Molecular typing of environmental and patient isolates of Aspergillus fumigatus from various hospital settings

Abstract

Fingerprinting of more than 700 clinical and environmental isolates of Aspergillus fumigatus from four differential hospital settings was undertaken with a dispersed repeated DNA sequence. The analysis of the environmental isolates showed that the airborne A. fumigatus population is extremely diverse, with 85% of the strains being represented as a single genotype isolated once. The remaining 15% of the strains were isolated several times and were able to persist for several months in the same hospital environment. No strains were found to be associated with a specific location inside the hospital, and identical strains were isolated from different buildings of the hospital and outdoors. Isolation of the same strain both from patients and from the environment of the same hospital is highly suggestive of a nosocomial infection. The characteristics of the environmental fungal population explains the two main results obtained from the typing of the clinical isolates: (i) the absence of a common strain responsible for an invasive aspergillosis outbreak results from the extreme diversity of the environmental population of A. fumigatus in contact with the patients, and (ii) patients hospitalized in different wards of the same hospital can be infected with the same strain since every patient might inhale the same spore population.

FIG. 1

Temporal evolution of the concentration of spores in the air (•) and on the surfaces (○) of hospitals I and II. The numbers of conidia per cubic meter (co/m³) of air or per square meter (co/m²) of surface were estimated.

FIG. 2

Number of isolates per genotype isolated at least twice in hospital I (closed bars) and maximal time interval (in months) separating the isolation of two isolates of the same genotype (open bars).

FIG. 3

Map of hospital I showing the number of isolates typed and the different strains encountered in the different locations sampled. For each location, the ratio x/y indicates the number of unique genotypes (x)/the total number of genotypes (y) collected at the spot. A, M, and G, three sectors of the Hematology Unit situated at the third floor of building A; OPC, outpatient clinic at the basement of building B.

FIG. 4

Number of isolates per genotype isolated at least twice in hospital II (closed bars) and maximal time interval between the isolation of two identical isolates within the same genotype (open bars).

FIG. 5

Location of the identical isolates from the 19 genotypes found at least twice in hospital II. The numbers 1 to 4 indicate the first, second, third, and fourth floors of the building surveyed, respectively; 0 indicates outside the building.

FIG. 6

Temporal distribution of environmental and clinical isolates in the bone marrow transplant unit of hospital III showing the identities (isolates indicated by the shaded boxes) between isolates collected from patients (P numbers) and from the environment. The patients infected with isolates identical to the environmental isolates are indicated in italics at the left of the environment column. Isolates from the same patients belonging to different genotypes are indicated by a broken line. Only one genotype has been repeatedly isolated from three patients (marked with asterisks).

FIG. 7

Dendrogram (unweighted pair group with arithmetic averages) of the clinical isolates analyzed in hospital IV. The date of isolation and the different buildings (marked with different letters) where the patient (P) was hospitalized are indicated. Identities between isolates are framed. The scale at the top represents percent identity.