‘This … study provides new and powerful … evidence supporting the contention that occupational exposure to metal fumes defined by selected occupations is a potent risk factor for pneumonia … These findings extend previous observations by showing that severe infection, defined by IPD … is an outcome of concern’.
A few months ago, in the official journal of the Faculty of Occupational Medicine of the Royal College of Physicians of London:[i] Occupational & Environmental Medicine, the results of a Swedish study into occupational invasive pneumococcal disease risk were published.[ii]
Pneumococcal disease is an umbrella term to describe pathologies caused by Streptococcus pneumoniae bacteria (pneumococcus). The origin of infection for invasive (as opposed to less serious non-invasive) pneumococcal disease is usually a sterile site, such as blood, cerebrospinal fluid, or joint fluid. Pneumonia, meningitis, septicaemia, bacteraemia, osteomyelitis and septic arthritis are 6 examples of IPD.[iii]
Researchers at the University of Gothenburg remarked that the existing medical literature had observed an increase in risk of pneumonia onset by workplace exposure to metal fumes.
Indeed, Coggon et al (1994) were first to notice an increased risk of fatal lobar pneumonia among English and Welsh male welders, between the ages of 15 and 64 (but no increased mortality risk in over 65s),[iv] to the extent that it was claimed that there were grounds to classify the pneumonia sub-type as an ‘occupational disease’ in welders. Presupposing that metallic components in fumes were responsible for causing injury, the fact that furnacemen, moulders, and coremakers in foundries also demonstrated elevated mortality levels was explicable.
Subsequently, Palmer et al (2003)[v] analysed a sub-sample of the 1994 study’s participants and confirmed, not just that inhalation of metal fumes (most notably ferrous in nature, i.e. iron-based) increases susceptibility to infectious pneumonia (both fatal and non-fatal cases), but also that the effects of such exposure appear to be reversible following cessation of exposure. The same group of researchers went on, in 2009, to state that metal fume exposure is a ‘material cause’ of occupational mortality, deserving ‘far more attention’.[vi]
Ultimately, however, the risk of invasive pneumococcal disease (IPD) more generally, among workers exposed to metal fumes and other dust, vapour and gas types (broadly defined and ‘inorganic dust’), had not yet been characterised.
[Source: Wikipedia – Weldscientist (11 April 2018): ‘GMAW "Mig" Welding on pipe’]
In order to bridge the gap in understanding, a team, led by Professor Kjell Torén, at the University’s School of Public Health and Community Medicine, conducted a population-based case–control study, observing 4,438 cases of IPD in patients aged between 20 and 65, with particular interest in the odds ratios of practising welders, flame-cutters, foundry workers, steel mill workers and blacksmiths developing serious pneumococcal infections (but excluding former metal workers who had ended their employment longer than 1-year before the onset of disease).
What they discovered was that welders were almost 3 times more likely (odds ratio of 2.99) to develop ‘IPD’ than the control group and more than 3 times as likely (odds ratio of 3.28) to develop ‘IPD with pneumonia’.
What is more, occupational exposure to silica dust was associated with a 33% increase in both the risk of ‘IPD’ and the risk of ‘IPD with pneumonia’. This may be indicative of the fact that silica dust is an ‘independent risk factor’ for IPD – a novel implication.
Evidently, the pattern previously documented in British patients with pneumonia (see above) had been successfully replicated in the present study.
Why does exposure of this type cause IPD?
Offering an explanation of the way in which the body may react to the exposure sources studied, it is postulated that:
‘Inhalation of metal fumes, inorganic and silica dust may suppress alveolar macrophages, causing impaired pulmonary clearance of pathogens and impaired host defence in the respiratory tract. It has also been shown that ultrafine particles present in welding fumes increase the adherence of S. pneumoniae to the respiratory epithelium. Iron particulates present in welding and other metal fumes may facilitate infections by acting as a virulence factor for certain siderophilic microorganisms, especially S. pneumoniae’.[vii]
The researchers also concede that it is possible that tobacco smoking was largely responsible for the trend seen, especially as in Sweden, 17% of 50 to 65-year-olds are habitual smokers:[viii]
‘Active current smoking has been associated with an increased risk for IPD, with as high as a fivefold increased risk among current smokers’.[ix]
On the basis that the study’s limitations do not go as far as to invalidate its findings, the Swedish authors recommend the following methods of intervention for affected workers:
- Firstly, to reduce overall workplace exposure to metal fumes, gases and inorganic dusts; and
- Secondly, to settle an historic debate in the UK and mandate pneumococcal vaccinations for the benefit of welders and those in other occupations that involve heavy exposure to metal fumes.[x]
Finally, the authors echo decades-old demands for lobar pneumonia in welders to be classified as an ‘occupational disease’, under the Industrial Injuries Disablement Benefit (IIDB) scheme, but request that this classification is extended to encompass all IPD among welders.
