Mucor, Negative-Pressure Rooms, and the Immunosuppressed

Today the Centers for Disease Control released the long-awaited report on the Mucor mold infections that occurred in the ICU at my home institution. The findings did not contain any major findings that were not well known prior to the report. However, the report is important, nonetheless, as it highlights the ubiquity of mold in the environment and illustrates how immunosuppressed patients are exquisitely--and almost exclusively--at risk.

To recap, there were 3 probable and 1 suspect infection that occurred with mold of the Mucor variety in transplant patients. Of the 4 cases, three were fatal and three occurred in the same ICU room. This type of mold is important given its high mortality rate which is a largely a result of the type of patients it infects (i.e. the immunosuppressed). 

The most important part of the CDC report is the case-control study they conducted. Case control studies are very important at delineating risks and eliminating noise in the quest for a definitive answer to the phenomenon under study.

In this case-control study, the room that 3 of the 4 patients stayed in was found to be the only significant factor that distinguished cases from the controls studied. This result puts to rest any other factor that may have been at play such as contaminated linens, for example.

What was special about this room, according to the CDC report,  was that it was a negative-pressure room which, by design, draws air in (these are the room we use for contagious tuberculosis patients to prevent infectious air from leaking out of the room). Could the negative-pressure have drawn fungal spores in? The room was also located near the exit of the ICU providing a route for spores from visitors's clothes, shoes, and elsewhere outside the to gain some proximity to the negative-pressure room.

It is important to remember that these mold infections, unfortunate and tragic, likely do not represent a major statistical aberration over what would be expected at a major transplant center that cares for some of the sickest patients in the world. FYI, my mother just had surgery at the hospital and I didn't bat an eye over her risk for infection with Mucor.

The report's recommendations to not use negative-pressure rooms for immunosuppressed patients (unless needed), to change some of the geography, and maintain vigilance for future occurrences are valid.