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Shield Report 2002; A Surveillance Scheme of Occupational Asthma in the Midlands

Shield Report 2002; A Surveillance Scheme of Occupational Asthma in the Midlands

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 have been problems with the parent MTS rare disease reporting scheme this year 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. Seventy seven reports have been received so far for 2002.

The most common cause was isocyanates (24.6%) and has been for the last 11 years. Reports of latex allergy were up again this year after some years with decreasing reports, suggesting that further substitution of latex gloves is required. There has been an outbreak of occupational asthma in a foundry where chrome fumes from stainless steel burning is the most likely cause.

Eighty seven percent of cases reported in 2002 were by the Birmingham Chest Clinic and 13% by others, whereas in 2001, 33% of cases were being reported by other organisations. 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 made in 87% of patients.

The report form now has a place for worker consent for the data to be included on the Shield database. We hope to introduce web-based reporting and feedback this year.


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 2001 and summarised the information gained in that year, to that of previous years, 2000 and 1999. This report aims to update the participants of Shield by summarising the trends found in 2002 compared to those found in 2001 and 2000.

Outbreak of the year

This year a foundry making large castings predominantly from stainless steel has produced the most reports. There are two possible causes, isocyanates from the cores (a regular but not very common problem in foundries) and chrome. Several of the affected workers are separated from the core making and casting areas, and chrome fumes generated during powder burning, arc air gouging and welding are the most likely cause. Chrome fumes have been a regular cause of reports to Shield, mostly from electroplating shops. It is likely that the higher than usual level of chrome fumes accounts for this outbreak.

Agent Awareness

Most people would think that those reported as having occupational asthma to cleaning agents must be employed as a cleaner. This is not the case however. This year we have had a record number of cases reported to have problems with cleaning agents, but who are only incidentally exposed as teachers, office workers, and nurses. Remember - every wipeable surface and floor is cleaned with some sort of fluid, and many of them contain biocides to which staff can become sensitized.

Shield Data

Number of cases

The number of cases of occupational asthma reported to the Shield scheme is 77 so far. When the SHIELD report for 2001 was written, there were 72 cases notified, but now this figure is up to 81, and is still rising. 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. The diamond shaped point is an estimate of how many notifications of occupational asthma there will be by 2004.

Figure 1 Number of cases diagnosed with occupational asthma between the years of 1980 and 2002.

Figure 1: Number of cases diagnosed with occupational asthma between the years of 1980 and 2002.


Personal details

In the year of 2002, 77 new cases have been reported to the scheme so far. There were 48 males (62 %), and 29 females (38 %). 58 (75%) of the new cases had no pre-existing asthma, and 31 (40 %) 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. In 2002, 67 (87 %) of the cases reported to Shield were through the Birmingham Chest Clinic, and 10 (13 %) through other organisations. The percentage of cases being reported by the BCC has fallen over the last 3 years, from 77.5% in 2000 to 67% in 2001, but has now increased again. The main "other" contributor is City Hospital, Birmingham (9% in 2002 and 22% in 2001).

Suspected agents at work

In 2002 the reported agents that the workers were exposed to had varied from the previous years. The most common in 2002 and previous years (except 1997) was isocyanates. 341 cases of isocyanate suspected asthma have been reported to the scheme, the first case being in 1978. 19 cases of isocyanate asthma were diagnosed in 2002 and 24 cases in 2001.

The top ten primary agents reported in 2002 were;

  1. Isocyanates (25%)
  2. Chrome (12%)
  3. Cleaning Agents (12%)
  4. Latex (12%)
  5. Glues (10%)
  6. Biocides including glutaraldehyde (8%)
  7. Coolant oils (8%)
  8. Metals (excluding Chrome) (6.5%)
  9. Flour (5%)
  10. Solder/colophony (3.9%)

Most of these agents were in the top ten of 2000, however, cleaning agents and latex notifications have increased in number this year, in that the former did not appear in the top ten in 2001 and the latter has increased from 7% to 11.7%. Metals also featured higher individually in 2001 (except chrome).

Figure 2 Comparison of the percentage of patients exposed to the top ten agents in 2002 to those exposed in 2001 and 2000.

Figure 2: Comparison of the percentage of patients exposed to the top ten agents in 2002 to those exposed in 2001 and 2000.

Employers and Jobs

There were 62 different employers reported to the scheme in 2002. Around half of these were new to the scheme. The major outbreak for 2002 was at a foundry making stainless steel and was due to either chrome or isocyanates. This particular outbreak currently accounts for 11.7% of all reports in 2002.

