Slaughterhouse work is notorious for its harsh conditions and risks to slaughterhouse workers’ health. Among the numerous hazards they face is the high level of bioaerosols, which are underappreciated and largely invisible threats. These organic dust particles, including bacteria and fungi, pass through the air in such environments, posing serious threats to the respiratory health of workers. This study assessed lung function parameters, respiratory symptoms, and associated serum inflammatory markers among slaughterhouse workers.

The study’s results indicated that age and BMI did not differ significantly between the two categories. Nevertheless, an increase in the incidence of respiratory problems and a significant decrease in lung function measurements were identified among laborers in slaughterhouses. The incidence rates of sinusitis, persistent cough, phlegm, wheezes, and breathlessness among workers in slaughterhouses were 22%, 46.3%, 39%, 29.3%, and 43.9%, respectively. Further, these were significantly higher than those of the unexposed workers. These findings agree with those of Kasaeinasab et al. (2017), who worked with 81 slaughterhouse workers in Iran. However, they reported that exposure to bioaerosols was linked to a significant decrease in lung function metrics and an increase in the frequency of respiratory issues among slaughterhouse workers.

Regarding the incidence of respiratory issues and ventilatory function metrics among slaughterhouse employees, to the best of our knowledge, little research has been conducted; therefore, comparing the results is impossible. Nonetheless, the frequency of respiratory conditions among slaughterhouse workers brought on by bioaerosol exposure matched that of workers in poultry farms, composting plants, wastewater treatment, and solid waste management (Viegas et al. 2013; Jahangiri et al. 2015; Taluja et al. 2018).

This research revealed that 31.7% of individuals employed in slaughterhouses experienced moderate airway obstruction, 17.1% had severe airway obstruction, and 4.9% had extremely severe airway obstruction. The mean observed values of FEV1, FEV1/FVC, and FVC were 64.26 ± 19.66, 69.71 ± 13.71, and 75.32 ± 14.62, respectively. Comparatively, obstruction was associated with considerably reduced FVC/FEV1 values among personnel in other animal care facilities, such as poultry houses (Yasmeen et al. 2020).

The current work showed that a higher degree of obstruction was associated with an increase in age and duration of exposure, which is in line with a study conducted by Younis and his colleagues (2020), which suggested that poultry laborers’ years of experience were positively correlated with a decline in lung function capacity.

The results of this study indicated that exposed laborers exhibited a greater inflammatory response than the control group, as measured by increased hsCRP and IL-6 amounts. However, this could be attributed to a high-stress workplace that negatively impacts employee health and elevates oxidative stress, thereby precipitating a rise in inflammation. These results align with those of Zelzer et al. (2018), who examined inflammation and work intensity levels among office and abattoir workers.

Bioaerosol exposure doesn’t just impact the respiratory system directly; it triggers systemic inflammatory responses. Wang and his colleagues (1997) found that exposure to swine dust led to a significant increase in interleukin-6 in the blood. This increase in IL-6 suggests that exposure to bioaerosols triggers an immune response that can affect the entire body, not just the respiratory system.

IL6, which plays a crucial role in triggering and sustaining chronic inflammation, is a keystone cytokine in inflammation. It is synthesized in an area during the early stages of inflammation and subsequently migrates to the liver, where it rapidly induces a wide array of acute-phase proteins, including CRP, fibrinogen, and SAA (Tanaka et al. 2014).

Additionally, elevated levels of hsCRP and IL-6 were found to be correlated with more severe obstructions. This finding aligns with numerous studies reporting higher circulating serum levels of hsCRP and IL-6 among individuals with COPD compared to control subjects. Furthermore, these levels were observed to increase with disease progression. A role in the regulation of the acute inflammatory response, including the control of CRP synthesis and secretion, is played by elevated levels of these markers among individuals with COPD (Bolton et al. 2007; De Moraes et al. 2014; Hussein et al. 2022) .

Moreover, the present study revealed a significant inverse correlation between IL-6 and hsCRP levels and FEV1%, FEV1/FVC, FEF25%, FEF 50%, FEF 75%, and PEF%. However, this agrees with Hussein et al. (2022), who found a significant negative correlation between IL-6 levels and FEV1%, FVC%, and FEF25–75% predicted values.

It is possible to reconcile the correlation between the reduction in FEV1 and FEV1% and the degree of inflammation, fibrosis, and luminal exudates in the small airways. Furthermore, COPD sufferers experience airflow limitation due to increased airflow resistance, which is induced by smooth muscle hypertrophy, goblet cell metaplasia, airway cartilage loss, and mucosal hypersecretion (Haraguchi et al. 1999).

Prolonged exposure to occupational stressors has been found to reduce antioxidative capacity, potentially amplifying the adverse effects of heightened oxidative stressor production resulting from a substantial caseload (Zimet et al. 2016). Li et al. (2012), performed a systematic review of research examining the effects of persistent exposure to air pollution, particulate matter, and smoke on CRP levels in children and adults. The authors discovered that patients exposed for an extended period exhibited elevated CRP levels.

The present investigation revealed a statistically significant positive correlation between the amount of serum hsCRP and IL-6 in the exposed group and age and duration of employment, respectively. This result is comparable to that of Walker et al. (2016), who found inflammation and immune system changes linked to protracted occupational exposure; thus, it emphasizes the need for enhanced workplace risk management.

In addition, a ROC curve was performed for IL-6 and hsCRP as predictors of obstructive ventilatory impairment among slaughterhouse workers. The results indicated that IL-6 and hsCRP had a significantly greater area under the curves, with sensitivity and specificity of 63.4% and 95.1%, and 68.3% and 78%, respectively. The optimal cut-off values for IL-6 and hsCRP were 115.95 (pg/mL) and 4.35 (mg/L), respectively. Huang et al. (2021), hypothesized, based on the ROC curve and AUC, that IL-6 might more accurately reflect the level of systemic inflammation in COPD patients than hs-CRP.

Furthermore, an investigation conducted by Yang et al. (2022), utilized ROC analysis to identify serum hsCRP and IL-6 as autonomous risk factors for chronic obstructive pulmonary disease in conjunction with pulmonary hypertension. Sensitivity, specificity, and critical value for the serum concentration of hsCRP were 90.91%, 85.96%, and 38.49 (mg/L), respectively; sensitivity, specificity, and critical value for IL-6 were 87.27%, 89.47%, and 98.99 (pg/mL), respectively.

Finally, it is, thus, plausible that these cytokines, which are probably produced and released in the airways following exposure to bioaerosols in slaughterhouse environments, are important for the inflammatory reaction and, to some extent, may explain some of the symptoms following exposure.