Histoplasmosis is the most common pulmonary mycosis in the United States. T
he responsible fungal pathogen, Histoplasma capsulatum, grows in soils cont
aminated with bird or bat droppings. Inhalation of dust from contaminated a
reas containing H. capsulatum spores is a primary route of infection. The a
bility to detect H. capsulatum in soil samples has been limited by the lack
of fast, reliable and inexpensive methods. A polymerase chain reaction (PC
R) method was developed that allows the direct detection of H. capsulatum i
n soil. A two-stage PCR protocol was followed employing both fungal-specifi
c primers and nested primers specific for the internal transcribed spacer (
ITS) region of the 5.8S rRNA gene of H. capsulatum. The estimated limit of
detection of this method is 10 spores. In contrast to the more expensive an
d indirect mouse inoculum assay, wh ich requires 6-8 weeks for sample analy
sis, PCR analysis of soil contaminated with H, capsulatum can be completed
in less than 2 days.