Previous research suggests that occupational exposure to inorganic dust, fumes and fumes may lead to an increased risk of pneumococcal pneumonia, particularly in the year following exposure. It is unclear to what extent the total cumulative exposure to dust and vapor has an influence.
Streptococcus pneumoniae (S. pneumoniae) causes various ailments, including pneumonia. in Europe S. pneumoniae therefore one of the most common causes of pneumonia. Sometimes this is accompanied by invasive pneumococcal disease (IPD). This is the case when pneumococci can be cultured from normally sterile fluids such as blood, spinal fluid or synovial fluid. Factors that promote the development of a pneumococcal infection are smoking, alcohol abuse and suffering from certain conditions. But there is growing evidence that occupational exposure may also play a role.
Exposure and pneumococcal pneumonia
Thirty years ago, an increased risk of fatal pneumonia was found in welders in a British study (Coggon et al. 1994). Subsequently, this increased risk was also found in occupations with exposure to metal fumes such as foundries, especially in the year after exposure (Palmer et al. 2003, 2009). A prospective cohort study in Sweden showed that construction workers exposed to inorganic dust and metal fumes in the past year have an increased risk of pneumococcal disease (Torén et al. 2011).
Various clusters of pneumococcal pneumonia have been diagnosed in shipyard employees (Wergeland and Iversen 2001; Ewing et al. 2017; Linkevicius et al. 2019). In Sweden, too, invasive pneumococcal disease with pneumonia has been examined in relation to work exposure. There was an increased risk with exposure to inorganic dust and fumes/vapours including metal vapor in the previous year's exposure (Torén et al. 2020a).
The question now is whether cumulative exposure has the same effect on risk in the longer term. This was recently investigated by Torén et al. (2022). The intensity and duration of the exposure were examined and an attempt was made to find an exposure-response relationship. That would add to the evidence for a causal relationship.
To investigate this further, 3184 cases of invasive disease by pneumococci with pneumonia were reviewed. These cases are linked to six controls each from the Swedish population based on the day the patients were diagnosed with the condition.
An employment history was drawn up for all participants and an estimate was made of the prior exposure using a job-exposure matrix (JEM). The size used is intensity years, where the duration of the exposure (maximum 5 years) is multiplied by the estimated intensity of the exposure (0 for not exposed, 1 for low and 4 for high).
Using conditional logistic analyses, the odds ratio (OR) for invasive pneumococcal disease with pneumonia was calculated. This is corrected for co-morbidity (the occurrence of other disorders), level of education, income and other occupational exposure.
The conditions included as co-morbidity are chronic obstructive pulmonary disease (COPD), asthma and ischemic heart disease, diabetes mellitus and alcohol abuse in the five years prior to diagnosis. It was also examined whether people had previously been vaccinated against pneumococci (0,2% of patients and 0,1% of control subjects).
Of the patients with pneumococcal disease, 28% were exposed to inorganic dust compared to 23,4% in the control group. 25% of the patients were exposed to smoke/vapour compared to 23,4% of the control group. The most common co-morbidity was diabetes (9,6% of patients and 4,4% of controls).
When other occupational exposures are taken into account, it appears that more than 5 intensity years of exposure to silica dust or fumes/fumes is associated with an increased risk of invasive pneumococcal disease with pneumonia. The OR for silica dust exposure is 2,53 (95% CI (Confidence Interval 1,49–4,32) and 2,24 (95% CI 1,41–3,55) for fume/vapour exposure.
With less than 5 intensity years of exposure, the ORs are lower; respectively 1,45 (95% CI 1,20–1,76) for silica dust exposure and 1,05 (95% CI 0,94–1,16) for smoke/vapour exposure. No increased risk was found for exposure to organic matter.
In logistic regression, the risk of pneumococcal disease appears to be increased if the patient has worked as a welder or cutter in the past five years (before diagnosis): OR = 3,21 (95% CI 1,63 – 6,32).
Mechanism still unknown
The mechanism underlying the increased risk of pneumococcal pneumonia when exposed to dust and metal fumes in particular is not yet known. It is possible that the inhalation of dust and metal vapor suppresses the alveolar macrophages and thus impairs the pulmonary clearance of pathogens (Ghio 2014; di Benedetto et al. 2016). This means that the airways are less well protected. Another idea is that the ultrafine particles in welding fumes cause the S. pneumoniae stick more easily to the airway epithelium (Suri et al. 2016).
Because exposure to organic dust does not seem to increase the risk, it is thought that especially the metal particles in dust and smoke/vapour, especially iron, increase the risk (Ghio 2014; di Benedetto et al. 2016), possibly because they have a different surface and therefore act differently biologically.
This study shows that the risk of pneumococcal pneumonia increases with increasing cumulative exposure to dust, smoke and vapour.
Torén, K., Blanc, PD, Naidoo, R. et al. Cumulative occupational exposure to inorganic dust and fumes and invasive pneumococcal disease with pneumonia. Int Arch Occup Environment Health 95, 1797–1804 (2022). https://doi.org/10.1007/s00420-022-01848-6
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