Background Laboratory animal workers face the risk of developing an IgE-associated respiratory allergy to airborne proteins, such as Mus m 1 (mouse urinary protein). Approximately 15% of exposed employees will develop IgE sensitisation and 10% clinically apparent disease. We have recently embarked on a large study called SPIRAL (Safe Practice In Reduction of Allergy in Laboratories) to gain a greater understanding of laboratory animal allergy (LAA) and to determine whether we can devise a code of safe practice to prevent, as far as possible, the future occurrence of LAA.

Aim To determine personal exposure to Mus m 1 within animal facilities where mice are housed exclusively in open cages and exclusively in individually ventilated cages (IVC).

Methods Selected employees wore Casella Apex pumps (2 L/min) during their full shifts to collect inhalable particulate onto fluoropore membrane (1 µm), 25 mm filters using IOM sampling heads.82 filters from an IVC facility and 56 filters from an open cage facility were analysed for Mus m 1 using a commercial sandwich enzyme linked immunoassay (Indoor Biotechnology).

Results The range of Mus m 1 levels within the IVC facility was 0.00–66.33 ng/m³ and in the open cage facility was 3.89–305.59 ng/m³. 11 (13%) of samples from the IVC facility and 50 (89%) of samples from the open cage facility had a Mus m 1 exposure level greater than 5 ng/m³. Additionally, there was substantial variation when task specific sampling was carried out over short periods of time compared with full shift sampling. Further analyses will allow us to identify which tasks were associated with highest levels of exposures.

Conclusions The majority of samples from the open cage facility were above 5 ng/m³, a figure previously suggested to limit or reduce incidence of LAA. Although use of IVCs has been shown to reduce exposure to Mus m 1, we found several samples above 5 ng/m³. Exposure to high allergen levels will be influenced by cage type, variation in individual working practices and carrying out of specific “high-risk” tasks; some of these factors may be modifiable and these results may be used to change practice.