Amoebae and humidifier fever

One hundred and nineteen sera from workers at four different work sites exposed to different contaminated humidifiers were examined by the immunofluorescent antibody (IFA) technique for antibodies to the amoebae Acanthamoeba polyphaga and Naegleria gruberi. Twenty-five of the sera were from workers with humidifier fever (HF) and six from workers with work related asthma (WRA) shown to be due to the contaminated humidifiers. A positive IFA test was found to correlate precipitin reaction to humidifier antigen, but did not correlate with smoking habit, work related symptoms (detected by standard questionnaire) or with HF or WRA. Amoebae were identified in all humidifiers studied.