continued to decline, both in percentage terms and numbers, suggesting that substitution of latex gloves is continuing.

Ninety seven percent of cases reported in 2005 were by the Birmingham Chest Clinic and 3% by others. We hope to increase the number notified by others this year now that data protection issues have been resolved. The most common method for the diagnosis of occupational asthma still remains a history of improvement of symptoms during holidays or periods off work. Some form of objective confirmation was sought in 95% of patients.

We still have plans for web based reporting, but there are higher priorities on the agenda and the plans remain on the shelf for the time being.


Shield is a joint project between the West Midlands branch of the Society of Occupational Medicine and the Midland Thoracic Society. The scheme, which was set up in January 1989, was established to meet three main objectives. 1) To study the general and specific incidence of occupational asthma within a defined geographic area, 2) To determine proposed mechanisms of asthma, and 3) to audit diagnostic methods and objectives. Chest physicians and members of the West Midlands Group of the Society of Occupational Medicine implemented the scheme, by reporting each new case using a questionnaire format. The questionnaire covers confidential personal information on the patient, details of the diagnosis, information about their occupational history, and the outcome after diagnosis.

The last report on Shields progress was written in 2004 and summarised the information gained in that year, to that of previous years, 2003 and 2002. This report aims to update the participants of Shield by summarising the trends found in 2005 compared to those found in 2004 and 2003.

Outbreak of the year

This year we have discovered an outbreak of occupational asthma as well as other work related symptoms in a school for children with special needs. We have seen 8 workers this year and are likely to see more throughout 2006. The school itself employs around 110 workers. The cause of this outbreak is as yet unknown, but possibilities include flooring adhesive and cleaning products.

Agent Awareness

The main agent reported to the scheme in 2004 and 2005 was metal working fluid. This is mainly found in industries that grind and drill metal components. The West Midlands is an area of major metal working and metal-working fluids have been a regular cause of occupational asthma since Shield began. In the past most cases have been due to inhalation of used oils, where microbial contamination is the most likely cause. In one plant cobalt (from stellite welding) dissolved in the coolant is the most common cause. Occasional cases are due to constituents of the unused oil, particularly colophony or tall oil products. We have also had a previous outbreak of alveolitis and asthma due to a contaminated water-based humidifier in a printing works, controlled by replacement with a steam humidifier (Thorax 1985;40: 248-254).

Shield Data

Number of Cases

The number of cases of occupational asthma reported to the Shield scheme is 78 so far. When the SHIELD report for 2004 was written, there were 110 cases notified, but now this figure is up to 122. It is difficult to compare notification for each year properly, as the last few years are likely to change, therefore the graph below is only as a guideline.

Figure 1 Number of cases diagnosed with occupational asthma between the years of 1980 and 2004 (cases pre 1989 retrospective reports) Figure 1: Number of cases diagnosed with occupational asthma between the years of 1980 and 2005

Personal details

In the year of 2005, 78 new cases have been reported to the scheme so far. There were 59 males (76 %), and 19 females (24 %). 63 (81%) of the new cases had no pre-existing asthma, and 36 (46%) had never smoked.

Reporting Hospital and Physician

The Shield scheme is confined to the West midlands Region and the West Midlands Metropolitan County. In this region there are many chest physicians, hospitals, clinics and other organisations, which are known to the Shield scheme. However, many of these have not been asked to report over the last year due to the data protection issues. Therefore, in 2005, 76 (97 %) of the cases reported to Shield were through the Birmingham Chest Clinic, and 2 (3 %) through other organisations. We are hoping that there will be more cases reported from other institutions in the coming year.

Suspected agents at work

In 2005 the reported agents that the workers were exposed to is dominated by the outbreak and is metal working fluid. The most common in 2004 was also metal working fluid for the same reason, but in previous years (except 1997) the most common was isocyanates, but reports have tailed off this year. 428 cases of isocyanate suspected asthma have now been reported to the scheme, the first case being in 1978. 25 cases of isocyanate asthma were diagnosed in 2004 and 23 cases in 2003. Latex cases are continuing to decrease and in the last 2 years only 3 notifications have been made. Chrome cases continue to be high and are influenced by the 2002 / 2003 foundry outbreak, from which we are still seeing patients.

The top five agents reported in 2005 were;

  1. Metal Working Fluid 37.2% 29 cases
  2. Chrome 14.1% 11 cases
  3. Isocyanates 14.1% 11 cases
  4. Adhesives 7.7% 6 cases
  5. Biocides/Cleaning agents 6.4% 5 cases

Figure 2 Comparison of the percentage of patients exposed to the top ten agents in 2005 to those exposed in 2004 and 2003.Figure 2.	Comparison of the percentage of patients exposed to the top ten agents in 2005 to those exposed in 2004 and 2003.

