PROSPECTIVE-STUDY OF OCCUPATIONAL ASTHMA TO LABORATORY-ANIMAL ALLERGENS - STABILITY OF AIRWAY RESPONSIVENESS TO METHACHOLINE CHALLENGE FOR ONE-YEAR

The stability of airway hyperresponsiveness was studied in a group of 178 young adults working with laboratory animals. At the time of their entry into the study, 132 of 178 subjects (74%) had less than 20% res ponse to the inhalation of 25 mg/ml methacholine, whereas 26 (15%) had a methacholine dose causing a 20% fall in forced expiratory volume in 1 second after fewer than 80 breath units. The distribution of methac hacholine responsiveness did not differ at 6 months and 1 year; 155 of 178 volunteers (90.4%) responded during the repeated challenges to do ses within one dilution of their results at entry. One hundred forty-o ne subjects were consistently unreactive during the year, and 17 were consistently reactive. Approximately equal numbers gained and lost rea ctivity. Those with consistently positive responses to methacholine we re more likely to have skin test reactivity and chest symptoms. The pr esence of consistent chest symptoms was loosely associated with consis tent methacholine responsiveness; 55% of those with consistent hyperre sponsive airways had symptoms and 24% of those who consistently had sy mptoms had hyperresponsive airways. We concluded that the methacholine response is relatively stable during the course of a year in laborato ry animal workers who remain at their jobs and that the presence of a positive skin test response to laboratory animals ol of chest symptoms does not change the pattern of stable responsiveness.