Objective To study the possible respiratory and haematological effects of endotoxin exposure to bacterial single-cell protein (BSCP) in workers during a follow-up period of 5 years including 4 years of exposure and 1 year without exposure.

Methods The study included 28 workers examined in 2002–2005 and 1 year after exposure termination in 2007. The arithmetic mean endotoxin exposure was 5800–11 000 EU/m³ among the high exposure group and 390 EU/m³ in the low exposure group. Assessment of lung function included spirometry and gas diffusion in 2003, 2004 and 2007. Rhinometry was performed in 2004 and 2007. Blood analysis included leukocyte cell count and measurement of the acute phase proteins: C-reactive protein, interleukin-6, eosinophilic cationic protein, macrophage inflammatory protein-1α, monocyte chemoattractant protein-1, chemoattractant protein RANTES, platelet-derived growth factor BB, fibrinogen and D-dimer.

Results In the low exposure group, but not in the high exposure group, there were significant improvements in both forced vital capacity (FVC) (290 ml) and forced expiratory volume in 1 s (FEV₁) (180–210 ml) (p=0.004–0.03) 1 year after the end of exposure. The number of leukocytes and eosinophilic cationic protein and D-dimer levels increased significantly with increasing endotoxin exposures and decreased significantly 1 year after exposure termination. Changes in acute phase proteins suggested exposure-related tolerance.

Conclusions An inflammatory tendency during an exposure period of 4 years seems to reverse 1 year after cessation of exposure to endotoxins from a single species. Lung function improved significantly among workers exposed to low levels of endotoxin but not among the highly exposed workers.