Employers and Jobs

There were 43 different employers reported to the scheme in 2005. 26 of these were new to the scheme. The major outbreak for 2005 currently accounts for 28% of all reports in 2005.

Around 58 different jobs were reported in 2005, although it would be possible to group some of the specific jobs into broader categories. The most common job was maintenance work at 10% of all notifications in 2005.

Table 1 A list of the most common agents reported in 2005 with the corresponding jobs
Agent Exposed Job
Metal Working Fluid Maintenance engineer, CNC operator, assembler, FLT driver, welder, grinder, setter, labourer
Isocyanates Assembler, solderer, arc-air gouger, studio engineer, workshop foreman
Chrome Arc air gouger, plater, CNC operator, yardman, fettler, grinder, foreman
Adhesives Assembler, Science Teacher, Learning support officer, team leader, gluer
Biocides/ cleaning agents Learning support officer, office administrator, edoscopy nurse, machine operator, caretaker
Flour Baker, crumpet maker, driver
Wood dusts Cabinet maker, FLT driver, carpenter, teacher, team leader
Welding fume Welder, general machinist

Methods used for diagnosis

The methods used for the diagnosis that are documented on the shield form are; 1) Improvement on holiday, 2) Improvement off work, 3) Serial peak flow charts, 4) Specific IgE, 5) Methacholine at work, and 6) Methacholine away from work and 7) Specific bronchial provocation tests. 95 cases were documented as improving off work and on holidays. Of these, 86 cases had at least one other investigation. The most common investigation was serial peak flow charts (86 cases) followed by specific IgE (73 cases). There were 10 specific challenges performed on patients diagnosed in 2005. In 2004, there were 20 challenges performed.

Table 2 Percentage use of each method of diagnosing occupational asthma in 2005, 2004 and 2003.
Method % 2005 % 2004 % 2003
Improving on holidays 86 92 95
Improving off work 91 87 91
Serial peak flow 86 78 84
Specific IgE 60 66 51
Methacholine at work 50 53 50
Methacholine away from work 26 18 34
Specific Bronchial Challenge 10 20 14

Proposed method of asthma

Figure 4 shows the proposed mechanism of asthma in patients with diagnosed occupational asthma in 2005, 2004 and 2003. In 2005 the most commonly reported mechanisms of asthma were allergic (41 %) and unknown (49%). In 2003 an allergic and unknown mechanisms were also reported in most cases (46% and 45% respectively). The percentage of ‘no answer’ has remained similar in the last 3 years at an average of 8%. The other mechanisms (irritant and direct pharmacological effect) still remain very low in the percentage of proposed mechanisms.

Figure 3Proposed mechanisms of asthma in 2005, 2004 and 2003 Figure 3: Proposed mechanisms of asthma in 2005, 2004 and 2003

Subsequent History

The subsequent history of the patients diagnosed with occupational asthma in 2005 is broadly similar to that of 2003 and 2002, except there are less that have had the agent replaced at work. There are many patient’s still exposed but the number off sick is continuing to go down. Moving within the workplace and replacing the agent are popular options and respiratory protection was seen extensively in 2004. The outbreak in 2004 had a large influence on these figures, where the suspected agent was replaced. This is probably less likely to happen where only one or two workers are having problems in a workplace. Relocation at work probably remains the most effective solution in most cases. The recorded subsequent history of the patient is taken at diagnosis and is subject to change so these figures will change with time.

Figure 4Subsequent history of patients diagnosed of occ. asthma in 2005, 2004 and 2003 Figure 4: Subsequent history of patients diagnosed of occ. asthma in 2005, 2004 and 2003

Gold Standards

A gold standard occupational asthma case is defined by either; 1) Bronchial challenge test, 2) A four fold change in their bronchial reactivity with a good history, or 3) Positive IgE with a good history, and all of these can be accompanied by a good quality PEF record. 5.1% of cases have become gold standards in 2005 so far. This is lower than previous years but will improve as we receive more results. We were unable to conduct bronchial challenges at the beginning of 2005 which makes numbers slightly lower.

Future Developments

The problems with the Shield scheme are lack of reporting, a need for constant updating and a lack of resources. We have solved the data protection issues and will start to request notifications from other institutions this year. We would like to add web based reporting to improve notification and updating but this is on hold for the time being due to time constraints. There are organisational and technical changes to be made to improve accuracy and to help keep data up to date. We have plans for these but there is no date set for implementation as yet.


Occupational asthma remains a serious disease causing much morbidity, and is potentially preventable. The Health and Safety Executive are currently emphasising the need to control occupational asthma. Workers involved in car manufacture amongst others are a high risk group for the development of occupational asthma.


Please sign in or register to add your thoughts.

Oasys and occupational asthma smoke logo