A protocol to aid in the diagnosis of occupational asthma to Alaska pollock and Yellowfin sole

Leonard C. Altman, MD⁎, †, Andrew G. Ayars, Division of Allergy and Infectious Diseases, University of Washington, Seattle, Washington † Northwest Asthma and Allergy Center, Seattle, Washington Available online 14 March 2012.


Occupational asthma has been described in workers exposed to aerosolized Alaska pollock and Yellowfin sole. We present a protocol to aid in the diagnosis of this unique occupational asthma as well as the results of 11 inhalation challenges.

Harvesting and processing Alaska pollock (Theragra chalcogramma) and Yellowfin sole (Limanda aspera) have become economically significant aspects of the fishing industry in Alaska. The Alaska pollock fishery is the largest in the United States by volume according to the National Oceanic and Atmospheric Administration (NOAA).1 Yellowfin sole is one of the most abundant flatfish species in the eastern Bering Sea and is the largest flatfish fishery in the United States.2 Workers live on factory ships, where they sort, process, and freeze the harvested fish. Some workers on these ships have reported asthma-like symptoms that appear to be related to exposure to aerosolized fish byproduct. A recent cross-sectional study conducted on 594 workers in fish processing plants found that although 16% of workers had asthma-like symptoms, only 6% were sensitized to fish species on skin testing, suggesting that not all symptoms can be attributable to and allergy to fish.3

The diagnosis of suspected occupational asthma attributable to seafood allergy typically involves skin prick testing and pulmonary function testing; however, no published method exists for specific inhalation challenge (SIC) to test for occupational asthma to Alaska pollock or Yellowfin sole. The most recent American College of Chest Physicians consensus guidelines recommends the use of SIC to evaluate the diagnosis of sensitizer-induced occupational asthma.4 We present a method to aid in the diagnosis of suspected occupational asthma to these 2 fish and the results of evaluations in 11 patients.

We prepared an extract of macerated fish flesh in aqueous solution to perform skin testing and bronchoprovocation challenges. Antigen was prepared by soaking macerated Alaska pollock or Yellowfin sole for 2 weeks in a ratio of 10 g fish to 100 mL sterile 0.9% saline and storing at 2 to 8°C. The solution was then decanted and centrifuged at 500 g for 10 minutes. The supernatant was aspirated and filtered through a 0.2-μm filter unit (Pall Life Services; Ann Arbor, Michigan), and this was defined as the 1:10 strength. Tenfold dilutions were then prepared with sterile saline to form 1:100 and 1:1,000 concentrations. A Bradford protein assay was performed, which showed 80 μg/mL in the 1:10 pollock extract and 28 μg/mL in the 1:10 Yellowfin sole extract.5 Skin prick testing was performed at the 1:10 strength followed by intradermal testing at the 1:1,000 strength if necessary, along with positive and negative controls. Inhalation challenge was conducted by a single-blind, saline-controlled exposure with compressed air at 18 psi, using a Hudson nebulizer and heat and moisturizing filter. Delivery of aqueous fish extract was performed starting at the 1:1,000 strength for 5 to 15 minutes, with 3 minutes rest followed by pulmonary function testing measurements. Patients were subsequently exposed to the 1:100 and 1:10 dilutions as necessary. Positive challenges were defined as a 20% drop in forced expiratory volume in 1 second from saline baseline, and the patients were observed for an additional 2 to 3 hours.

We performed inhalation challenges in 11 patients with suspected occupational disease from fish products; 9 were tested with an extract of Alaska pollock and 2 with Yellowfin sole (Table 1). The most common historical symptoms were shortness of breath, cough, and wheezing. Five of the 9 patients challenged with Alaska pollock and 2 of 2 challenged to Yellowfin sole had positive responses. Six of the 7 patients with a positive inhalation challenge reacted at the 1:10 concentration and one at the 1:100 concentration. No patients reacted at the 1:1,000 strength, and all patients tolerated the procedure without significant adverse events.

Skin testing was positive (defined as 3/5 mm or greater, wheal/erythema) in all but 1 patient, and this subject had a negative bronchoprovocation challenge. All 7 patients with a positive inhalation challenge had a positive skin prick test. The positive predictive value of skin prick testing was only 70%; therefore, skin test and history alone are not sufficient to predict a positive inhalation challenge.

According to the most recent guidelines,4 assessment of nonspecific bronchial hyperresponsiveness and serial peak expiratory flow should be performed to evaluate occupational asthma. However, the patients we evaluated were not permitted by their employers to return to work until the SIC was completed, so serial pre and post work peak expiratory flow measurements were not possible.

In this report we present a protocol to aid in the diagnosis of occupational asthma caused by aerosolized Alaska pollock and Yellowfin sole. The patients with positive inhalation challenges were advised not to return to work, avoid the factory where fish is processed, or use respirator face masks.


We thank Christina Chan (Wight Lab, Benaroya Research Institute, Seattle WA) for performing the protein assay on extract samples.

Table 1. Summary of subjects tested with inhalation challenge (n = 11)

Patient   Fish               Symptoms                                    Age  Sex Skin test        Inhalation challenge (Dilution)

1         Pollock            Cough, fever                                46   M   Positive (SPT)   Negative

2         Pollock            Shortness of breath, wheezing               44   M   Positive (SPT)   Positive (1:10)

3         Pollock            Cough, dizziness, wheezing                  37   F   Positive (ID)    Negative

4         Pollock            Shortness of breath, wheezing               60   F   Positive (ID)    Negative

5         Pollock            Chest congestion, shortness of breath       39   M   Positive (SPT)   Positive (1:10)

6         Pollock            Fever, shortness of breath, wheezing        50   M   Positive (ID)    Positive (1:10)

7         Pollock            Shortness of breath, wheezing               35   M   Positive (ID)    Positive (1:10)

8         Pollock            Chest congestion, shortness of breath       34   M   Positive (SPT)   Positive (1:100)

9         Pollock            Cough, shortness of breath                  50   M   Negative         Negative

10        Yellowfin Sole     Cough, shortness of breath                  28   M   Positive (SPT)   Positive (1:10)

11        Yellowfin Sole     Shortness of breath, wheezing               47   M   Positive (SPT)   Positive (1:10)

Abbreviations: SPT, skin prick testing (1:10 dilution); ID, Intradermal (1:1,000 dilution); M, male; F, female.