Recurrent exposure to Histoplasma capsulatum in modern air-conditioned buildings.
BACKGROUND
Between 1989 and 1996, an epidemic of histoplasmosis occurred on a medical school campus. There had been numerous construction projects on the campus that involved previously wooded land and were adjacent to a large bird sanctuary.


METHODS
We investigated the epidemic with active surveillance to detect cases, a histoplasmin skin-test survey, inspection of the air-filtration systems of the involved buildings, and cultures of soil samples. The investigation also included a simulation of entry into air-intakes of the buildings from spore sources by means of a wind-tunnel analysis of a model of the campus that used inert gas. After control procedures were instituted, sentinel population groups had follow-up with yearly serological tests.


RESULTS
From 1989 through 1996, there were 29 cases of histoplasmosis that occurred among school employees. All cases with a defined onset began during periods of ongoing campus construction. Positivity rates for histoplasmin skin testing were higher among on-campus personnel (47%) than among off-campus employee control subjects (28%) (P<.001); the rates were highest in employees who worked on the upper floors of 2 research buildings. The air-handling units on the roofs of these buildings were not designed to exclude Histoplasma spores. The wind-tunnel experiment indicated that spores aerosolized in the bird sanctuary were not taken into campus buildings.


CONCLUSIONS
The major sources of employee exposure to H. capsulatum spores were the construction sites. Low-level, recurrent exposures occurred over several years inside modern research buildings. This phenomenon, which has not been previously described, may play a role in the epidemiology of spore-transmitted diseases in urban settings.
University of Texas Southwestern Medical Center, Dallas, TX 75390-9113, USA. James.Luby@UTSouthwestern.edu
James P
JP
Luby
Paul M
PM
Southern
Charles E
CE
Haley
Kirby L
KL
Vahle
Robert S
RS
Munford
Robert W
RW
Haley
D000389:Air Conditioning; D004196:Disease Outbreaks; D004197:Disease Reservoirs / Q000382:microbiology; D005160:Facility Design and Construction; D006660:Histoplasmosis / Q000453:epidemiology* / Q000382:microbiology / Q000635:transmission*; D006801:Humans; D016015:Logistic Models; D009790:Occupations; D012307:Risk Factors; D012882:Skin Tests; D020308:Songbirds / Q000382:microbiology