This extension piece argues against general adoption of incoming-air filtration in commercial poultry houses. Filtering incoming air is characterised as extremely difficult and costly. Clogged filter material further reduces house air exchange rates, which diminishes air quality, which in turn creates bird performance and health problems. The argument is that avian influenza prevention effort belongs first with people, equipment, wild birds and rodents, and it notes correctly that filtered-air positive-pressure houses are typically confined to disease research and vaccine-egg production rather than commercial flocks.
It deserves a place in this library and it deserves to be taken seriously. Note what the objection is not: nobody in this argument disputes that a filter removes pathogen from air. The objection is that a poultry house cannot move the air it needs through loaded media at an acceptable cost, which is a static pressure and airflow problem rather than an efficacy problem. Broiler houses in particular move volumes of air that dwarf a sow farm, and the loading penalty scales with that.
The counterweight is worth holding at the same time. Grunder and colleagues showed in 1975 that filtered positive pressure kept Marek's disease out of a house for 741 days with the disease enzootic on the same farm. Bossers and colleagues detected wild waterbird DNA in the air entering high-biosecurity houses through their inlets, and Elbers and colleagues measured particulate and insects entering inlets and found the load rises in wind-directed openings during storms. The conventional biosecurity this piece prioritises was in place at those farms. Both positions can be true: filtration works, and whether a given building can carry it is a question that has to be answered building by building rather than in general.