Shield Report 2010

Shield Report 2010

C Burge, VC Moore, AS Robertson, AD Vellore, E McGrath 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. The rate of reporting increased sharply in 2004, mainly due to a major outbreak, but since then we have seen a steady decrease in reports. We think this is mainly due to a reduction in the number of doctors / clinics at the Birmingham Chest Clinic.

The most common causes in 2010 were Isocyanates (11 cases), followed by Cleaning agents (7 cases).

Nearly all cases reported in 2010 were by the Birmingham Chest Clinic. We hope to increase the number notified by others this year by using the MTS website to contact notifiers. The most common method for the diagnosis of occupational asthma still remains a history of improvement of symptoms during holidays or periods off work.

The method of reporting to the Shield scheme has now changed and is done via the new version of the Oasys program that works through the internet. For those that use serial peak flows as a method of diagnosis this will greatly improve the ease of reporting. The data collected is all anonymous and so there are some changes in the data that we record, although it is largely similar.


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 (we don't collect this anymore), and 3) to audit diagnostic methods and objectives.

The last report on Shield's progress was written in 2009 and summarised the information gained in that year, to that of previous years, 2008 and 2007. This report aims to update the participants of Shield by summarising the trends found in 2010 compared to those found in 2009 and 2008.

Outbreak of the year

Hardly an outbreak but two workers were seen from the same histopathology laboratory with occupational asthma from formaldehyde. The laboratory was unusual in that it specialised in amputated limbs which are obviously very large compared with normal histopathology specimens making formaldehyde exposure more difficult to control. The widespread use of cut-up tables with down draft ventilation has greatly reduced formaldehyde exposures in histopathology departments, but large objects (or cut-up slabs) reduce their efficiency. Some believe that formaldehyde is not a cause of occupational asthma. Since 1989 there are 33 notifications of formaldehyde asthma to Shield, including 4 from histopathology laboratories, 10 from foundries using phenol formaldehyde hot box systems for making cores, 3 from injection moulders of formaldehyde-based resins and 4 from chemical works manufacturing formaldehyde.

Agent Awareness

A 48 year old worker developed cough, sputum and wheeze 11 years after starting work as a brick maker where pond water was used to wet the sand and clay before baking and sprayed to reduce dust in hot weather. Serial PEF records showed intermittent occupational asthma. We wondered whether he had low-dose irritant induced asthma similar to a bricklaying lecturer who had a positive challenge to lime dust. The brick maker had a negative challenge to lime dust but a positive challenge to nebulised pond water. Microbial contaminated water is a well recognised cause of occupational asthma, humidifier fever and allergic alveolitis from air humidification systems.

Shield Data

Number of Cases

The number of cases of occupational asthma reported to the Shield scheme is 29 so far. 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 2010

Personal details

In the year of 2010, 29 new cases have been reported to the scheme so far. As the data is anonymous we can no longer report the percentage of men and women. 21 (72%) of the new cases had no pre-existing asthma, 12 (41%) were non atopic and 9 (29%) had never smoked.

Reporting Hospital and Physician

The data is now collected anonymously so we are no longer recording the reporting hospital and physician.

Suspected agents at work

In 2010 the most commonly reported agent that workers were exposed to was Isocyanates (11 cases), followed by Cleaning agents. (7 cases). There were 4 cases exposed to preservatives, although this is a constituent of many cleaning agents and so there is some overlap, with some patients being counted in both categories.  The 2 most common in 2009 were cleaning agents and metal working fluids (7 and 4 cases respectively). Isocyanates were also the most common in 2008. 461 cases of isocyanate suspected asthma have now been reported to the scheme, the first case being in 1978. Metal exposed cases are low and stable with only 4 notifications being made in 2009.

The top reported agents in 2010 were as follows.

Agent 2010  2009 
Isocyanates  11  3 10
Cleaning agents  7  7  2
Metals  4
Metal Working Fluid  3  4  2
Colophony  3

Formaldehyde  3

Adhesives  1  2  
Latex  2  1  
Wood dusts  2  3 2

Employers and Jobs

The employer for a patient is encrypted when sent to the Oasys Internet Database for confidentiality reasons so it is no longer possible to report this. The jobs are still reported but we have found that job descriptions are very specific and there is rarely more than one patient for each type of job so we have stopped reporting these too.

Methods used for diagnosis

The methods used for 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, 6) Methacholine away from work and 7) Specific bronchial provocation tests. 22 cases were documented as improving off work and on holidays. There were 2 specific challenges performed on patients diagnosed in 2010. 

Method % 2010  % 2009 
% 2008
Improving on holidays  76  85 92
Improving off work  76  82 89
Serial peak flow  100  82 81
Specific IgE  28  41 53
Methacholine at work  76  59 58
Methacholine away from work  34  18 31
Specific Bronchial Challenges 
(positive challenges)
 2  10 (1) 8 (2)

Proposed method of asthma

We no longer record the proposed mechanism of asthma.

Subsequent History

We no longer record the subsequent history.

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. 3 cases have become gold standards in 2010 so far. The database does not automatically record gold standard cases due to a fourfold change in bronchial reactivity any more, as there are a lot of different methods of measuring bronchial reactivity that all have different units.

BTS Audit Guidelines

The audit recommendations from the BTS Standards of care for occupational asthma (Fishwick D et al. Standards of care for occupational asthma, Thorax, 2008; 63 : 240-250) are now collected through Oasys. This is the first year that we have recorded adherence with the BTS Audit guidelines. The figures below show the percentage done by visit 2 or before. Specific IgE tests are not available for all agents, so this number is artificially low. The data for the audit was not collected until mid way through 2010 and the denominator is for all reports in 2010. The numbers in brackets show the percentages of patients where any of the audit data was recorded.

  % 2010 % 2009  % 2008 
Specific IgE   28 (89)    
Occupational History  48 (93)    
FEV1 / FVC   52 (100)    
Serial Peak Flows  48 (100)    
Employment Advice  45 (87)    
Compensation Advice  34 (91)    

Future Developments

The new version of Oasys is working well and we are now using it to collect data. We are separating out the Shield data into this report. Data from all people using Oasys will now go into the Oasys Usage report, which will have global scope. We hope to colloborate with other surveillance schemes 


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. 


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