Asthma diagnosed after 11 September 2001 among rescue and recovery workers: findings from the World Trade Center Health Registry.

The authors observed a significant protective association between the use of respirators with cartridges and changes in pulmonary function after 11 September 2001, but the association did not reach statistical significance for respiratory symptoms and was not significant in either case for dust masks alone.

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The net direction of the resulting bias is unknowable, although it is unlikely to act in such a way as to produce an apparent trend between newly diagnosed asthma and increasing delay in mask or respirator use.

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