The Industrial Injuries Advisory Council (IIAC) made no recommendations to broaden the list of ‘prescribed diseases’ in its Information Note (dated November 2010).
[ii] Torén K et al., Occupational exposure to dust and to fumes, work as a welder and invasive pneumococcal disease risk. Occupational & Environmental Medicine. 2020 Feb;77(2):57-63. <https://oem.bmj.com/content/oemed/77/2/57.full.pdf> accessed 29 April 2020.
[iii] ‘Pneumococcal infections’ (26 February 2020 NHS Inform) <https://www.nhsinform.scot/illnesses-and-conditions/infections-and-poisoning/pneumococcal-infections> accessed 29 April 2020.
[iv] Coggon D et al., Lobar pneumonia: an occupational disease in welders. Lancet. 1994 Jul 2;344(8914):41-3. https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(94)91056-1/fulltext> accessed 29 April 2020.
[v] Palmer KT et al., Exposure to Metal Fume and Infectious Pneumonia. Am J Epidemiol. 2003 Feb 1;157(3):227-33. <https://academic.oup.com/aje/article-pdf/157/3/227/157681/kwf188.pdf> accessed 29 April 2020.
[vi] Palmer KT et al., Mortality from infectious pneumonia in metal workers: a comparison with deaths from asthma in occupations exposed to respiratory sensitizer. Thorax. 2009 November ; 64(11): 983–986 <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3442248/pdf/ukmss-49437.pdf> accessed 29 April 2020.
[vii] Palmer KT et al., Inflammatory responses to the occupational inhalation of metal fume. Eur Respir J. 2006 Feb;27(2):366-73. <https://erj.ersjournals.com/content/erj/27/2/366.full-text.pdf> accessed 1 May 2020.
Ghio AJ, Particle exposures and infections. Infection. 2014;42:459–67. <https://link.springer.com/article/10.1007/s15010-014-0592-6> accessed 1 May 2020.
Di Benedetto F et al., Physico-chemical Properties of Quartz From Industrial Manufacturing and Its Cytotoxic Effects on Alveolar Macrophages: The Case of Green Sand Mould Casting for Iron Production. J Hazard Matter. 2016 Jul 15;312:18-27.
<https://www.sciencedirect.com/science/article/abs/pii/S030438941630231X?via%3Dihub> accessed 1 May 2020.
Suri R et al., Exposure to Welding Fumes and Lower Airway Infection With Streptococcus Pneumoniae. J Allergy Clin Immunol. 2016 Feb;137(2):527-534.e7. <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4747856/pdf/nihms747548.pdf> accessed 1 May 2020.
[viii] Torén K et al., Vital Capacity and COPD: The Swedish CArdioPulmonary bioImage Study (SCAPIS). Int J Chron Obstruct Pulmon Dis. 2016 May 2;11:927-33. <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4859418/pdf/copd-11-927.pdf> accessed 4 May 2020.
[ix] Nuorti JP et al., Cigarette Smoking and Invasive Pneumococcal Disease. Active Bacterial Core Surveillance Team. N Engl J Med. 2000 Mar 9;342(10):681-9. <https://doi.org/10.1056/nejm200003093421002> accessed 1 May 2020.
Grau I et al., Smoking and Alcohol Abuse Are the Most Preventable Risk Factors for Invasive Pneumonia and Other Pneumococcal Infections. Int J Infect Dis. 2014 Aug;25:59-64. <https://www.ijidonline.com/action/showPdf?pii=S1201-9712%2814%2900027-7> accessed 1 May 2020.
[x] Coggon D et al., Pneumococcal vaccination for welders. Thorax. 2015;70:198-199. <https://thorax.bmj.com/content/thoraxjnl/70/2/198.full.pdf> accessed 1 May 2020.