Sera from 43 of 141 (31%) patients with cystic fibrosis living in the United States had precipitating antibodies to antigenic extracts of Aspergillus fumigatus. A similar incidence has been found in London. In general, precipitins are found in more severe cases.
Schwartz RH, Johnstone DE, Holsclaw DS, Dooley RR. Serum Precipitins to Aspergillus fumigatus in Cystic Fibrosis. Am J Dis Child. 1970;120(5):432-433. doi:10.1001/archpedi.1970.02100100096009