Extrinsic allergic alveolitis

Extrinsic allergic alveolitis (EAA) refers to a group of lung diseases that can develop after exposure to certain substances. The name describes the origin and the nature of these diseases:

  • 'extrinsic' - caused by something originating outside the body
  • 'allergic' - an abnormally increased (hypersensitive) body reaction to a common substance
  • 'alveolitis' - inflammation in the small air sacs of the lungs (alveoli)

Symptoms can include: fever, cough, worsening breathlessness and weight loss. The diagnosis of the disease is based on a history of symptoms after exposure to the allergen and a range of clinical tests which usually includes: X-rays or CT scans, lung function and blood tests.

EAA is not a 'new' occupational respiratory disease and occupational causes include bacteria, fungi, animal proteins, plants and chemicals.

Examples of EAA include:

Farmer's lung

This is probably the most common occupational form of EAA and is the outcome of an allergic response to a group of microbes, which form mould on vegetable matter in storage. During the handling of mouldy straw, hay or grain, particularly in a confined space such as a poorly ventilated building, inhalation of spores and other antigenic material is very likely.

There also appears to be a clear relationship between water content of crops, heating (through mould production) and microbial growth, and this would apply to various crops and vegetable matter, with the spores produced likely to cause EAA.

Farmer's lung can be prevented by drying crops adequately before storage and by ensuring good ventilation during storage. Respiratory protection should also be worn by farm workers when handling stored crops, particularly if they have been stored damp or are likely to be mouldy.

Metal working fluid and EAA

Exposure to contaminated metal working fluid (MWF) has been responsible for workplace outbreaks of EAA in the US over the last 15 years, and more recently also in the UK.

MWF, also referred to as suds, coolant, slurry or soap, is a generic term covering a wide variety of fluids used as lubricants or coolants for metal machining processes such as drilling, milling and turning.

Exposure to MWF can occur by direct contact with the skin (which can give rise to contact dermatitis or by inhalation of MWF mist generated during machining. The greatest risk of respiratory symptoms is in people working with water-mix MWF.

Note: In addition to EAA, contaminated MWF exposure has been more strongly associated with the development of occupational asthma, as well as other rarer occupational lung diseases such as lipoid pneumonia and bronchopulmonary aspergillosis.

Further information

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Updated: 2021-01-18