55 different jobs were reported in 2002. The most common job was nursing at 10.4% of all notifications in 2002.

Table 1 A list of the most common agents reported in 2002 with the corresponding jobs
Agent Exposed Job
Biocides Nurse, radiographer
Chrome Welder, fettler, powder burner, and maintenance engineer
Cleaning Agents Cleaner, nurse, teacher
Colophony Solderer
Flour Baker, bakery manager, kiev maker
Glues Injection moulder, gluer and assembler, printer
Isocyanates Moulder, assembler, foam injector, vacuum former, process operator, engineer, coremaker, lab technician, panel beater
Latex Nurse, healthcare assistant, midwife, dental clerk
Metals (excl. Chrome) Welder, grinder, polisher, brazer
Oils CNC operator

Methods used for diagnosis

The methods used for the diagnosis of occupational asthma vary between each hospital and each physician. The methods 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. 66 cases were documented as improving off work and on holidays. Of these, 55 cases had at least one other investigation. The most common investigation was serial peak flow charts (49 cases) followed by IgE (35 cases). There were 19 specific challenges in total in 2002 performed on 13 different patients, and of these approximately half were done within one year of diagnosis. In 2001, there were 18 challenges performed on 16 different patients, with 12 of these being within one year of diagnosis.

Table 2 Percentage use of each method of diagnosing occupational asthma in 2002, 2001 and 2000.
Method % 2002 % 2001 % 2000
Improving on holidays 92.2 97.6 91.0
Improving off work 88.3 97.6 92.0
Serial peak flow 63.6 74.1 71.0
Specific IgE 45.5 45.1 39.0
Methacholine at work 40.3 23.2 25.0
Methacholine away from work 26.0 34.1 27.0
Specific Bronchial Challenge 2.6 (so far) 11.1 15.0

Proposed method of asthma

Figure 4 shows the proposed mechanism of asthma in-patients with diagnosed occupational asthma in 2002, 2001 and 2000. In 2002 the most commonly reported mechanism of asthma was allergic 31 (40.3 %). In 2001 an allergic mechanism was also reported in most cases, however the overall percentage was more (47%). The percentage of the cases where the mechanism is not known is slightly more in 2002 (39%) compared to the previous year (33 %), but the percentage of 'no answer' has decreased in 2002 compared to last year. The other mechanisms (irritant and direct pharmacological effect) still remain low in the percentage of proposed mechanisms.

Figure 3 Proposed mechanisms of asthma in 2002, 2001 and 2000.

Figure 3: Proposed mechanisms of asthma in 2002, 2001 and 2000.

Subsequent History

The subsequent history of the patients diagnosed with occupational asthma in 2002 is very similar to that of 2001 and 2000. A similar significant percentage are still exposed at work, but less are off sick than in 2001. Relocation in the work place has increased and still remains the most popular solution. The percentage of 'no answer' has decreased further from 2000. The recorded subsequent history of the patient is taken at diagnoses and may be changed as investigations occur, this means that the form should be updated and the true outcome for the patients diagnosed with occupational asthma in 2002 will not be seen until possibly the end of 2003.

Figure 4 Subsequent history of patients diagnosed of occupational asthma in 2002, 2001 and 2000.

Figure 4: Subsequent history of patients diagnosed of occupational asthma in 2002, 2001 and 2000

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. 13% of cases have become gold standards in 2002 so far, which is similar to the amount in 2001 at this time, but this has now risen to 17%. As gold standard notation is dependent upon the results of investigations it is likely that the number for 2002 will rise over the next year.

Future Developments

The problems with the Shield scheme are still lack of reporting and a need for constant updating. Consent is an issue and we have now changed our form to include this, but a patient information leaflet needs to be written also. The number of 'no answers' to questions implies that the results of further investigations are not being reported. To try and solve the above problems we have started to send a report of all the details back to the referring consultant. This enables the physician to complete the form as and when the investigations are carried out, and to send the form back when more information is added. Using this method it will be clear in the notes if the patient has been reported and at what stage the investigations are at whilst maintaining an up to date database. We hope to add email reporting and feedback this year.


Occupational asthma remains a serious disease causing much morbidity, and is potentially preventable. The Health and Safety Executive are currently emphasising the need to sort out occupational asthma. Healthcare personnel amongst others are a high risk group for the development of occupational asthma.


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