Patient information: Female, 51 years old
Chief complaint: Eye congestion, foreign body sensation
Past history: No remarkable past medical history
Smoking history and alcohol history: None
Occupational history: Meat cutting (duck parts). Worked since July 1, 2009.
Present illness: Stinging eyes and foreign body sensation had occurred from mid-December, 2012; eye congestion had also occurred frequently. Symptoms became worse in the presence of bright light. Ocular symptoms mostly occurred later in the working day and after work. Skin exfoliation and redness was observed around the eyes and on the face.
Physical examination: Mild hyperemic conjunctiva (+), erythematous diffuse patches (+), facial reddish papule (+), pruritic and stinging sense (+).
Laboratory findings: A peripheral blood examination revealed the following: hemoglobin level 11.9 g/dL, hematocrit 35.9 %, white blood cell count 4,500/mm3, and platelet count 180,000/mm3. According to an immunoassay, IgA was 214.0 mg/dL, IgE was 58.80 IU/ml. All these lab findings were within the normal range.
Pulmonary function test findings: A pulmonary function test revealed the following: functional vital capacity (FVC) was 3.68 L (115.4 %), forced expiratory volume in one second (FEV1) was 3.00 L (124.5 %), the ratio of FEV1 to FVC was 81.52 % (108.8 %). All findings were within the normal range.
Medical imaging findings: There were no significant findings upon plain chest radiography.
Ophthalmology findings: Visual acuity was 0.1 in the right eye and 0.08 in the left. Maintained anterior chamber or anterior chamber cells were not observed in either eye. Intra ocular pressure was 14 mmHg in the right eye and 14 mmHg in the left. Schirmer`s test result was 20 mm in the right eye and 18 mm in the left. Diffuse corneal damage was observed (Figs. 2 and 3). On the basis of these results, keratoepitheliopathy was diagnosed.
At the time of medical examination by interview, 26 out of a total of 41 workers (64 %) were complaining of ocular symptoms (stinging eye, teardrops, etc.). Moreover, skin symptoms (skin exfoliation, redness) were found in 4 workers (9 %) upon physical examination. Ocular symptoms mostly occurred immediately after finishing work or after going home, and skin symptoms around the eyes often occurred in workers. None of the workers had an abnormal complete blood cell count, and all Ig A and Ig E tests were normal. In addition, plain chest radiography and pulmonary function tests showed no abnormal findings in any of the workers. An ophthalmic examination yielded normal conjunctival findings in all workers; however, 26 out of 41 workers (63.4 %) were diagnosed with keratoepitheliopathy (Table 2). That is, all of the workers who had complained of the symptoms were diagnosed with keratoepitheliopathy.
The abattoir processed chickens and ducks, and process flow involved 4 steps in the following order: mooring, cutting of meat, evisceration and cleaning, and selection.
There were no significant differences among the processes with regard to the frequencies of workers who complained of ocular symptoms (p = 0.142) or skin symptoms (p = 0.112) (Table 3). These results confirmed that the symptoms were not caused by any specific process.
There were no significant differences among the processes in terms of keratoepitheliopathy patient frequency (p = 0.393) (Table 4).
Exposure to chemical substances and UV radiation was measured. Workplace environmental monitoring was conducted, focusing on 3 processes: cleaning, cleaning finish, and evisceration and hooking, wherein chlorine, hydrochloric acid, and sodium hydroxide was measured. The workers were not exposed to all 3 chemical substances in all processes, and even in processes where they were exposed, the exposure was well below the permitted limit (Table 5).
Workers had none of respiratory symptoms or mucous membrane irritation symptoms that can manifest after exposure to the above chemical substances. In addition, there were no abnormal findings in the pulmonary function test, so that it was not possible to explain the skin and ocular symptoms in terms of exposure to the above chemical substances. What is more, while chemical substances were only used in the department of cleaning and evisceration, keratoepitheliopathy appeared in all departments. Therefore, it was clear on the basis of these findings that exposure to chemical substances was not the cause of the outbreak.
Photokeratitis caused by UV radiation was also suspected - based on the ocular and skin symptoms of the workers. For this reason, the effective radiation dose from the UV disinfection lamp was measured. The apron disinfection lamp at the 1st floor was measured and it was found that it emitted UV-B at 15-30 muW/cm2 and UV-C at 40-160 muW/cm2 with a 5-10 cm measuring distance. The lamp at the 2nd floor emitted UV-B at 7-10 muW/cm2 and UV-C at 40-200 muW/cm2. On both floors, these measurements exceeded the exposure limit (American Conference of Governmental Industrial Hygienists [ACGIH] threshold limit values: 10 min at 5 muW/cm2, 5 min at 10 muW/cm2; Table 6).
The apron disinfection lamps and UV lamps, in the factory are set to turn off automatically when the door of the disinfection equipment is opened. However, this setting was found to be malfunctioning, and the UV lamps of the disinfection equipment were remaining on when the door was opened. Since workers in all processes need to wear and remove aprons several times a day, it was determined that each individual may have been exposed to the UV radiation of the apron disinfection lamps from a short distance for at least 10 min a day (Fig. 4). It was therefore possible that all workers had been exposed to UV radiation for a significant amount of time, thus potentially explaining the ocular symptoms and keratoepitheliopathy that had occurred in a broad range of workers regardless of process. Furthermore, this was the likely explanation for the sunburn-like skin lesions on the face by exposure to UV. Further evidence was provided when workers' ocular and skin symptoms improved after removal of the UV disinfection lamps. Taken together, it was highly potential that the mass photokeratitis that had occurred in the poultry abattoir was caused by exposure to UV radiation from the apron disinfection lamps.